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bd28b14591
I'm looking at trying to possibly merge the 32-bit and 64-bit versions of the x86 uaccess.h implementation, but first this needs to be cleaned up. For example, the 32-bit version of "__copy_from_user_inatomic()" is mostly the special cases for the constant size, and it's actually almost never relevant. Most users aren't actually using a constant size anyway, and the few cases that do small constant copies are better off just using __get_user() instead. So get rid of the unnecessary complexity. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
3289 lines
88 KiB
C
3289 lines
88 KiB
C
/*
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* Fast Userspace Mutexes (which I call "Futexes!").
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* (C) Rusty Russell, IBM 2002
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*
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* Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
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* (C) Copyright 2003 Red Hat Inc, All Rights Reserved
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*
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* Removed page pinning, fix privately mapped COW pages and other cleanups
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* (C) Copyright 2003, 2004 Jamie Lokier
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*
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* Robust futex support started by Ingo Molnar
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* (C) Copyright 2006 Red Hat Inc, All Rights Reserved
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* Thanks to Thomas Gleixner for suggestions, analysis and fixes.
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*
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* PI-futex support started by Ingo Molnar and Thomas Gleixner
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* Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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* Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
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*
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* PRIVATE futexes by Eric Dumazet
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* Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
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*
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* Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
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* Copyright (C) IBM Corporation, 2009
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* Thanks to Thomas Gleixner for conceptual design and careful reviews.
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*
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* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
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* enough at me, Linus for the original (flawed) idea, Matthew
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* Kirkwood for proof-of-concept implementation.
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*
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* "The futexes are also cursed."
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* "But they come in a choice of three flavours!"
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/slab.h>
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#include <linux/poll.h>
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#include <linux/fs.h>
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#include <linux/file.h>
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#include <linux/jhash.h>
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#include <linux/init.h>
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#include <linux/futex.h>
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#include <linux/mount.h>
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#include <linux/pagemap.h>
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#include <linux/syscalls.h>
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#include <linux/signal.h>
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#include <linux/export.h>
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#include <linux/magic.h>
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#include <linux/pid.h>
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#include <linux/nsproxy.h>
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#include <linux/ptrace.h>
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#include <linux/sched/rt.h>
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#include <linux/hugetlb.h>
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#include <linux/freezer.h>
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#include <linux/bootmem.h>
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#include <linux/fault-inject.h>
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#include <asm/futex.h>
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#include "locking/rtmutex_common.h"
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/*
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* READ this before attempting to hack on futexes!
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*
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* Basic futex operation and ordering guarantees
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* =============================================
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*
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* The waiter reads the futex value in user space and calls
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* futex_wait(). This function computes the hash bucket and acquires
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* the hash bucket lock. After that it reads the futex user space value
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* again and verifies that the data has not changed. If it has not changed
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* it enqueues itself into the hash bucket, releases the hash bucket lock
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* and schedules.
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*
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* The waker side modifies the user space value of the futex and calls
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* futex_wake(). This function computes the hash bucket and acquires the
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* hash bucket lock. Then it looks for waiters on that futex in the hash
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* bucket and wakes them.
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*
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* In futex wake up scenarios where no tasks are blocked on a futex, taking
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* the hb spinlock can be avoided and simply return. In order for this
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* optimization to work, ordering guarantees must exist so that the waiter
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* being added to the list is acknowledged when the list is concurrently being
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* checked by the waker, avoiding scenarios like the following:
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*
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* CPU 0 CPU 1
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* val = *futex;
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* sys_futex(WAIT, futex, val);
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* futex_wait(futex, val);
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* uval = *futex;
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* *futex = newval;
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* sys_futex(WAKE, futex);
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* futex_wake(futex);
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* if (queue_empty())
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* return;
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* if (uval == val)
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* lock(hash_bucket(futex));
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* queue();
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* unlock(hash_bucket(futex));
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* schedule();
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*
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* This would cause the waiter on CPU 0 to wait forever because it
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* missed the transition of the user space value from val to newval
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* and the waker did not find the waiter in the hash bucket queue.
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*
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* The correct serialization ensures that a waiter either observes
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* the changed user space value before blocking or is woken by a
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* concurrent waker:
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*
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* CPU 0 CPU 1
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* val = *futex;
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* sys_futex(WAIT, futex, val);
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* futex_wait(futex, val);
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*
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* waiters++; (a)
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* smp_mb(); (A) <-- paired with -.
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* |
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* lock(hash_bucket(futex)); |
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* |
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* uval = *futex; |
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* | *futex = newval;
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* | sys_futex(WAKE, futex);
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* | futex_wake(futex);
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* |
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* `--------> smp_mb(); (B)
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* if (uval == val)
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* queue();
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* unlock(hash_bucket(futex));
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* schedule(); if (waiters)
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* lock(hash_bucket(futex));
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* else wake_waiters(futex);
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* waiters--; (b) unlock(hash_bucket(futex));
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*
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* Where (A) orders the waiters increment and the futex value read through
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* atomic operations (see hb_waiters_inc) and where (B) orders the write
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* to futex and the waiters read -- this is done by the barriers for both
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* shared and private futexes in get_futex_key_refs().
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*
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* This yields the following case (where X:=waiters, Y:=futex):
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*
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* X = Y = 0
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*
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* w[X]=1 w[Y]=1
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* MB MB
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* r[Y]=y r[X]=x
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*
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* Which guarantees that x==0 && y==0 is impossible; which translates back into
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* the guarantee that we cannot both miss the futex variable change and the
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* enqueue.
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*
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* Note that a new waiter is accounted for in (a) even when it is possible that
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* the wait call can return error, in which case we backtrack from it in (b).
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* Refer to the comment in queue_lock().
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*
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* Similarly, in order to account for waiters being requeued on another
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* address we always increment the waiters for the destination bucket before
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* acquiring the lock. It then decrements them again after releasing it -
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* the code that actually moves the futex(es) between hash buckets (requeue_futex)
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* will do the additional required waiter count housekeeping. This is done for
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* double_lock_hb() and double_unlock_hb(), respectively.
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*/
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#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
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int __read_mostly futex_cmpxchg_enabled;
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#endif
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/*
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* Futex flags used to encode options to functions and preserve them across
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* restarts.
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*/
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#define FLAGS_SHARED 0x01
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#define FLAGS_CLOCKRT 0x02
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#define FLAGS_HAS_TIMEOUT 0x04
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/*
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* Priority Inheritance state:
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*/
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struct futex_pi_state {
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/*
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* list of 'owned' pi_state instances - these have to be
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* cleaned up in do_exit() if the task exits prematurely:
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*/
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struct list_head list;
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/*
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* The PI object:
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*/
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struct rt_mutex pi_mutex;
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struct task_struct *owner;
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atomic_t refcount;
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union futex_key key;
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};
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/**
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* struct futex_q - The hashed futex queue entry, one per waiting task
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* @list: priority-sorted list of tasks waiting on this futex
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* @task: the task waiting on the futex
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* @lock_ptr: the hash bucket lock
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* @key: the key the futex is hashed on
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* @pi_state: optional priority inheritance state
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* @rt_waiter: rt_waiter storage for use with requeue_pi
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* @requeue_pi_key: the requeue_pi target futex key
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* @bitset: bitset for the optional bitmasked wakeup
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*
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* We use this hashed waitqueue, instead of a normal wait_queue_t, so
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* we can wake only the relevant ones (hashed queues may be shared).
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*
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* A futex_q has a woken state, just like tasks have TASK_RUNNING.
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* It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
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* The order of wakeup is always to make the first condition true, then
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* the second.
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*
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* PI futexes are typically woken before they are removed from the hash list via
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* the rt_mutex code. See unqueue_me_pi().
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*/
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struct futex_q {
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struct plist_node list;
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struct task_struct *task;
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spinlock_t *lock_ptr;
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union futex_key key;
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struct futex_pi_state *pi_state;
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struct rt_mutex_waiter *rt_waiter;
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union futex_key *requeue_pi_key;
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u32 bitset;
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};
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static const struct futex_q futex_q_init = {
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/* list gets initialized in queue_me()*/
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.key = FUTEX_KEY_INIT,
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.bitset = FUTEX_BITSET_MATCH_ANY
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};
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/*
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* Hash buckets are shared by all the futex_keys that hash to the same
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* location. Each key may have multiple futex_q structures, one for each task
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* waiting on a futex.
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*/
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struct futex_hash_bucket {
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atomic_t waiters;
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spinlock_t lock;
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struct plist_head chain;
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} ____cacheline_aligned_in_smp;
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/*
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* The base of the bucket array and its size are always used together
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* (after initialization only in hash_futex()), so ensure that they
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* reside in the same cacheline.
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*/
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static struct {
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struct futex_hash_bucket *queues;
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unsigned long hashsize;
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} __futex_data __read_mostly __aligned(2*sizeof(long));
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#define futex_queues (__futex_data.queues)
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#define futex_hashsize (__futex_data.hashsize)
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/*
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* Fault injections for futexes.
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*/
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#ifdef CONFIG_FAIL_FUTEX
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static struct {
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struct fault_attr attr;
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bool ignore_private;
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} fail_futex = {
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.attr = FAULT_ATTR_INITIALIZER,
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.ignore_private = false,
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};
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static int __init setup_fail_futex(char *str)
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{
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return setup_fault_attr(&fail_futex.attr, str);
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}
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__setup("fail_futex=", setup_fail_futex);
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static bool should_fail_futex(bool fshared)
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{
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if (fail_futex.ignore_private && !fshared)
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return false;
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return should_fail(&fail_futex.attr, 1);
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}
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#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
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static int __init fail_futex_debugfs(void)
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{
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umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
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struct dentry *dir;
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dir = fault_create_debugfs_attr("fail_futex", NULL,
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&fail_futex.attr);
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if (IS_ERR(dir))
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return PTR_ERR(dir);
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if (!debugfs_create_bool("ignore-private", mode, dir,
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&fail_futex.ignore_private)) {
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debugfs_remove_recursive(dir);
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return -ENOMEM;
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}
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return 0;
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}
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late_initcall(fail_futex_debugfs);
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#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
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#else
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static inline bool should_fail_futex(bool fshared)
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{
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return false;
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}
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#endif /* CONFIG_FAIL_FUTEX */
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static inline void futex_get_mm(union futex_key *key)
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{
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atomic_inc(&key->private.mm->mm_count);
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/*
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* Ensure futex_get_mm() implies a full barrier such that
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* get_futex_key() implies a full barrier. This is relied upon
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* as smp_mb(); (B), see the ordering comment above.
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*/
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smp_mb__after_atomic();
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}
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/*
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* Reflects a new waiter being added to the waitqueue.
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*/
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static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
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{
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#ifdef CONFIG_SMP
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atomic_inc(&hb->waiters);
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/*
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* Full barrier (A), see the ordering comment above.
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*/
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smp_mb__after_atomic();
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#endif
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}
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/*
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* Reflects a waiter being removed from the waitqueue by wakeup
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* paths.
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*/
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static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
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{
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#ifdef CONFIG_SMP
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atomic_dec(&hb->waiters);
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#endif
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}
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static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
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{
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#ifdef CONFIG_SMP
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return atomic_read(&hb->waiters);
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#else
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return 1;
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#endif
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}
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/*
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* We hash on the keys returned from get_futex_key (see below).
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*/
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static struct futex_hash_bucket *hash_futex(union futex_key *key)
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{
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u32 hash = jhash2((u32*)&key->both.word,
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(sizeof(key->both.word)+sizeof(key->both.ptr))/4,
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key->both.offset);
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return &futex_queues[hash & (futex_hashsize - 1)];
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}
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/*
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* Return 1 if two futex_keys are equal, 0 otherwise.
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*/
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static inline int match_futex(union futex_key *key1, union futex_key *key2)
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{
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return (key1 && key2
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&& key1->both.word == key2->both.word
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&& key1->both.ptr == key2->both.ptr
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&& key1->both.offset == key2->both.offset);
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}
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/*
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* Take a reference to the resource addressed by a key.
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* Can be called while holding spinlocks.
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*
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*/
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static void get_futex_key_refs(union futex_key *key)
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{
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if (!key->both.ptr)
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return;
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switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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case FUT_OFF_INODE:
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ihold(key->shared.inode); /* implies smp_mb(); (B) */
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break;
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case FUT_OFF_MMSHARED:
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futex_get_mm(key); /* implies smp_mb(); (B) */
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break;
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default:
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/*
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* Private futexes do not hold reference on an inode or
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* mm, therefore the only purpose of calling get_futex_key_refs
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* is because we need the barrier for the lockless waiter check.
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*/
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smp_mb(); /* explicit smp_mb(); (B) */
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}
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}
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/*
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* Drop a reference to the resource addressed by a key.
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* The hash bucket spinlock must not be held. This is
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* a no-op for private futexes, see comment in the get
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* counterpart.
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*/
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static void drop_futex_key_refs(union futex_key *key)
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{
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if (!key->both.ptr) {
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/* If we're here then we tried to put a key we failed to get */
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WARN_ON_ONCE(1);
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return;
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}
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switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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case FUT_OFF_INODE:
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iput(key->shared.inode);
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break;
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case FUT_OFF_MMSHARED:
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mmdrop(key->private.mm);
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break;
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}
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}
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/**
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* get_futex_key() - Get parameters which are the keys for a futex
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* @uaddr: virtual address of the futex
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* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
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* @key: address where result is stored.
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* @rw: mapping needs to be read/write (values: VERIFY_READ,
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* VERIFY_WRITE)
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*
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* Return: a negative error code or 0
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*
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* The key words are stored in *key on success.
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*
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* For shared mappings, it's (page->index, file_inode(vma->vm_file),
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* offset_within_page). For private mappings, it's (uaddr, current->mm).
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* We can usually work out the index without swapping in the page.
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*
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* lock_page() might sleep, the caller should not hold a spinlock.
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*/
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static int
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get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
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{
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unsigned long address = (unsigned long)uaddr;
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struct mm_struct *mm = current->mm;
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struct page *page;
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struct address_space *mapping;
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int err, ro = 0;
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/*
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* The futex address must be "naturally" aligned.
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*/
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key->both.offset = address % PAGE_SIZE;
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if (unlikely((address % sizeof(u32)) != 0))
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return -EINVAL;
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address -= key->both.offset;
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if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
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return -EFAULT;
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if (unlikely(should_fail_futex(fshared)))
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return -EFAULT;
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/*
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* PROCESS_PRIVATE futexes are fast.
|
|
* As the mm cannot disappear under us and the 'key' only needs
|
|
* virtual address, we dont even have to find the underlying vma.
|
|
* Note : We do have to check 'uaddr' is a valid user address,
|
|
* but access_ok() should be faster than find_vma()
|
|
*/
|
|
if (!fshared) {
|
|
key->private.mm = mm;
|
|
key->private.address = address;
|
|
get_futex_key_refs(key); /* implies smp_mb(); (B) */
|
|
return 0;
|
|
}
|
|
|
|
again:
|
|
/* Ignore any VERIFY_READ mapping (futex common case) */
|
|
if (unlikely(should_fail_futex(fshared)))
|
|
return -EFAULT;
|
|
|
|
err = get_user_pages_fast(address, 1, 1, &page);
|
|
/*
|
|
* If write access is not required (eg. FUTEX_WAIT), try
|
|
* and get read-only access.
|
|
*/
|
|
if (err == -EFAULT && rw == VERIFY_READ) {
|
|
err = get_user_pages_fast(address, 1, 0, &page);
|
|
ro = 1;
|
|
}
|
|
if (err < 0)
|
|
return err;
|
|
else
|
|
err = 0;
|
|
|
|
/*
|
|
* The treatment of mapping from this point on is critical. The page
|
|
* lock protects many things but in this context the page lock
|
|
* stabilizes mapping, prevents inode freeing in the shared
|
|
* file-backed region case and guards against movement to swap cache.
|
|
*
|
|
* Strictly speaking the page lock is not needed in all cases being
|
|
* considered here and page lock forces unnecessarily serialization
|
|
* From this point on, mapping will be re-verified if necessary and
|
|
* page lock will be acquired only if it is unavoidable
|
|
*/
|
|
page = compound_head(page);
|
|
mapping = READ_ONCE(page->mapping);
|
|
|
|
/*
|
|
* If page->mapping is NULL, then it cannot be a PageAnon
|
|
* page; but it might be the ZERO_PAGE or in the gate area or
|
|
* in a special mapping (all cases which we are happy to fail);
|
|
* or it may have been a good file page when get_user_pages_fast
|
|
* found it, but truncated or holepunched or subjected to
|
|
* invalidate_complete_page2 before we got the page lock (also
|
|
* cases which we are happy to fail). And we hold a reference,
|
|
* so refcount care in invalidate_complete_page's remove_mapping
|
|
* prevents drop_caches from setting mapping to NULL beneath us.
|
|
*
|
|
* The case we do have to guard against is when memory pressure made
|
|
* shmem_writepage move it from filecache to swapcache beneath us:
|
|
* an unlikely race, but we do need to retry for page->mapping.
|
|
*/
|
|
if (unlikely(!mapping)) {
|
|
int shmem_swizzled;
|
|
|
|
/*
|
|
* Page lock is required to identify which special case above
|
|
* applies. If this is really a shmem page then the page lock
|
|
* will prevent unexpected transitions.
|
|
*/
|
|
lock_page(page);
|
|
shmem_swizzled = PageSwapCache(page) || page->mapping;
|
|
unlock_page(page);
|
|
put_page(page);
|
|
|
|
if (shmem_swizzled)
|
|
goto again;
|
|
|
|
return -EFAULT;
|
|
}
|
|
|
|
/*
|
|
* Private mappings are handled in a simple way.
|
|
*
|
|
* If the futex key is stored on an anonymous page, then the associated
|
|
* object is the mm which is implicitly pinned by the calling process.
|
|
*
|
|
* NOTE: When userspace waits on a MAP_SHARED mapping, even if
|
|
* it's a read-only handle, it's expected that futexes attach to
|
|
* the object not the particular process.
|
|
*/
|
|
if (PageAnon(page)) {
|
|
/*
|
|
* A RO anonymous page will never change and thus doesn't make
|
|
* sense for futex operations.
|
|
*/
|
|
if (unlikely(should_fail_futex(fshared)) || ro) {
|
|
err = -EFAULT;
|
|
goto out;
|
|
}
|
|
|
|
key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
|
|
key->private.mm = mm;
|
|
key->private.address = address;
|
|
|
|
get_futex_key_refs(key); /* implies smp_mb(); (B) */
|
|
|
|
} else {
|
|
struct inode *inode;
|
|
|
|
/*
|
|
* The associated futex object in this case is the inode and
|
|
* the page->mapping must be traversed. Ordinarily this should
|
|
* be stabilised under page lock but it's not strictly
|
|
* necessary in this case as we just want to pin the inode, not
|
|
* update the radix tree or anything like that.
|
|
*
|
|
* The RCU read lock is taken as the inode is finally freed
|
|
* under RCU. If the mapping still matches expectations then the
|
|
* mapping->host can be safely accessed as being a valid inode.
|
|
*/
|
|
rcu_read_lock();
|
|
|
|
if (READ_ONCE(page->mapping) != mapping) {
|
|
rcu_read_unlock();
|
|
put_page(page);
|
|
|
|
goto again;
|
|
}
|
|
|
|
inode = READ_ONCE(mapping->host);
|
|
if (!inode) {
|
|
rcu_read_unlock();
|
|
put_page(page);
|
|
|
|
goto again;
|
|
}
|
|
|
|
/*
|
|
* Take a reference unless it is about to be freed. Previously
|
|
* this reference was taken by ihold under the page lock
|
|
* pinning the inode in place so i_lock was unnecessary. The
|
|
* only way for this check to fail is if the inode was
|
|
* truncated in parallel so warn for now if this happens.
|
|
*
|
|
* We are not calling into get_futex_key_refs() in file-backed
|
|
* cases, therefore a successful atomic_inc return below will
|
|
* guarantee that get_futex_key() will still imply smp_mb(); (B).
|
|
*/
|
|
if (WARN_ON_ONCE(!atomic_inc_not_zero(&inode->i_count))) {
|
|
rcu_read_unlock();
|
|
put_page(page);
|
|
|
|
goto again;
|
|
}
|
|
|
|
/* Should be impossible but lets be paranoid for now */
|
|
if (WARN_ON_ONCE(inode->i_mapping != mapping)) {
|
|
err = -EFAULT;
|
|
rcu_read_unlock();
|
|
iput(inode);
|
|
|
|
goto out;
|
|
}
|
|
|
|
key->both.offset |= FUT_OFF_INODE; /* inode-based key */
|
|
key->shared.inode = inode;
|
|
key->shared.pgoff = basepage_index(page);
|
|
rcu_read_unlock();
|
|
}
|
|
|
|
out:
|
|
put_page(page);
|
|
return err;
|
|
}
|
|
|
|
static inline void put_futex_key(union futex_key *key)
|
|
{
|
|
drop_futex_key_refs(key);
|
|
}
|
|
|
|
/**
|
|
* fault_in_user_writeable() - Fault in user address and verify RW access
|
|
* @uaddr: pointer to faulting user space address
|
|
*
|
|
* Slow path to fixup the fault we just took in the atomic write
|
|
* access to @uaddr.
|
|
*
|
|
* We have no generic implementation of a non-destructive write to the
|
|
* user address. We know that we faulted in the atomic pagefault
|
|
* disabled section so we can as well avoid the #PF overhead by
|
|
* calling get_user_pages() right away.
|
|
*/
|
|
static int fault_in_user_writeable(u32 __user *uaddr)
|
|
{
|
|
struct mm_struct *mm = current->mm;
|
|
int ret;
|
|
|
|
down_read(&mm->mmap_sem);
|
|
ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
|
|
FAULT_FLAG_WRITE, NULL);
|
|
up_read(&mm->mmap_sem);
|
|
|
|
return ret < 0 ? ret : 0;
|
|
}
|
|
|
|
/**
|
|
* futex_top_waiter() - Return the highest priority waiter on a futex
|
|
* @hb: the hash bucket the futex_q's reside in
|
|
* @key: the futex key (to distinguish it from other futex futex_q's)
|
|
*
|
|
* Must be called with the hb lock held.
|
|
*/
|
|
static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
|
|
union futex_key *key)
|
|
{
|
|
struct futex_q *this;
|
|
|
|
plist_for_each_entry(this, &hb->chain, list) {
|
|
if (match_futex(&this->key, key))
|
|
return this;
|
|
}
|
|
return NULL;
|
|
}
|
|
|
|
static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
|
|
u32 uval, u32 newval)
|
|
{
|
|
int ret;
|
|
|
|
pagefault_disable();
|
|
ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
|
|
pagefault_enable();
|
|
|
|
return ret;
|
|
}
|
|
|
|
static int get_futex_value_locked(u32 *dest, u32 __user *from)
|
|
{
|
|
int ret;
|
|
|
|
pagefault_disable();
|
|
ret = __get_user(*dest, from);
|
|
pagefault_enable();
|
|
|
|
return ret ? -EFAULT : 0;
|
|
}
|
|
|
|
|
|
/*
|
|
* PI code:
|
|
*/
|
|
static int refill_pi_state_cache(void)
|
|
{
|
|
struct futex_pi_state *pi_state;
|
|
|
|
if (likely(current->pi_state_cache))
|
|
return 0;
|
|
|
|
pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
|
|
|
|
if (!pi_state)
|
|
return -ENOMEM;
|
|
|
|
INIT_LIST_HEAD(&pi_state->list);
|
|
/* pi_mutex gets initialized later */
|
|
pi_state->owner = NULL;
|
|
atomic_set(&pi_state->refcount, 1);
|
|
pi_state->key = FUTEX_KEY_INIT;
|
|
|
|
current->pi_state_cache = pi_state;
|
|
|
|
return 0;
|
|
}
|
|
|
|
static struct futex_pi_state * alloc_pi_state(void)
|
|
{
|
|
struct futex_pi_state *pi_state = current->pi_state_cache;
|
|
|
|
WARN_ON(!pi_state);
|
|
current->pi_state_cache = NULL;
|
|
|
|
return pi_state;
|
|
}
|
|
|
|
/*
|
|
* Drops a reference to the pi_state object and frees or caches it
|
|
* when the last reference is gone.
|
|
*
|
|
* Must be called with the hb lock held.
|
|
*/
|
|
static void put_pi_state(struct futex_pi_state *pi_state)
|
|
{
|
|
if (!pi_state)
|
|
return;
|
|
|
|
if (!atomic_dec_and_test(&pi_state->refcount))
|
|
return;
|
|
|
|
/*
|
|
* If pi_state->owner is NULL, the owner is most probably dying
|
|
* and has cleaned up the pi_state already
|
|
*/
|
|
if (pi_state->owner) {
|
|
raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
|
list_del_init(&pi_state->list);
|
|
raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
|
|
|
rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
|
|
}
|
|
|
|
if (current->pi_state_cache)
|
|
kfree(pi_state);
|
|
else {
|
|
/*
|
|
* pi_state->list is already empty.
|
|
* clear pi_state->owner.
|
|
* refcount is at 0 - put it back to 1.
|
|
*/
|
|
pi_state->owner = NULL;
|
|
atomic_set(&pi_state->refcount, 1);
|
|
current->pi_state_cache = pi_state;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Look up the task based on what TID userspace gave us.
|
|
* We dont trust it.
|
|
*/
|
|
static struct task_struct * futex_find_get_task(pid_t pid)
|
|
{
|
|
struct task_struct *p;
|
|
|
|
rcu_read_lock();
|
|
p = find_task_by_vpid(pid);
|
|
if (p)
|
|
get_task_struct(p);
|
|
|
|
rcu_read_unlock();
|
|
|
|
return p;
|
|
}
|
|
|
|
/*
|
|
* This task is holding PI mutexes at exit time => bad.
|
|
* Kernel cleans up PI-state, but userspace is likely hosed.
|
|
* (Robust-futex cleanup is separate and might save the day for userspace.)
|
|
*/
|
|
void exit_pi_state_list(struct task_struct *curr)
|
|
{
|
|
struct list_head *next, *head = &curr->pi_state_list;
|
|
struct futex_pi_state *pi_state;
|
|
struct futex_hash_bucket *hb;
|
|
union futex_key key = FUTEX_KEY_INIT;
|
|
|
|
if (!futex_cmpxchg_enabled)
|
|
return;
|
|
/*
|
|
* We are a ZOMBIE and nobody can enqueue itself on
|
|
* pi_state_list anymore, but we have to be careful
|
|
* versus waiters unqueueing themselves:
|
|
*/
|
|
raw_spin_lock_irq(&curr->pi_lock);
|
|
while (!list_empty(head)) {
|
|
|
|
next = head->next;
|
|
pi_state = list_entry(next, struct futex_pi_state, list);
|
|
key = pi_state->key;
|
|
hb = hash_futex(&key);
|
|
raw_spin_unlock_irq(&curr->pi_lock);
|
|
|
|
spin_lock(&hb->lock);
|
|
|
|
raw_spin_lock_irq(&curr->pi_lock);
|
|
/*
|
|
* We dropped the pi-lock, so re-check whether this
|
|
* task still owns the PI-state:
|
|
*/
|
|
if (head->next != next) {
|
|
spin_unlock(&hb->lock);
|
|
continue;
|
|
}
|
|
|
|
WARN_ON(pi_state->owner != curr);
|
|
WARN_ON(list_empty(&pi_state->list));
|
|
list_del_init(&pi_state->list);
|
|
pi_state->owner = NULL;
|
|
raw_spin_unlock_irq(&curr->pi_lock);
|
|
|
|
rt_mutex_unlock(&pi_state->pi_mutex);
|
|
|
|
spin_unlock(&hb->lock);
|
|
|
|
raw_spin_lock_irq(&curr->pi_lock);
|
|
}
|
|
raw_spin_unlock_irq(&curr->pi_lock);
|
|
}
|
|
|
|
/*
|
|
* We need to check the following states:
|
|
*
|
|
* Waiter | pi_state | pi->owner | uTID | uODIED | ?
|
|
*
|
|
* [1] NULL | --- | --- | 0 | 0/1 | Valid
|
|
* [2] NULL | --- | --- | >0 | 0/1 | Valid
|
|
*
|
|
* [3] Found | NULL | -- | Any | 0/1 | Invalid
|
|
*
|
|
* [4] Found | Found | NULL | 0 | 1 | Valid
|
|
* [5] Found | Found | NULL | >0 | 1 | Invalid
|
|
*
|
|
* [6] Found | Found | task | 0 | 1 | Valid
|
|
*
|
|
* [7] Found | Found | NULL | Any | 0 | Invalid
|
|
*
|
|
* [8] Found | Found | task | ==taskTID | 0/1 | Valid
|
|
* [9] Found | Found | task | 0 | 0 | Invalid
|
|
* [10] Found | Found | task | !=taskTID | 0/1 | Invalid
|
|
*
|
|
* [1] Indicates that the kernel can acquire the futex atomically. We
|
|
* came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
|
|
*
|
|
* [2] Valid, if TID does not belong to a kernel thread. If no matching
|
|
* thread is found then it indicates that the owner TID has died.
|
|
*
|
|
* [3] Invalid. The waiter is queued on a non PI futex
|
|
*
|
|
* [4] Valid state after exit_robust_list(), which sets the user space
|
|
* value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
|
|
*
|
|
* [5] The user space value got manipulated between exit_robust_list()
|
|
* and exit_pi_state_list()
|
|
*
|
|
* [6] Valid state after exit_pi_state_list() which sets the new owner in
|
|
* the pi_state but cannot access the user space value.
|
|
*
|
|
* [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
|
|
*
|
|
* [8] Owner and user space value match
|
|
*
|
|
* [9] There is no transient state which sets the user space TID to 0
|
|
* except exit_robust_list(), but this is indicated by the
|
|
* FUTEX_OWNER_DIED bit. See [4]
|
|
*
|
|
* [10] There is no transient state which leaves owner and user space
|
|
* TID out of sync.
|
|
*/
|
|
|
|
/*
|
|
* Validate that the existing waiter has a pi_state and sanity check
|
|
* the pi_state against the user space value. If correct, attach to
|
|
* it.
|
|
*/
|
|
static int attach_to_pi_state(u32 uval, struct futex_pi_state *pi_state,
|
|
struct futex_pi_state **ps)
|
|
{
|
|
pid_t pid = uval & FUTEX_TID_MASK;
|
|
|
|
/*
|
|
* Userspace might have messed up non-PI and PI futexes [3]
|
|
*/
|
|
if (unlikely(!pi_state))
|
|
return -EINVAL;
|
|
|
|
WARN_ON(!atomic_read(&pi_state->refcount));
|
|
|
|
/*
|
|
* Handle the owner died case:
|
|
*/
|
|
if (uval & FUTEX_OWNER_DIED) {
|
|
/*
|
|
* exit_pi_state_list sets owner to NULL and wakes the
|
|
* topmost waiter. The task which acquires the
|
|
* pi_state->rt_mutex will fixup owner.
|
|
*/
|
|
if (!pi_state->owner) {
|
|
/*
|
|
* No pi state owner, but the user space TID
|
|
* is not 0. Inconsistent state. [5]
|
|
*/
|
|
if (pid)
|
|
return -EINVAL;
|
|
/*
|
|
* Take a ref on the state and return success. [4]
|
|
*/
|
|
goto out_state;
|
|
}
|
|
|
|
/*
|
|
* If TID is 0, then either the dying owner has not
|
|
* yet executed exit_pi_state_list() or some waiter
|
|
* acquired the rtmutex in the pi state, but did not
|
|
* yet fixup the TID in user space.
|
|
*
|
|
* Take a ref on the state and return success. [6]
|
|
*/
|
|
if (!pid)
|
|
goto out_state;
|
|
} else {
|
|
/*
|
|
* If the owner died bit is not set, then the pi_state
|
|
* must have an owner. [7]
|
|
*/
|
|
if (!pi_state->owner)
|
|
return -EINVAL;
|
|
}
|
|
|
|
/*
|
|
* Bail out if user space manipulated the futex value. If pi
|
|
* state exists then the owner TID must be the same as the
|
|
* user space TID. [9/10]
|
|
*/
|
|
if (pid != task_pid_vnr(pi_state->owner))
|
|
return -EINVAL;
|
|
out_state:
|
|
atomic_inc(&pi_state->refcount);
|
|
*ps = pi_state;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Lookup the task for the TID provided from user space and attach to
|
|
* it after doing proper sanity checks.
|
|
*/
|
|
static int attach_to_pi_owner(u32 uval, union futex_key *key,
|
|
struct futex_pi_state **ps)
|
|
{
|
|
pid_t pid = uval & FUTEX_TID_MASK;
|
|
struct futex_pi_state *pi_state;
|
|
struct task_struct *p;
|
|
|
|
/*
|
|
* We are the first waiter - try to look up the real owner and attach
|
|
* the new pi_state to it, but bail out when TID = 0 [1]
|
|
*/
|
|
if (!pid)
|
|
return -ESRCH;
|
|
p = futex_find_get_task(pid);
|
|
if (!p)
|
|
return -ESRCH;
|
|
|
|
if (unlikely(p->flags & PF_KTHREAD)) {
|
|
put_task_struct(p);
|
|
return -EPERM;
|
|
}
|
|
|
|
/*
|
|
* We need to look at the task state flags to figure out,
|
|
* whether the task is exiting. To protect against the do_exit
|
|
* change of the task flags, we do this protected by
|
|
* p->pi_lock:
|
|
*/
|
|
raw_spin_lock_irq(&p->pi_lock);
|
|
if (unlikely(p->flags & PF_EXITING)) {
|
|
/*
|
|
* The task is on the way out. When PF_EXITPIDONE is
|
|
* set, we know that the task has finished the
|
|
* cleanup:
|
|
*/
|
|
int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
|
|
|
|
raw_spin_unlock_irq(&p->pi_lock);
|
|
put_task_struct(p);
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* No existing pi state. First waiter. [2]
|
|
*/
|
|
pi_state = alloc_pi_state();
|
|
|
|
/*
|
|
* Initialize the pi_mutex in locked state and make @p
|
|
* the owner of it:
|
|
*/
|
|
rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
|
|
|
|
/* Store the key for possible exit cleanups: */
|
|
pi_state->key = *key;
|
|
|
|
WARN_ON(!list_empty(&pi_state->list));
|
|
list_add(&pi_state->list, &p->pi_state_list);
|
|
pi_state->owner = p;
|
|
raw_spin_unlock_irq(&p->pi_lock);
|
|
|
|
put_task_struct(p);
|
|
|
|
*ps = pi_state;
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
|
|
union futex_key *key, struct futex_pi_state **ps)
|
|
{
|
|
struct futex_q *match = futex_top_waiter(hb, key);
|
|
|
|
/*
|
|
* If there is a waiter on that futex, validate it and
|
|
* attach to the pi_state when the validation succeeds.
|
|
*/
|
|
if (match)
|
|
return attach_to_pi_state(uval, match->pi_state, ps);
|
|
|
|
/*
|
|
* We are the first waiter - try to look up the owner based on
|
|
* @uval and attach to it.
|
|
*/
|
|
return attach_to_pi_owner(uval, key, ps);
|
|
}
|
|
|
|
static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
|
|
{
|
|
u32 uninitialized_var(curval);
|
|
|
|
if (unlikely(should_fail_futex(true)))
|
|
return -EFAULT;
|
|
|
|
if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
|
|
return -EFAULT;
|
|
|
|
/*If user space value changed, let the caller retry */
|
|
return curval != uval ? -EAGAIN : 0;
|
|
}
|
|
|
|
/**
|
|
* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
|
|
* @uaddr: the pi futex user address
|
|
* @hb: the pi futex hash bucket
|
|
* @key: the futex key associated with uaddr and hb
|
|
* @ps: the pi_state pointer where we store the result of the
|
|
* lookup
|
|
* @task: the task to perform the atomic lock work for. This will
|
|
* be "current" except in the case of requeue pi.
|
|
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
|
*
|
|
* Return:
|
|
* 0 - ready to wait;
|
|
* 1 - acquired the lock;
|
|
* <0 - error
|
|
*
|
|
* The hb->lock and futex_key refs shall be held by the caller.
|
|
*/
|
|
static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
|
|
union futex_key *key,
|
|
struct futex_pi_state **ps,
|
|
struct task_struct *task, int set_waiters)
|
|
{
|
|
u32 uval, newval, vpid = task_pid_vnr(task);
|
|
struct futex_q *match;
|
|
int ret;
|
|
|
|
/*
|
|
* Read the user space value first so we can validate a few
|
|
* things before proceeding further.
|
|
*/
|
|
if (get_futex_value_locked(&uval, uaddr))
|
|
return -EFAULT;
|
|
|
|
if (unlikely(should_fail_futex(true)))
|
|
return -EFAULT;
|
|
|
|
/*
|
|
* Detect deadlocks.
|
|
*/
|
|
if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
|
|
return -EDEADLK;
|
|
|
|
if ((unlikely(should_fail_futex(true))))
|
|
return -EDEADLK;
|
|
|
|
/*
|
|
* Lookup existing state first. If it exists, try to attach to
|
|
* its pi_state.
|
|
*/
|
|
match = futex_top_waiter(hb, key);
|
|
if (match)
|
|
return attach_to_pi_state(uval, match->pi_state, ps);
|
|
|
|
/*
|
|
* No waiter and user TID is 0. We are here because the
|
|
* waiters or the owner died bit is set or called from
|
|
* requeue_cmp_pi or for whatever reason something took the
|
|
* syscall.
|
|
*/
|
|
if (!(uval & FUTEX_TID_MASK)) {
|
|
/*
|
|
* We take over the futex. No other waiters and the user space
|
|
* TID is 0. We preserve the owner died bit.
|
|
*/
|
|
newval = uval & FUTEX_OWNER_DIED;
|
|
newval |= vpid;
|
|
|
|
/* The futex requeue_pi code can enforce the waiters bit */
|
|
if (set_waiters)
|
|
newval |= FUTEX_WAITERS;
|
|
|
|
ret = lock_pi_update_atomic(uaddr, uval, newval);
|
|
/* If the take over worked, return 1 */
|
|
return ret < 0 ? ret : 1;
|
|
}
|
|
|
|
/*
|
|
* First waiter. Set the waiters bit before attaching ourself to
|
|
* the owner. If owner tries to unlock, it will be forced into
|
|
* the kernel and blocked on hb->lock.
|
|
*/
|
|
newval = uval | FUTEX_WAITERS;
|
|
ret = lock_pi_update_atomic(uaddr, uval, newval);
|
|
if (ret)
|
|
return ret;
|
|
/*
|
|
* If the update of the user space value succeeded, we try to
|
|
* attach to the owner. If that fails, no harm done, we only
|
|
* set the FUTEX_WAITERS bit in the user space variable.
|
|
*/
|
|
return attach_to_pi_owner(uval, key, ps);
|
|
}
|
|
|
|
/**
|
|
* __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
|
|
* @q: The futex_q to unqueue
|
|
*
|
|
* The q->lock_ptr must not be NULL and must be held by the caller.
|
|
*/
|
|
static void __unqueue_futex(struct futex_q *q)
|
|
{
|
|
struct futex_hash_bucket *hb;
|
|
|
|
if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
|
|
|| WARN_ON(plist_node_empty(&q->list)))
|
|
return;
|
|
|
|
hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
|
|
plist_del(&q->list, &hb->chain);
|
|
hb_waiters_dec(hb);
|
|
}
|
|
|
|
/*
|
|
* The hash bucket lock must be held when this is called.
|
|
* Afterwards, the futex_q must not be accessed. Callers
|
|
* must ensure to later call wake_up_q() for the actual
|
|
* wakeups to occur.
|
|
*/
|
|
static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
|
|
{
|
|
struct task_struct *p = q->task;
|
|
|
|
if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
|
|
return;
|
|
|
|
/*
|
|
* Queue the task for later wakeup for after we've released
|
|
* the hb->lock. wake_q_add() grabs reference to p.
|
|
*/
|
|
wake_q_add(wake_q, p);
|
|
__unqueue_futex(q);
|
|
/*
|
|
* The waiting task can free the futex_q as soon as
|
|
* q->lock_ptr = NULL is written, without taking any locks. A
|
|
* memory barrier is required here to prevent the following
|
|
* store to lock_ptr from getting ahead of the plist_del.
|
|
*/
|
|
smp_wmb();
|
|
q->lock_ptr = NULL;
|
|
}
|
|
|
|
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this,
|
|
struct futex_hash_bucket *hb)
|
|
{
|
|
struct task_struct *new_owner;
|
|
struct futex_pi_state *pi_state = this->pi_state;
|
|
u32 uninitialized_var(curval), newval;
|
|
WAKE_Q(wake_q);
|
|
bool deboost;
|
|
int ret = 0;
|
|
|
|
if (!pi_state)
|
|
return -EINVAL;
|
|
|
|
/*
|
|
* If current does not own the pi_state then the futex is
|
|
* inconsistent and user space fiddled with the futex value.
|
|
*/
|
|
if (pi_state->owner != current)
|
|
return -EINVAL;
|
|
|
|
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
|
|
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
|
|
|
|
/*
|
|
* It is possible that the next waiter (the one that brought
|
|
* this owner to the kernel) timed out and is no longer
|
|
* waiting on the lock.
|
|
*/
|
|
if (!new_owner)
|
|
new_owner = this->task;
|
|
|
|
/*
|
|
* We pass it to the next owner. The WAITERS bit is always
|
|
* kept enabled while there is PI state around. We cleanup the
|
|
* owner died bit, because we are the owner.
|
|
*/
|
|
newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
|
|
|
|
if (unlikely(should_fail_futex(true)))
|
|
ret = -EFAULT;
|
|
|
|
if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
|
|
ret = -EFAULT;
|
|
} else if (curval != uval) {
|
|
/*
|
|
* If a unconditional UNLOCK_PI operation (user space did not
|
|
* try the TID->0 transition) raced with a waiter setting the
|
|
* FUTEX_WAITERS flag between get_user() and locking the hash
|
|
* bucket lock, retry the operation.
|
|
*/
|
|
if ((FUTEX_TID_MASK & curval) == uval)
|
|
ret = -EAGAIN;
|
|
else
|
|
ret = -EINVAL;
|
|
}
|
|
if (ret) {
|
|
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
|
return ret;
|
|
}
|
|
|
|
raw_spin_lock(&pi_state->owner->pi_lock);
|
|
WARN_ON(list_empty(&pi_state->list));
|
|
list_del_init(&pi_state->list);
|
|
raw_spin_unlock(&pi_state->owner->pi_lock);
|
|
|
|
raw_spin_lock(&new_owner->pi_lock);
|
|
WARN_ON(!list_empty(&pi_state->list));
|
|
list_add(&pi_state->list, &new_owner->pi_state_list);
|
|
pi_state->owner = new_owner;
|
|
raw_spin_unlock(&new_owner->pi_lock);
|
|
|
|
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
|
|
|
|
deboost = rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
|
|
|
|
/*
|
|
* First unlock HB so the waiter does not spin on it once he got woken
|
|
* up. Second wake up the waiter before the priority is adjusted. If we
|
|
* deboost first (and lose our higher priority), then the task might get
|
|
* scheduled away before the wake up can take place.
|
|
*/
|
|
spin_unlock(&hb->lock);
|
|
wake_up_q(&wake_q);
|
|
if (deboost)
|
|
rt_mutex_adjust_prio(current);
|
|
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Express the locking dependencies for lockdep:
|
|
*/
|
|
static inline void
|
|
double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
|
{
|
|
if (hb1 <= hb2) {
|
|
spin_lock(&hb1->lock);
|
|
if (hb1 < hb2)
|
|
spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
|
|
} else { /* hb1 > hb2 */
|
|
spin_lock(&hb2->lock);
|
|
spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
|
|
}
|
|
}
|
|
|
|
static inline void
|
|
double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
|
{
|
|
spin_unlock(&hb1->lock);
|
|
if (hb1 != hb2)
|
|
spin_unlock(&hb2->lock);
|
|
}
|
|
|
|
/*
|
|
* Wake up waiters matching bitset queued on this futex (uaddr).
|
|
*/
|
|
static int
|
|
futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
|
|
{
|
|
struct futex_hash_bucket *hb;
|
|
struct futex_q *this, *next;
|
|
union futex_key key = FUTEX_KEY_INIT;
|
|
int ret;
|
|
WAKE_Q(wake_q);
|
|
|
|
if (!bitset)
|
|
return -EINVAL;
|
|
|
|
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
hb = hash_futex(&key);
|
|
|
|
/* Make sure we really have tasks to wakeup */
|
|
if (!hb_waiters_pending(hb))
|
|
goto out_put_key;
|
|
|
|
spin_lock(&hb->lock);
|
|
|
|
plist_for_each_entry_safe(this, next, &hb->chain, list) {
|
|
if (match_futex (&this->key, &key)) {
|
|
if (this->pi_state || this->rt_waiter) {
|
|
ret = -EINVAL;
|
|
break;
|
|
}
|
|
|
|
/* Check if one of the bits is set in both bitsets */
|
|
if (!(this->bitset & bitset))
|
|
continue;
|
|
|
|
mark_wake_futex(&wake_q, this);
|
|
if (++ret >= nr_wake)
|
|
break;
|
|
}
|
|
}
|
|
|
|
spin_unlock(&hb->lock);
|
|
wake_up_q(&wake_q);
|
|
out_put_key:
|
|
put_futex_key(&key);
|
|
out:
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Wake up all waiters hashed on the physical page that is mapped
|
|
* to this virtual address:
|
|
*/
|
|
static int
|
|
futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
|
|
int nr_wake, int nr_wake2, int op)
|
|
{
|
|
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
|
struct futex_hash_bucket *hb1, *hb2;
|
|
struct futex_q *this, *next;
|
|
int ret, op_ret;
|
|
WAKE_Q(wake_q);
|
|
|
|
retry:
|
|
ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
|
|
if (unlikely(ret != 0))
|
|
goto out_put_key1;
|
|
|
|
hb1 = hash_futex(&key1);
|
|
hb2 = hash_futex(&key2);
|
|
|
|
retry_private:
|
|
double_lock_hb(hb1, hb2);
|
|
op_ret = futex_atomic_op_inuser(op, uaddr2);
|
|
if (unlikely(op_ret < 0)) {
|
|
|
|
double_unlock_hb(hb1, hb2);
|
|
|
|
#ifndef CONFIG_MMU
|
|
/*
|
|
* we don't get EFAULT from MMU faults if we don't have an MMU,
|
|
* but we might get them from range checking
|
|
*/
|
|
ret = op_ret;
|
|
goto out_put_keys;
|
|
#endif
|
|
|
|
if (unlikely(op_ret != -EFAULT)) {
|
|
ret = op_ret;
|
|
goto out_put_keys;
|
|
}
|
|
|
|
ret = fault_in_user_writeable(uaddr2);
|
|
if (ret)
|
|
goto out_put_keys;
|
|
|
|
if (!(flags & FLAGS_SHARED))
|
|
goto retry_private;
|
|
|
|
put_futex_key(&key2);
|
|
put_futex_key(&key1);
|
|
goto retry;
|
|
}
|
|
|
|
plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
|
if (match_futex (&this->key, &key1)) {
|
|
if (this->pi_state || this->rt_waiter) {
|
|
ret = -EINVAL;
|
|
goto out_unlock;
|
|
}
|
|
mark_wake_futex(&wake_q, this);
|
|
if (++ret >= nr_wake)
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (op_ret > 0) {
|
|
op_ret = 0;
|
|
plist_for_each_entry_safe(this, next, &hb2->chain, list) {
|
|
if (match_futex (&this->key, &key2)) {
|
|
if (this->pi_state || this->rt_waiter) {
|
|
ret = -EINVAL;
|
|
goto out_unlock;
|
|
}
|
|
mark_wake_futex(&wake_q, this);
|
|
if (++op_ret >= nr_wake2)
|
|
break;
|
|
}
|
|
}
|
|
ret += op_ret;
|
|
}
|
|
|
|
out_unlock:
|
|
double_unlock_hb(hb1, hb2);
|
|
wake_up_q(&wake_q);
|
|
out_put_keys:
|
|
put_futex_key(&key2);
|
|
out_put_key1:
|
|
put_futex_key(&key1);
|
|
out:
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* requeue_futex() - Requeue a futex_q from one hb to another
|
|
* @q: the futex_q to requeue
|
|
* @hb1: the source hash_bucket
|
|
* @hb2: the target hash_bucket
|
|
* @key2: the new key for the requeued futex_q
|
|
*/
|
|
static inline
|
|
void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
|
|
struct futex_hash_bucket *hb2, union futex_key *key2)
|
|
{
|
|
|
|
/*
|
|
* If key1 and key2 hash to the same bucket, no need to
|
|
* requeue.
|
|
*/
|
|
if (likely(&hb1->chain != &hb2->chain)) {
|
|
plist_del(&q->list, &hb1->chain);
|
|
hb_waiters_dec(hb1);
|
|
hb_waiters_inc(hb2);
|
|
plist_add(&q->list, &hb2->chain);
|
|
q->lock_ptr = &hb2->lock;
|
|
}
|
|
get_futex_key_refs(key2);
|
|
q->key = *key2;
|
|
}
|
|
|
|
/**
|
|
* requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
|
|
* @q: the futex_q
|
|
* @key: the key of the requeue target futex
|
|
* @hb: the hash_bucket of the requeue target futex
|
|
*
|
|
* During futex_requeue, with requeue_pi=1, it is possible to acquire the
|
|
* target futex if it is uncontended or via a lock steal. Set the futex_q key
|
|
* to the requeue target futex so the waiter can detect the wakeup on the right
|
|
* futex, but remove it from the hb and NULL the rt_waiter so it can detect
|
|
* atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
|
|
* to protect access to the pi_state to fixup the owner later. Must be called
|
|
* with both q->lock_ptr and hb->lock held.
|
|
*/
|
|
static inline
|
|
void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
|
|
struct futex_hash_bucket *hb)
|
|
{
|
|
get_futex_key_refs(key);
|
|
q->key = *key;
|
|
|
|
__unqueue_futex(q);
|
|
|
|
WARN_ON(!q->rt_waiter);
|
|
q->rt_waiter = NULL;
|
|
|
|
q->lock_ptr = &hb->lock;
|
|
|
|
wake_up_state(q->task, TASK_NORMAL);
|
|
}
|
|
|
|
/**
|
|
* futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
|
|
* @pifutex: the user address of the to futex
|
|
* @hb1: the from futex hash bucket, must be locked by the caller
|
|
* @hb2: the to futex hash bucket, must be locked by the caller
|
|
* @key1: the from futex key
|
|
* @key2: the to futex key
|
|
* @ps: address to store the pi_state pointer
|
|
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
|
*
|
|
* Try and get the lock on behalf of the top waiter if we can do it atomically.
|
|
* Wake the top waiter if we succeed. If the caller specified set_waiters,
|
|
* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
|
|
* hb1 and hb2 must be held by the caller.
|
|
*
|
|
* Return:
|
|
* 0 - failed to acquire the lock atomically;
|
|
* >0 - acquired the lock, return value is vpid of the top_waiter
|
|
* <0 - error
|
|
*/
|
|
static int futex_proxy_trylock_atomic(u32 __user *pifutex,
|
|
struct futex_hash_bucket *hb1,
|
|
struct futex_hash_bucket *hb2,
|
|
union futex_key *key1, union futex_key *key2,
|
|
struct futex_pi_state **ps, int set_waiters)
|
|
{
|
|
struct futex_q *top_waiter = NULL;
|
|
u32 curval;
|
|
int ret, vpid;
|
|
|
|
if (get_futex_value_locked(&curval, pifutex))
|
|
return -EFAULT;
|
|
|
|
if (unlikely(should_fail_futex(true)))
|
|
return -EFAULT;
|
|
|
|
/*
|
|
* Find the top_waiter and determine if there are additional waiters.
|
|
* If the caller intends to requeue more than 1 waiter to pifutex,
|
|
* force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
|
|
* as we have means to handle the possible fault. If not, don't set
|
|
* the bit unecessarily as it will force the subsequent unlock to enter
|
|
* the kernel.
|
|
*/
|
|
top_waiter = futex_top_waiter(hb1, key1);
|
|
|
|
/* There are no waiters, nothing for us to do. */
|
|
if (!top_waiter)
|
|
return 0;
|
|
|
|
/* Ensure we requeue to the expected futex. */
|
|
if (!match_futex(top_waiter->requeue_pi_key, key2))
|
|
return -EINVAL;
|
|
|
|
/*
|
|
* Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
|
|
* the contended case or if set_waiters is 1. The pi_state is returned
|
|
* in ps in contended cases.
|
|
*/
|
|
vpid = task_pid_vnr(top_waiter->task);
|
|
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
|
|
set_waiters);
|
|
if (ret == 1) {
|
|
requeue_pi_wake_futex(top_waiter, key2, hb2);
|
|
return vpid;
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* futex_requeue() - Requeue waiters from uaddr1 to uaddr2
|
|
* @uaddr1: source futex user address
|
|
* @flags: futex flags (FLAGS_SHARED, etc.)
|
|
* @uaddr2: target futex user address
|
|
* @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
|
|
* @nr_requeue: number of waiters to requeue (0-INT_MAX)
|
|
* @cmpval: @uaddr1 expected value (or %NULL)
|
|
* @requeue_pi: if we are attempting to requeue from a non-pi futex to a
|
|
* pi futex (pi to pi requeue is not supported)
|
|
*
|
|
* Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
|
|
* uaddr2 atomically on behalf of the top waiter.
|
|
*
|
|
* Return:
|
|
* >=0 - on success, the number of tasks requeued or woken;
|
|
* <0 - on error
|
|
*/
|
|
static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
|
|
u32 __user *uaddr2, int nr_wake, int nr_requeue,
|
|
u32 *cmpval, int requeue_pi)
|
|
{
|
|
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
|
int drop_count = 0, task_count = 0, ret;
|
|
struct futex_pi_state *pi_state = NULL;
|
|
struct futex_hash_bucket *hb1, *hb2;
|
|
struct futex_q *this, *next;
|
|
WAKE_Q(wake_q);
|
|
|
|
if (requeue_pi) {
|
|
/*
|
|
* Requeue PI only works on two distinct uaddrs. This
|
|
* check is only valid for private futexes. See below.
|
|
*/
|
|
if (uaddr1 == uaddr2)
|
|
return -EINVAL;
|
|
|
|
/*
|
|
* requeue_pi requires a pi_state, try to allocate it now
|
|
* without any locks in case it fails.
|
|
*/
|
|
if (refill_pi_state_cache())
|
|
return -ENOMEM;
|
|
/*
|
|
* requeue_pi must wake as many tasks as it can, up to nr_wake
|
|
* + nr_requeue, since it acquires the rt_mutex prior to
|
|
* returning to userspace, so as to not leave the rt_mutex with
|
|
* waiters and no owner. However, second and third wake-ups
|
|
* cannot be predicted as they involve race conditions with the
|
|
* first wake and a fault while looking up the pi_state. Both
|
|
* pthread_cond_signal() and pthread_cond_broadcast() should
|
|
* use nr_wake=1.
|
|
*/
|
|
if (nr_wake != 1)
|
|
return -EINVAL;
|
|
}
|
|
|
|
retry:
|
|
ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
|
|
requeue_pi ? VERIFY_WRITE : VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
goto out_put_key1;
|
|
|
|
/*
|
|
* The check above which compares uaddrs is not sufficient for
|
|
* shared futexes. We need to compare the keys:
|
|
*/
|
|
if (requeue_pi && match_futex(&key1, &key2)) {
|
|
ret = -EINVAL;
|
|
goto out_put_keys;
|
|
}
|
|
|
|
hb1 = hash_futex(&key1);
|
|
hb2 = hash_futex(&key2);
|
|
|
|
retry_private:
|
|
hb_waiters_inc(hb2);
|
|
double_lock_hb(hb1, hb2);
|
|
|
|
if (likely(cmpval != NULL)) {
|
|
u32 curval;
|
|
|
|
ret = get_futex_value_locked(&curval, uaddr1);
|
|
|
|
if (unlikely(ret)) {
|
|
double_unlock_hb(hb1, hb2);
|
|
hb_waiters_dec(hb2);
|
|
|
|
ret = get_user(curval, uaddr1);
|
|
if (ret)
|
|
goto out_put_keys;
|
|
|
|
if (!(flags & FLAGS_SHARED))
|
|
goto retry_private;
|
|
|
|
put_futex_key(&key2);
|
|
put_futex_key(&key1);
|
|
goto retry;
|
|
}
|
|
if (curval != *cmpval) {
|
|
ret = -EAGAIN;
|
|
goto out_unlock;
|
|
}
|
|
}
|
|
|
|
if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
|
|
/*
|
|
* Attempt to acquire uaddr2 and wake the top waiter. If we
|
|
* intend to requeue waiters, force setting the FUTEX_WAITERS
|
|
* bit. We force this here where we are able to easily handle
|
|
* faults rather in the requeue loop below.
|
|
*/
|
|
ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
|
|
&key2, &pi_state, nr_requeue);
|
|
|
|
/*
|
|
* At this point the top_waiter has either taken uaddr2 or is
|
|
* waiting on it. If the former, then the pi_state will not
|
|
* exist yet, look it up one more time to ensure we have a
|
|
* reference to it. If the lock was taken, ret contains the
|
|
* vpid of the top waiter task.
|
|
* If the lock was not taken, we have pi_state and an initial
|
|
* refcount on it. In case of an error we have nothing.
|
|
*/
|
|
if (ret > 0) {
|
|
WARN_ON(pi_state);
|
|
drop_count++;
|
|
task_count++;
|
|
/*
|
|
* If we acquired the lock, then the user space value
|
|
* of uaddr2 should be vpid. It cannot be changed by
|
|
* the top waiter as it is blocked on hb2 lock if it
|
|
* tries to do so. If something fiddled with it behind
|
|
* our back the pi state lookup might unearth it. So
|
|
* we rather use the known value than rereading and
|
|
* handing potential crap to lookup_pi_state.
|
|
*
|
|
* If that call succeeds then we have pi_state and an
|
|
* initial refcount on it.
|
|
*/
|
|
ret = lookup_pi_state(ret, hb2, &key2, &pi_state);
|
|
}
|
|
|
|
switch (ret) {
|
|
case 0:
|
|
/* We hold a reference on the pi state. */
|
|
break;
|
|
|
|
/* If the above failed, then pi_state is NULL */
|
|
case -EFAULT:
|
|
double_unlock_hb(hb1, hb2);
|
|
hb_waiters_dec(hb2);
|
|
put_futex_key(&key2);
|
|
put_futex_key(&key1);
|
|
ret = fault_in_user_writeable(uaddr2);
|
|
if (!ret)
|
|
goto retry;
|
|
goto out;
|
|
case -EAGAIN:
|
|
/*
|
|
* Two reasons for this:
|
|
* - Owner is exiting and we just wait for the
|
|
* exit to complete.
|
|
* - The user space value changed.
|
|
*/
|
|
double_unlock_hb(hb1, hb2);
|
|
hb_waiters_dec(hb2);
|
|
put_futex_key(&key2);
|
|
put_futex_key(&key1);
|
|
cond_resched();
|
|
goto retry;
|
|
default:
|
|
goto out_unlock;
|
|
}
|
|
}
|
|
|
|
plist_for_each_entry_safe(this, next, &hb1->chain, list) {
|
|
if (task_count - nr_wake >= nr_requeue)
|
|
break;
|
|
|
|
if (!match_futex(&this->key, &key1))
|
|
continue;
|
|
|
|
/*
|
|
* FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
|
|
* be paired with each other and no other futex ops.
|
|
*
|
|
* We should never be requeueing a futex_q with a pi_state,
|
|
* which is awaiting a futex_unlock_pi().
|
|
*/
|
|
if ((requeue_pi && !this->rt_waiter) ||
|
|
(!requeue_pi && this->rt_waiter) ||
|
|
this->pi_state) {
|
|
ret = -EINVAL;
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* Wake nr_wake waiters. For requeue_pi, if we acquired the
|
|
* lock, we already woke the top_waiter. If not, it will be
|
|
* woken by futex_unlock_pi().
|
|
*/
|
|
if (++task_count <= nr_wake && !requeue_pi) {
|
|
mark_wake_futex(&wake_q, this);
|
|
continue;
|
|
}
|
|
|
|
/* Ensure we requeue to the expected futex for requeue_pi. */
|
|
if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
|
|
ret = -EINVAL;
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* Requeue nr_requeue waiters and possibly one more in the case
|
|
* of requeue_pi if we couldn't acquire the lock atomically.
|
|
*/
|
|
if (requeue_pi) {
|
|
/*
|
|
* Prepare the waiter to take the rt_mutex. Take a
|
|
* refcount on the pi_state and store the pointer in
|
|
* the futex_q object of the waiter.
|
|
*/
|
|
atomic_inc(&pi_state->refcount);
|
|
this->pi_state = pi_state;
|
|
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
|
|
this->rt_waiter,
|
|
this->task);
|
|
if (ret == 1) {
|
|
/*
|
|
* We got the lock. We do neither drop the
|
|
* refcount on pi_state nor clear
|
|
* this->pi_state because the waiter needs the
|
|
* pi_state for cleaning up the user space
|
|
* value. It will drop the refcount after
|
|
* doing so.
|
|
*/
|
|
requeue_pi_wake_futex(this, &key2, hb2);
|
|
drop_count++;
|
|
continue;
|
|
} else if (ret) {
|
|
/*
|
|
* rt_mutex_start_proxy_lock() detected a
|
|
* potential deadlock when we tried to queue
|
|
* that waiter. Drop the pi_state reference
|
|
* which we took above and remove the pointer
|
|
* to the state from the waiters futex_q
|
|
* object.
|
|
*/
|
|
this->pi_state = NULL;
|
|
put_pi_state(pi_state);
|
|
/*
|
|
* We stop queueing more waiters and let user
|
|
* space deal with the mess.
|
|
*/
|
|
break;
|
|
}
|
|
}
|
|
requeue_futex(this, hb1, hb2, &key2);
|
|
drop_count++;
|
|
}
|
|
|
|
/*
|
|
* We took an extra initial reference to the pi_state either
|
|
* in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
|
|
* need to drop it here again.
|
|
*/
|
|
put_pi_state(pi_state);
|
|
|
|
out_unlock:
|
|
double_unlock_hb(hb1, hb2);
|
|
wake_up_q(&wake_q);
|
|
hb_waiters_dec(hb2);
|
|
|
|
/*
|
|
* drop_futex_key_refs() must be called outside the spinlocks. During
|
|
* the requeue we moved futex_q's from the hash bucket at key1 to the
|
|
* one at key2 and updated their key pointer. We no longer need to
|
|
* hold the references to key1.
|
|
*/
|
|
while (--drop_count >= 0)
|
|
drop_futex_key_refs(&key1);
|
|
|
|
out_put_keys:
|
|
put_futex_key(&key2);
|
|
out_put_key1:
|
|
put_futex_key(&key1);
|
|
out:
|
|
return ret ? ret : task_count;
|
|
}
|
|
|
|
/* The key must be already stored in q->key. */
|
|
static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
|
|
__acquires(&hb->lock)
|
|
{
|
|
struct futex_hash_bucket *hb;
|
|
|
|
hb = hash_futex(&q->key);
|
|
|
|
/*
|
|
* Increment the counter before taking the lock so that
|
|
* a potential waker won't miss a to-be-slept task that is
|
|
* waiting for the spinlock. This is safe as all queue_lock()
|
|
* users end up calling queue_me(). Similarly, for housekeeping,
|
|
* decrement the counter at queue_unlock() when some error has
|
|
* occurred and we don't end up adding the task to the list.
|
|
*/
|
|
hb_waiters_inc(hb);
|
|
|
|
q->lock_ptr = &hb->lock;
|
|
|
|
spin_lock(&hb->lock); /* implies smp_mb(); (A) */
|
|
return hb;
|
|
}
|
|
|
|
static inline void
|
|
queue_unlock(struct futex_hash_bucket *hb)
|
|
__releases(&hb->lock)
|
|
{
|
|
spin_unlock(&hb->lock);
|
|
hb_waiters_dec(hb);
|
|
}
|
|
|
|
/**
|
|
* queue_me() - Enqueue the futex_q on the futex_hash_bucket
|
|
* @q: The futex_q to enqueue
|
|
* @hb: The destination hash bucket
|
|
*
|
|
* The hb->lock must be held by the caller, and is released here. A call to
|
|
* queue_me() is typically paired with exactly one call to unqueue_me(). The
|
|
* exceptions involve the PI related operations, which may use unqueue_me_pi()
|
|
* or nothing if the unqueue is done as part of the wake process and the unqueue
|
|
* state is implicit in the state of woken task (see futex_wait_requeue_pi() for
|
|
* an example).
|
|
*/
|
|
static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
|
|
__releases(&hb->lock)
|
|
{
|
|
int prio;
|
|
|
|
/*
|
|
* The priority used to register this element is
|
|
* - either the real thread-priority for the real-time threads
|
|
* (i.e. threads with a priority lower than MAX_RT_PRIO)
|
|
* - or MAX_RT_PRIO for non-RT threads.
|
|
* Thus, all RT-threads are woken first in priority order, and
|
|
* the others are woken last, in FIFO order.
|
|
*/
|
|
prio = min(current->normal_prio, MAX_RT_PRIO);
|
|
|
|
plist_node_init(&q->list, prio);
|
|
plist_add(&q->list, &hb->chain);
|
|
q->task = current;
|
|
spin_unlock(&hb->lock);
|
|
}
|
|
|
|
/**
|
|
* unqueue_me() - Remove the futex_q from its futex_hash_bucket
|
|
* @q: The futex_q to unqueue
|
|
*
|
|
* The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
|
|
* be paired with exactly one earlier call to queue_me().
|
|
*
|
|
* Return:
|
|
* 1 - if the futex_q was still queued (and we removed unqueued it);
|
|
* 0 - if the futex_q was already removed by the waking thread
|
|
*/
|
|
static int unqueue_me(struct futex_q *q)
|
|
{
|
|
spinlock_t *lock_ptr;
|
|
int ret = 0;
|
|
|
|
/* In the common case we don't take the spinlock, which is nice. */
|
|
retry:
|
|
/*
|
|
* q->lock_ptr can change between this read and the following spin_lock.
|
|
* Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
|
|
* optimizing lock_ptr out of the logic below.
|
|
*/
|
|
lock_ptr = READ_ONCE(q->lock_ptr);
|
|
if (lock_ptr != NULL) {
|
|
spin_lock(lock_ptr);
|
|
/*
|
|
* q->lock_ptr can change between reading it and
|
|
* spin_lock(), causing us to take the wrong lock. This
|
|
* corrects the race condition.
|
|
*
|
|
* Reasoning goes like this: if we have the wrong lock,
|
|
* q->lock_ptr must have changed (maybe several times)
|
|
* between reading it and the spin_lock(). It can
|
|
* change again after the spin_lock() but only if it was
|
|
* already changed before the spin_lock(). It cannot,
|
|
* however, change back to the original value. Therefore
|
|
* we can detect whether we acquired the correct lock.
|
|
*/
|
|
if (unlikely(lock_ptr != q->lock_ptr)) {
|
|
spin_unlock(lock_ptr);
|
|
goto retry;
|
|
}
|
|
__unqueue_futex(q);
|
|
|
|
BUG_ON(q->pi_state);
|
|
|
|
spin_unlock(lock_ptr);
|
|
ret = 1;
|
|
}
|
|
|
|
drop_futex_key_refs(&q->key);
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* PI futexes can not be requeued and must remove themself from the
|
|
* hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
|
|
* and dropped here.
|
|
*/
|
|
static void unqueue_me_pi(struct futex_q *q)
|
|
__releases(q->lock_ptr)
|
|
{
|
|
__unqueue_futex(q);
|
|
|
|
BUG_ON(!q->pi_state);
|
|
put_pi_state(q->pi_state);
|
|
q->pi_state = NULL;
|
|
|
|
spin_unlock(q->lock_ptr);
|
|
}
|
|
|
|
/*
|
|
* Fixup the pi_state owner with the new owner.
|
|
*
|
|
* Must be called with hash bucket lock held and mm->sem held for non
|
|
* private futexes.
|
|
*/
|
|
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
|
|
struct task_struct *newowner)
|
|
{
|
|
u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
|
|
struct futex_pi_state *pi_state = q->pi_state;
|
|
struct task_struct *oldowner = pi_state->owner;
|
|
u32 uval, uninitialized_var(curval), newval;
|
|
int ret;
|
|
|
|
/* Owner died? */
|
|
if (!pi_state->owner)
|
|
newtid |= FUTEX_OWNER_DIED;
|
|
|
|
/*
|
|
* We are here either because we stole the rtmutex from the
|
|
* previous highest priority waiter or we are the highest priority
|
|
* waiter but failed to get the rtmutex the first time.
|
|
* We have to replace the newowner TID in the user space variable.
|
|
* This must be atomic as we have to preserve the owner died bit here.
|
|
*
|
|
* Note: We write the user space value _before_ changing the pi_state
|
|
* because we can fault here. Imagine swapped out pages or a fork
|
|
* that marked all the anonymous memory readonly for cow.
|
|
*
|
|
* Modifying pi_state _before_ the user space value would
|
|
* leave the pi_state in an inconsistent state when we fault
|
|
* here, because we need to drop the hash bucket lock to
|
|
* handle the fault. This might be observed in the PID check
|
|
* in lookup_pi_state.
|
|
*/
|
|
retry:
|
|
if (get_futex_value_locked(&uval, uaddr))
|
|
goto handle_fault;
|
|
|
|
while (1) {
|
|
newval = (uval & FUTEX_OWNER_DIED) | newtid;
|
|
|
|
if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
|
|
goto handle_fault;
|
|
if (curval == uval)
|
|
break;
|
|
uval = curval;
|
|
}
|
|
|
|
/*
|
|
* We fixed up user space. Now we need to fix the pi_state
|
|
* itself.
|
|
*/
|
|
if (pi_state->owner != NULL) {
|
|
raw_spin_lock_irq(&pi_state->owner->pi_lock);
|
|
WARN_ON(list_empty(&pi_state->list));
|
|
list_del_init(&pi_state->list);
|
|
raw_spin_unlock_irq(&pi_state->owner->pi_lock);
|
|
}
|
|
|
|
pi_state->owner = newowner;
|
|
|
|
raw_spin_lock_irq(&newowner->pi_lock);
|
|
WARN_ON(!list_empty(&pi_state->list));
|
|
list_add(&pi_state->list, &newowner->pi_state_list);
|
|
raw_spin_unlock_irq(&newowner->pi_lock);
|
|
return 0;
|
|
|
|
/*
|
|
* To handle the page fault we need to drop the hash bucket
|
|
* lock here. That gives the other task (either the highest priority
|
|
* waiter itself or the task which stole the rtmutex) the
|
|
* chance to try the fixup of the pi_state. So once we are
|
|
* back from handling the fault we need to check the pi_state
|
|
* after reacquiring the hash bucket lock and before trying to
|
|
* do another fixup. When the fixup has been done already we
|
|
* simply return.
|
|
*/
|
|
handle_fault:
|
|
spin_unlock(q->lock_ptr);
|
|
|
|
ret = fault_in_user_writeable(uaddr);
|
|
|
|
spin_lock(q->lock_ptr);
|
|
|
|
/*
|
|
* Check if someone else fixed it for us:
|
|
*/
|
|
if (pi_state->owner != oldowner)
|
|
return 0;
|
|
|
|
if (ret)
|
|
return ret;
|
|
|
|
goto retry;
|
|
}
|
|
|
|
static long futex_wait_restart(struct restart_block *restart);
|
|
|
|
/**
|
|
* fixup_owner() - Post lock pi_state and corner case management
|
|
* @uaddr: user address of the futex
|
|
* @q: futex_q (contains pi_state and access to the rt_mutex)
|
|
* @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
|
|
*
|
|
* After attempting to lock an rt_mutex, this function is called to cleanup
|
|
* the pi_state owner as well as handle race conditions that may allow us to
|
|
* acquire the lock. Must be called with the hb lock held.
|
|
*
|
|
* Return:
|
|
* 1 - success, lock taken;
|
|
* 0 - success, lock not taken;
|
|
* <0 - on error (-EFAULT)
|
|
*/
|
|
static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
|
|
{
|
|
struct task_struct *owner;
|
|
int ret = 0;
|
|
|
|
if (locked) {
|
|
/*
|
|
* Got the lock. We might not be the anticipated owner if we
|
|
* did a lock-steal - fix up the PI-state in that case:
|
|
*/
|
|
if (q->pi_state->owner != current)
|
|
ret = fixup_pi_state_owner(uaddr, q, current);
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* Catch the rare case, where the lock was released when we were on the
|
|
* way back before we locked the hash bucket.
|
|
*/
|
|
if (q->pi_state->owner == current) {
|
|
/*
|
|
* Try to get the rt_mutex now. This might fail as some other
|
|
* task acquired the rt_mutex after we removed ourself from the
|
|
* rt_mutex waiters list.
|
|
*/
|
|
if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
|
|
locked = 1;
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* pi_state is incorrect, some other task did a lock steal and
|
|
* we returned due to timeout or signal without taking the
|
|
* rt_mutex. Too late.
|
|
*/
|
|
raw_spin_lock_irq(&q->pi_state->pi_mutex.wait_lock);
|
|
owner = rt_mutex_owner(&q->pi_state->pi_mutex);
|
|
if (!owner)
|
|
owner = rt_mutex_next_owner(&q->pi_state->pi_mutex);
|
|
raw_spin_unlock_irq(&q->pi_state->pi_mutex.wait_lock);
|
|
ret = fixup_pi_state_owner(uaddr, q, owner);
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* Paranoia check. If we did not take the lock, then we should not be
|
|
* the owner of the rt_mutex.
|
|
*/
|
|
if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
|
|
printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
|
|
"pi-state %p\n", ret,
|
|
q->pi_state->pi_mutex.owner,
|
|
q->pi_state->owner);
|
|
|
|
out:
|
|
return ret ? ret : locked;
|
|
}
|
|
|
|
/**
|
|
* futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
|
|
* @hb: the futex hash bucket, must be locked by the caller
|
|
* @q: the futex_q to queue up on
|
|
* @timeout: the prepared hrtimer_sleeper, or null for no timeout
|
|
*/
|
|
static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
|
|
struct hrtimer_sleeper *timeout)
|
|
{
|
|
/*
|
|
* The task state is guaranteed to be set before another task can
|
|
* wake it. set_current_state() is implemented using smp_store_mb() and
|
|
* queue_me() calls spin_unlock() upon completion, both serializing
|
|
* access to the hash list and forcing another memory barrier.
|
|
*/
|
|
set_current_state(TASK_INTERRUPTIBLE);
|
|
queue_me(q, hb);
|
|
|
|
/* Arm the timer */
|
|
if (timeout)
|
|
hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
|
|
|
|
/*
|
|
* If we have been removed from the hash list, then another task
|
|
* has tried to wake us, and we can skip the call to schedule().
|
|
*/
|
|
if (likely(!plist_node_empty(&q->list))) {
|
|
/*
|
|
* If the timer has already expired, current will already be
|
|
* flagged for rescheduling. Only call schedule if there
|
|
* is no timeout, or if it has yet to expire.
|
|
*/
|
|
if (!timeout || timeout->task)
|
|
freezable_schedule();
|
|
}
|
|
__set_current_state(TASK_RUNNING);
|
|
}
|
|
|
|
/**
|
|
* futex_wait_setup() - Prepare to wait on a futex
|
|
* @uaddr: the futex userspace address
|
|
* @val: the expected value
|
|
* @flags: futex flags (FLAGS_SHARED, etc.)
|
|
* @q: the associated futex_q
|
|
* @hb: storage for hash_bucket pointer to be returned to caller
|
|
*
|
|
* Setup the futex_q and locate the hash_bucket. Get the futex value and
|
|
* compare it with the expected value. Handle atomic faults internally.
|
|
* Return with the hb lock held and a q.key reference on success, and unlocked
|
|
* with no q.key reference on failure.
|
|
*
|
|
* Return:
|
|
* 0 - uaddr contains val and hb has been locked;
|
|
* <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
|
|
*/
|
|
static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
|
|
struct futex_q *q, struct futex_hash_bucket **hb)
|
|
{
|
|
u32 uval;
|
|
int ret;
|
|
|
|
/*
|
|
* Access the page AFTER the hash-bucket is locked.
|
|
* Order is important:
|
|
*
|
|
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
|
|
* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
|
|
*
|
|
* The basic logical guarantee of a futex is that it blocks ONLY
|
|
* if cond(var) is known to be true at the time of blocking, for
|
|
* any cond. If we locked the hash-bucket after testing *uaddr, that
|
|
* would open a race condition where we could block indefinitely with
|
|
* cond(var) false, which would violate the guarantee.
|
|
*
|
|
* On the other hand, we insert q and release the hash-bucket only
|
|
* after testing *uaddr. This guarantees that futex_wait() will NOT
|
|
* absorb a wakeup if *uaddr does not match the desired values
|
|
* while the syscall executes.
|
|
*/
|
|
retry:
|
|
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
return ret;
|
|
|
|
retry_private:
|
|
*hb = queue_lock(q);
|
|
|
|
ret = get_futex_value_locked(&uval, uaddr);
|
|
|
|
if (ret) {
|
|
queue_unlock(*hb);
|
|
|
|
ret = get_user(uval, uaddr);
|
|
if (ret)
|
|
goto out;
|
|
|
|
if (!(flags & FLAGS_SHARED))
|
|
goto retry_private;
|
|
|
|
put_futex_key(&q->key);
|
|
goto retry;
|
|
}
|
|
|
|
if (uval != val) {
|
|
queue_unlock(*hb);
|
|
ret = -EWOULDBLOCK;
|
|
}
|
|
|
|
out:
|
|
if (ret)
|
|
put_futex_key(&q->key);
|
|
return ret;
|
|
}
|
|
|
|
static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
|
|
ktime_t *abs_time, u32 bitset)
|
|
{
|
|
struct hrtimer_sleeper timeout, *to = NULL;
|
|
struct restart_block *restart;
|
|
struct futex_hash_bucket *hb;
|
|
struct futex_q q = futex_q_init;
|
|
int ret;
|
|
|
|
if (!bitset)
|
|
return -EINVAL;
|
|
q.bitset = bitset;
|
|
|
|
if (abs_time) {
|
|
to = &timeout;
|
|
|
|
hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
|
|
CLOCK_REALTIME : CLOCK_MONOTONIC,
|
|
HRTIMER_MODE_ABS);
|
|
hrtimer_init_sleeper(to, current);
|
|
hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
|
current->timer_slack_ns);
|
|
}
|
|
|
|
retry:
|
|
/*
|
|
* Prepare to wait on uaddr. On success, holds hb lock and increments
|
|
* q.key refs.
|
|
*/
|
|
ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
|
if (ret)
|
|
goto out;
|
|
|
|
/* queue_me and wait for wakeup, timeout, or a signal. */
|
|
futex_wait_queue_me(hb, &q, to);
|
|
|
|
/* If we were woken (and unqueued), we succeeded, whatever. */
|
|
ret = 0;
|
|
/* unqueue_me() drops q.key ref */
|
|
if (!unqueue_me(&q))
|
|
goto out;
|
|
ret = -ETIMEDOUT;
|
|
if (to && !to->task)
|
|
goto out;
|
|
|
|
/*
|
|
* We expect signal_pending(current), but we might be the
|
|
* victim of a spurious wakeup as well.
|
|
*/
|
|
if (!signal_pending(current))
|
|
goto retry;
|
|
|
|
ret = -ERESTARTSYS;
|
|
if (!abs_time)
|
|
goto out;
|
|
|
|
restart = ¤t->restart_block;
|
|
restart->fn = futex_wait_restart;
|
|
restart->futex.uaddr = uaddr;
|
|
restart->futex.val = val;
|
|
restart->futex.time = abs_time->tv64;
|
|
restart->futex.bitset = bitset;
|
|
restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
|
|
|
|
ret = -ERESTART_RESTARTBLOCK;
|
|
|
|
out:
|
|
if (to) {
|
|
hrtimer_cancel(&to->timer);
|
|
destroy_hrtimer_on_stack(&to->timer);
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
|
|
static long futex_wait_restart(struct restart_block *restart)
|
|
{
|
|
u32 __user *uaddr = restart->futex.uaddr;
|
|
ktime_t t, *tp = NULL;
|
|
|
|
if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
|
|
t.tv64 = restart->futex.time;
|
|
tp = &t;
|
|
}
|
|
restart->fn = do_no_restart_syscall;
|
|
|
|
return (long)futex_wait(uaddr, restart->futex.flags,
|
|
restart->futex.val, tp, restart->futex.bitset);
|
|
}
|
|
|
|
|
|
/*
|
|
* Userspace tried a 0 -> TID atomic transition of the futex value
|
|
* and failed. The kernel side here does the whole locking operation:
|
|
* if there are waiters then it will block as a consequence of relying
|
|
* on rt-mutexes, it does PI, etc. (Due to races the kernel might see
|
|
* a 0 value of the futex too.).
|
|
*
|
|
* Also serves as futex trylock_pi()'ing, and due semantics.
|
|
*/
|
|
static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
|
|
ktime_t *time, int trylock)
|
|
{
|
|
struct hrtimer_sleeper timeout, *to = NULL;
|
|
struct futex_hash_bucket *hb;
|
|
struct futex_q q = futex_q_init;
|
|
int res, ret;
|
|
|
|
if (refill_pi_state_cache())
|
|
return -ENOMEM;
|
|
|
|
if (time) {
|
|
to = &timeout;
|
|
hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
|
|
HRTIMER_MODE_ABS);
|
|
hrtimer_init_sleeper(to, current);
|
|
hrtimer_set_expires(&to->timer, *time);
|
|
}
|
|
|
|
retry:
|
|
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
retry_private:
|
|
hb = queue_lock(&q);
|
|
|
|
ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
|
|
if (unlikely(ret)) {
|
|
/*
|
|
* Atomic work succeeded and we got the lock,
|
|
* or failed. Either way, we do _not_ block.
|
|
*/
|
|
switch (ret) {
|
|
case 1:
|
|
/* We got the lock. */
|
|
ret = 0;
|
|
goto out_unlock_put_key;
|
|
case -EFAULT:
|
|
goto uaddr_faulted;
|
|
case -EAGAIN:
|
|
/*
|
|
* Two reasons for this:
|
|
* - Task is exiting and we just wait for the
|
|
* exit to complete.
|
|
* - The user space value changed.
|
|
*/
|
|
queue_unlock(hb);
|
|
put_futex_key(&q.key);
|
|
cond_resched();
|
|
goto retry;
|
|
default:
|
|
goto out_unlock_put_key;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Only actually queue now that the atomic ops are done:
|
|
*/
|
|
queue_me(&q, hb);
|
|
|
|
WARN_ON(!q.pi_state);
|
|
/*
|
|
* Block on the PI mutex:
|
|
*/
|
|
if (!trylock) {
|
|
ret = rt_mutex_timed_futex_lock(&q.pi_state->pi_mutex, to);
|
|
} else {
|
|
ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
|
|
/* Fixup the trylock return value: */
|
|
ret = ret ? 0 : -EWOULDBLOCK;
|
|
}
|
|
|
|
spin_lock(q.lock_ptr);
|
|
/*
|
|
* Fixup the pi_state owner and possibly acquire the lock if we
|
|
* haven't already.
|
|
*/
|
|
res = fixup_owner(uaddr, &q, !ret);
|
|
/*
|
|
* If fixup_owner() returned an error, proprogate that. If it acquired
|
|
* the lock, clear our -ETIMEDOUT or -EINTR.
|
|
*/
|
|
if (res)
|
|
ret = (res < 0) ? res : 0;
|
|
|
|
/*
|
|
* If fixup_owner() faulted and was unable to handle the fault, unlock
|
|
* it and return the fault to userspace.
|
|
*/
|
|
if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
|
|
rt_mutex_unlock(&q.pi_state->pi_mutex);
|
|
|
|
/* Unqueue and drop the lock */
|
|
unqueue_me_pi(&q);
|
|
|
|
goto out_put_key;
|
|
|
|
out_unlock_put_key:
|
|
queue_unlock(hb);
|
|
|
|
out_put_key:
|
|
put_futex_key(&q.key);
|
|
out:
|
|
if (to)
|
|
destroy_hrtimer_on_stack(&to->timer);
|
|
return ret != -EINTR ? ret : -ERESTARTNOINTR;
|
|
|
|
uaddr_faulted:
|
|
queue_unlock(hb);
|
|
|
|
ret = fault_in_user_writeable(uaddr);
|
|
if (ret)
|
|
goto out_put_key;
|
|
|
|
if (!(flags & FLAGS_SHARED))
|
|
goto retry_private;
|
|
|
|
put_futex_key(&q.key);
|
|
goto retry;
|
|
}
|
|
|
|
/*
|
|
* Userspace attempted a TID -> 0 atomic transition, and failed.
|
|
* This is the in-kernel slowpath: we look up the PI state (if any),
|
|
* and do the rt-mutex unlock.
|
|
*/
|
|
static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
|
|
{
|
|
u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
|
|
union futex_key key = FUTEX_KEY_INIT;
|
|
struct futex_hash_bucket *hb;
|
|
struct futex_q *match;
|
|
int ret;
|
|
|
|
retry:
|
|
if (get_user(uval, uaddr))
|
|
return -EFAULT;
|
|
/*
|
|
* We release only a lock we actually own:
|
|
*/
|
|
if ((uval & FUTEX_TID_MASK) != vpid)
|
|
return -EPERM;
|
|
|
|
ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
|
|
if (ret)
|
|
return ret;
|
|
|
|
hb = hash_futex(&key);
|
|
spin_lock(&hb->lock);
|
|
|
|
/*
|
|
* Check waiters first. We do not trust user space values at
|
|
* all and we at least want to know if user space fiddled
|
|
* with the futex value instead of blindly unlocking.
|
|
*/
|
|
match = futex_top_waiter(hb, &key);
|
|
if (match) {
|
|
ret = wake_futex_pi(uaddr, uval, match, hb);
|
|
/*
|
|
* In case of success wake_futex_pi dropped the hash
|
|
* bucket lock.
|
|
*/
|
|
if (!ret)
|
|
goto out_putkey;
|
|
/*
|
|
* The atomic access to the futex value generated a
|
|
* pagefault, so retry the user-access and the wakeup:
|
|
*/
|
|
if (ret == -EFAULT)
|
|
goto pi_faulted;
|
|
/*
|
|
* A unconditional UNLOCK_PI op raced against a waiter
|
|
* setting the FUTEX_WAITERS bit. Try again.
|
|
*/
|
|
if (ret == -EAGAIN) {
|
|
spin_unlock(&hb->lock);
|
|
put_futex_key(&key);
|
|
goto retry;
|
|
}
|
|
/*
|
|
* wake_futex_pi has detected invalid state. Tell user
|
|
* space.
|
|
*/
|
|
goto out_unlock;
|
|
}
|
|
|
|
/*
|
|
* We have no kernel internal state, i.e. no waiters in the
|
|
* kernel. Waiters which are about to queue themselves are stuck
|
|
* on hb->lock. So we can safely ignore them. We do neither
|
|
* preserve the WAITERS bit not the OWNER_DIED one. We are the
|
|
* owner.
|
|
*/
|
|
if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
|
|
goto pi_faulted;
|
|
|
|
/*
|
|
* If uval has changed, let user space handle it.
|
|
*/
|
|
ret = (curval == uval) ? 0 : -EAGAIN;
|
|
|
|
out_unlock:
|
|
spin_unlock(&hb->lock);
|
|
out_putkey:
|
|
put_futex_key(&key);
|
|
return ret;
|
|
|
|
pi_faulted:
|
|
spin_unlock(&hb->lock);
|
|
put_futex_key(&key);
|
|
|
|
ret = fault_in_user_writeable(uaddr);
|
|
if (!ret)
|
|
goto retry;
|
|
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
|
|
* @hb: the hash_bucket futex_q was original enqueued on
|
|
* @q: the futex_q woken while waiting to be requeued
|
|
* @key2: the futex_key of the requeue target futex
|
|
* @timeout: the timeout associated with the wait (NULL if none)
|
|
*
|
|
* Detect if the task was woken on the initial futex as opposed to the requeue
|
|
* target futex. If so, determine if it was a timeout or a signal that caused
|
|
* the wakeup and return the appropriate error code to the caller. Must be
|
|
* called with the hb lock held.
|
|
*
|
|
* Return:
|
|
* 0 = no early wakeup detected;
|
|
* <0 = -ETIMEDOUT or -ERESTARTNOINTR
|
|
*/
|
|
static inline
|
|
int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
|
|
struct futex_q *q, union futex_key *key2,
|
|
struct hrtimer_sleeper *timeout)
|
|
{
|
|
int ret = 0;
|
|
|
|
/*
|
|
* With the hb lock held, we avoid races while we process the wakeup.
|
|
* We only need to hold hb (and not hb2) to ensure atomicity as the
|
|
* wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
|
|
* It can't be requeued from uaddr2 to something else since we don't
|
|
* support a PI aware source futex for requeue.
|
|
*/
|
|
if (!match_futex(&q->key, key2)) {
|
|
WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
|
|
/*
|
|
* We were woken prior to requeue by a timeout or a signal.
|
|
* Unqueue the futex_q and determine which it was.
|
|
*/
|
|
plist_del(&q->list, &hb->chain);
|
|
hb_waiters_dec(hb);
|
|
|
|
/* Handle spurious wakeups gracefully */
|
|
ret = -EWOULDBLOCK;
|
|
if (timeout && !timeout->task)
|
|
ret = -ETIMEDOUT;
|
|
else if (signal_pending(current))
|
|
ret = -ERESTARTNOINTR;
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
|
|
* @uaddr: the futex we initially wait on (non-pi)
|
|
* @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
|
|
* the same type, no requeueing from private to shared, etc.
|
|
* @val: the expected value of uaddr
|
|
* @abs_time: absolute timeout
|
|
* @bitset: 32 bit wakeup bitset set by userspace, defaults to all
|
|
* @uaddr2: the pi futex we will take prior to returning to user-space
|
|
*
|
|
* The caller will wait on uaddr and will be requeued by futex_requeue() to
|
|
* uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
|
|
* on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
|
|
* userspace. This ensures the rt_mutex maintains an owner when it has waiters;
|
|
* without one, the pi logic would not know which task to boost/deboost, if
|
|
* there was a need to.
|
|
*
|
|
* We call schedule in futex_wait_queue_me() when we enqueue and return there
|
|
* via the following--
|
|
* 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
|
|
* 2) wakeup on uaddr2 after a requeue
|
|
* 3) signal
|
|
* 4) timeout
|
|
*
|
|
* If 3, cleanup and return -ERESTARTNOINTR.
|
|
*
|
|
* If 2, we may then block on trying to take the rt_mutex and return via:
|
|
* 5) successful lock
|
|
* 6) signal
|
|
* 7) timeout
|
|
* 8) other lock acquisition failure
|
|
*
|
|
* If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
|
|
*
|
|
* If 4 or 7, we cleanup and return with -ETIMEDOUT.
|
|
*
|
|
* Return:
|
|
* 0 - On success;
|
|
* <0 - On error
|
|
*/
|
|
static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
|
|
u32 val, ktime_t *abs_time, u32 bitset,
|
|
u32 __user *uaddr2)
|
|
{
|
|
struct hrtimer_sleeper timeout, *to = NULL;
|
|
struct rt_mutex_waiter rt_waiter;
|
|
struct rt_mutex *pi_mutex = NULL;
|
|
struct futex_hash_bucket *hb;
|
|
union futex_key key2 = FUTEX_KEY_INIT;
|
|
struct futex_q q = futex_q_init;
|
|
int res, ret;
|
|
|
|
if (uaddr == uaddr2)
|
|
return -EINVAL;
|
|
|
|
if (!bitset)
|
|
return -EINVAL;
|
|
|
|
if (abs_time) {
|
|
to = &timeout;
|
|
hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
|
|
CLOCK_REALTIME : CLOCK_MONOTONIC,
|
|
HRTIMER_MODE_ABS);
|
|
hrtimer_init_sleeper(to, current);
|
|
hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
|
current->timer_slack_ns);
|
|
}
|
|
|
|
/*
|
|
* The waiter is allocated on our stack, manipulated by the requeue
|
|
* code while we sleep on uaddr.
|
|
*/
|
|
debug_rt_mutex_init_waiter(&rt_waiter);
|
|
RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
|
|
RB_CLEAR_NODE(&rt_waiter.tree_entry);
|
|
rt_waiter.task = NULL;
|
|
|
|
ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
q.bitset = bitset;
|
|
q.rt_waiter = &rt_waiter;
|
|
q.requeue_pi_key = &key2;
|
|
|
|
/*
|
|
* Prepare to wait on uaddr. On success, increments q.key (key1) ref
|
|
* count.
|
|
*/
|
|
ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
|
|
if (ret)
|
|
goto out_key2;
|
|
|
|
/*
|
|
* The check above which compares uaddrs is not sufficient for
|
|
* shared futexes. We need to compare the keys:
|
|
*/
|
|
if (match_futex(&q.key, &key2)) {
|
|
queue_unlock(hb);
|
|
ret = -EINVAL;
|
|
goto out_put_keys;
|
|
}
|
|
|
|
/* Queue the futex_q, drop the hb lock, wait for wakeup. */
|
|
futex_wait_queue_me(hb, &q, to);
|
|
|
|
spin_lock(&hb->lock);
|
|
ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
|
|
spin_unlock(&hb->lock);
|
|
if (ret)
|
|
goto out_put_keys;
|
|
|
|
/*
|
|
* In order for us to be here, we know our q.key == key2, and since
|
|
* we took the hb->lock above, we also know that futex_requeue() has
|
|
* completed and we no longer have to concern ourselves with a wakeup
|
|
* race with the atomic proxy lock acquisition by the requeue code. The
|
|
* futex_requeue dropped our key1 reference and incremented our key2
|
|
* reference count.
|
|
*/
|
|
|
|
/* Check if the requeue code acquired the second futex for us. */
|
|
if (!q.rt_waiter) {
|
|
/*
|
|
* Got the lock. We might not be the anticipated owner if we
|
|
* did a lock-steal - fix up the PI-state in that case.
|
|
*/
|
|
if (q.pi_state && (q.pi_state->owner != current)) {
|
|
spin_lock(q.lock_ptr);
|
|
ret = fixup_pi_state_owner(uaddr2, &q, current);
|
|
/*
|
|
* Drop the reference to the pi state which
|
|
* the requeue_pi() code acquired for us.
|
|
*/
|
|
put_pi_state(q.pi_state);
|
|
spin_unlock(q.lock_ptr);
|
|
}
|
|
} else {
|
|
/*
|
|
* We have been woken up by futex_unlock_pi(), a timeout, or a
|
|
* signal. futex_unlock_pi() will not destroy the lock_ptr nor
|
|
* the pi_state.
|
|
*/
|
|
WARN_ON(!q.pi_state);
|
|
pi_mutex = &q.pi_state->pi_mutex;
|
|
ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter);
|
|
debug_rt_mutex_free_waiter(&rt_waiter);
|
|
|
|
spin_lock(q.lock_ptr);
|
|
/*
|
|
* Fixup the pi_state owner and possibly acquire the lock if we
|
|
* haven't already.
|
|
*/
|
|
res = fixup_owner(uaddr2, &q, !ret);
|
|
/*
|
|
* If fixup_owner() returned an error, proprogate that. If it
|
|
* acquired the lock, clear -ETIMEDOUT or -EINTR.
|
|
*/
|
|
if (res)
|
|
ret = (res < 0) ? res : 0;
|
|
|
|
/* Unqueue and drop the lock. */
|
|
unqueue_me_pi(&q);
|
|
}
|
|
|
|
/*
|
|
* If fixup_pi_state_owner() faulted and was unable to handle the
|
|
* fault, unlock the rt_mutex and return the fault to userspace.
|
|
*/
|
|
if (ret == -EFAULT) {
|
|
if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
|
|
rt_mutex_unlock(pi_mutex);
|
|
} else if (ret == -EINTR) {
|
|
/*
|
|
* We've already been requeued, but cannot restart by calling
|
|
* futex_lock_pi() directly. We could restart this syscall, but
|
|
* it would detect that the user space "val" changed and return
|
|
* -EWOULDBLOCK. Save the overhead of the restart and return
|
|
* -EWOULDBLOCK directly.
|
|
*/
|
|
ret = -EWOULDBLOCK;
|
|
}
|
|
|
|
out_put_keys:
|
|
put_futex_key(&q.key);
|
|
out_key2:
|
|
put_futex_key(&key2);
|
|
|
|
out:
|
|
if (to) {
|
|
hrtimer_cancel(&to->timer);
|
|
destroy_hrtimer_on_stack(&to->timer);
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Support for robust futexes: the kernel cleans up held futexes at
|
|
* thread exit time.
|
|
*
|
|
* Implementation: user-space maintains a per-thread list of locks it
|
|
* is holding. Upon do_exit(), the kernel carefully walks this list,
|
|
* and marks all locks that are owned by this thread with the
|
|
* FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
|
|
* always manipulated with the lock held, so the list is private and
|
|
* per-thread. Userspace also maintains a per-thread 'list_op_pending'
|
|
* field, to allow the kernel to clean up if the thread dies after
|
|
* acquiring the lock, but just before it could have added itself to
|
|
* the list. There can only be one such pending lock.
|
|
*/
|
|
|
|
/**
|
|
* sys_set_robust_list() - Set the robust-futex list head of a task
|
|
* @head: pointer to the list-head
|
|
* @len: length of the list-head, as userspace expects
|
|
*/
|
|
SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
|
|
size_t, len)
|
|
{
|
|
if (!futex_cmpxchg_enabled)
|
|
return -ENOSYS;
|
|
/*
|
|
* The kernel knows only one size for now:
|
|
*/
|
|
if (unlikely(len != sizeof(*head)))
|
|
return -EINVAL;
|
|
|
|
current->robust_list = head;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* sys_get_robust_list() - Get the robust-futex list head of a task
|
|
* @pid: pid of the process [zero for current task]
|
|
* @head_ptr: pointer to a list-head pointer, the kernel fills it in
|
|
* @len_ptr: pointer to a length field, the kernel fills in the header size
|
|
*/
|
|
SYSCALL_DEFINE3(get_robust_list, int, pid,
|
|
struct robust_list_head __user * __user *, head_ptr,
|
|
size_t __user *, len_ptr)
|
|
{
|
|
struct robust_list_head __user *head;
|
|
unsigned long ret;
|
|
struct task_struct *p;
|
|
|
|
if (!futex_cmpxchg_enabled)
|
|
return -ENOSYS;
|
|
|
|
rcu_read_lock();
|
|
|
|
ret = -ESRCH;
|
|
if (!pid)
|
|
p = current;
|
|
else {
|
|
p = find_task_by_vpid(pid);
|
|
if (!p)
|
|
goto err_unlock;
|
|
}
|
|
|
|
ret = -EPERM;
|
|
if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
|
|
goto err_unlock;
|
|
|
|
head = p->robust_list;
|
|
rcu_read_unlock();
|
|
|
|
if (put_user(sizeof(*head), len_ptr))
|
|
return -EFAULT;
|
|
return put_user(head, head_ptr);
|
|
|
|
err_unlock:
|
|
rcu_read_unlock();
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Process a futex-list entry, check whether it's owned by the
|
|
* dying task, and do notification if so:
|
|
*/
|
|
int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
|
|
{
|
|
u32 uval, uninitialized_var(nval), mval;
|
|
|
|
retry:
|
|
if (get_user(uval, uaddr))
|
|
return -1;
|
|
|
|
if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
|
|
/*
|
|
* Ok, this dying thread is truly holding a futex
|
|
* of interest. Set the OWNER_DIED bit atomically
|
|
* via cmpxchg, and if the value had FUTEX_WAITERS
|
|
* set, wake up a waiter (if any). (We have to do a
|
|
* futex_wake() even if OWNER_DIED is already set -
|
|
* to handle the rare but possible case of recursive
|
|
* thread-death.) The rest of the cleanup is done in
|
|
* userspace.
|
|
*/
|
|
mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
|
|
/*
|
|
* We are not holding a lock here, but we want to have
|
|
* the pagefault_disable/enable() protection because
|
|
* we want to handle the fault gracefully. If the
|
|
* access fails we try to fault in the futex with R/W
|
|
* verification via get_user_pages. get_user() above
|
|
* does not guarantee R/W access. If that fails we
|
|
* give up and leave the futex locked.
|
|
*/
|
|
if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
|
|
if (fault_in_user_writeable(uaddr))
|
|
return -1;
|
|
goto retry;
|
|
}
|
|
if (nval != uval)
|
|
goto retry;
|
|
|
|
/*
|
|
* Wake robust non-PI futexes here. The wakeup of
|
|
* PI futexes happens in exit_pi_state():
|
|
*/
|
|
if (!pi && (uval & FUTEX_WAITERS))
|
|
futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Fetch a robust-list pointer. Bit 0 signals PI futexes:
|
|
*/
|
|
static inline int fetch_robust_entry(struct robust_list __user **entry,
|
|
struct robust_list __user * __user *head,
|
|
unsigned int *pi)
|
|
{
|
|
unsigned long uentry;
|
|
|
|
if (get_user(uentry, (unsigned long __user *)head))
|
|
return -EFAULT;
|
|
|
|
*entry = (void __user *)(uentry & ~1UL);
|
|
*pi = uentry & 1;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Walk curr->robust_list (very carefully, it's a userspace list!)
|
|
* and mark any locks found there dead, and notify any waiters.
|
|
*
|
|
* We silently return on any sign of list-walking problem.
|
|
*/
|
|
void exit_robust_list(struct task_struct *curr)
|
|
{
|
|
struct robust_list_head __user *head = curr->robust_list;
|
|
struct robust_list __user *entry, *next_entry, *pending;
|
|
unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
|
|
unsigned int uninitialized_var(next_pi);
|
|
unsigned long futex_offset;
|
|
int rc;
|
|
|
|
if (!futex_cmpxchg_enabled)
|
|
return;
|
|
|
|
/*
|
|
* Fetch the list head (which was registered earlier, via
|
|
* sys_set_robust_list()):
|
|
*/
|
|
if (fetch_robust_entry(&entry, &head->list.next, &pi))
|
|
return;
|
|
/*
|
|
* Fetch the relative futex offset:
|
|
*/
|
|
if (get_user(futex_offset, &head->futex_offset))
|
|
return;
|
|
/*
|
|
* Fetch any possibly pending lock-add first, and handle it
|
|
* if it exists:
|
|
*/
|
|
if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
|
|
return;
|
|
|
|
next_entry = NULL; /* avoid warning with gcc */
|
|
while (entry != &head->list) {
|
|
/*
|
|
* Fetch the next entry in the list before calling
|
|
* handle_futex_death:
|
|
*/
|
|
rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
|
|
/*
|
|
* A pending lock might already be on the list, so
|
|
* don't process it twice:
|
|
*/
|
|
if (entry != pending)
|
|
if (handle_futex_death((void __user *)entry + futex_offset,
|
|
curr, pi))
|
|
return;
|
|
if (rc)
|
|
return;
|
|
entry = next_entry;
|
|
pi = next_pi;
|
|
/*
|
|
* Avoid excessively long or circular lists:
|
|
*/
|
|
if (!--limit)
|
|
break;
|
|
|
|
cond_resched();
|
|
}
|
|
|
|
if (pending)
|
|
handle_futex_death((void __user *)pending + futex_offset,
|
|
curr, pip);
|
|
}
|
|
|
|
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
|
|
u32 __user *uaddr2, u32 val2, u32 val3)
|
|
{
|
|
int cmd = op & FUTEX_CMD_MASK;
|
|
unsigned int flags = 0;
|
|
|
|
if (!(op & FUTEX_PRIVATE_FLAG))
|
|
flags |= FLAGS_SHARED;
|
|
|
|
if (op & FUTEX_CLOCK_REALTIME) {
|
|
flags |= FLAGS_CLOCKRT;
|
|
if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
|
|
cmd != FUTEX_WAIT_REQUEUE_PI)
|
|
return -ENOSYS;
|
|
}
|
|
|
|
switch (cmd) {
|
|
case FUTEX_LOCK_PI:
|
|
case FUTEX_UNLOCK_PI:
|
|
case FUTEX_TRYLOCK_PI:
|
|
case FUTEX_WAIT_REQUEUE_PI:
|
|
case FUTEX_CMP_REQUEUE_PI:
|
|
if (!futex_cmpxchg_enabled)
|
|
return -ENOSYS;
|
|
}
|
|
|
|
switch (cmd) {
|
|
case FUTEX_WAIT:
|
|
val3 = FUTEX_BITSET_MATCH_ANY;
|
|
case FUTEX_WAIT_BITSET:
|
|
return futex_wait(uaddr, flags, val, timeout, val3);
|
|
case FUTEX_WAKE:
|
|
val3 = FUTEX_BITSET_MATCH_ANY;
|
|
case FUTEX_WAKE_BITSET:
|
|
return futex_wake(uaddr, flags, val, val3);
|
|
case FUTEX_REQUEUE:
|
|
return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
|
|
case FUTEX_CMP_REQUEUE:
|
|
return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
|
|
case FUTEX_WAKE_OP:
|
|
return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
|
|
case FUTEX_LOCK_PI:
|
|
return futex_lock_pi(uaddr, flags, timeout, 0);
|
|
case FUTEX_UNLOCK_PI:
|
|
return futex_unlock_pi(uaddr, flags);
|
|
case FUTEX_TRYLOCK_PI:
|
|
return futex_lock_pi(uaddr, flags, NULL, 1);
|
|
case FUTEX_WAIT_REQUEUE_PI:
|
|
val3 = FUTEX_BITSET_MATCH_ANY;
|
|
return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
|
|
uaddr2);
|
|
case FUTEX_CMP_REQUEUE_PI:
|
|
return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
|
|
}
|
|
return -ENOSYS;
|
|
}
|
|
|
|
|
|
SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
|
|
struct timespec __user *, utime, u32 __user *, uaddr2,
|
|
u32, val3)
|
|
{
|
|
struct timespec ts;
|
|
ktime_t t, *tp = NULL;
|
|
u32 val2 = 0;
|
|
int cmd = op & FUTEX_CMD_MASK;
|
|
|
|
if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
|
|
cmd == FUTEX_WAIT_BITSET ||
|
|
cmd == FUTEX_WAIT_REQUEUE_PI)) {
|
|
if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
|
|
return -EFAULT;
|
|
if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
|
|
return -EFAULT;
|
|
if (!timespec_valid(&ts))
|
|
return -EINVAL;
|
|
|
|
t = timespec_to_ktime(ts);
|
|
if (cmd == FUTEX_WAIT)
|
|
t = ktime_add_safe(ktime_get(), t);
|
|
tp = &t;
|
|
}
|
|
/*
|
|
* requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
|
|
* number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
|
|
*/
|
|
if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
|
|
cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
|
|
val2 = (u32) (unsigned long) utime;
|
|
|
|
return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
|
|
}
|
|
|
|
static void __init futex_detect_cmpxchg(void)
|
|
{
|
|
#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
|
|
u32 curval;
|
|
|
|
/*
|
|
* This will fail and we want it. Some arch implementations do
|
|
* runtime detection of the futex_atomic_cmpxchg_inatomic()
|
|
* functionality. We want to know that before we call in any
|
|
* of the complex code paths. Also we want to prevent
|
|
* registration of robust lists in that case. NULL is
|
|
* guaranteed to fault and we get -EFAULT on functional
|
|
* implementation, the non-functional ones will return
|
|
* -ENOSYS.
|
|
*/
|
|
if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
|
|
futex_cmpxchg_enabled = 1;
|
|
#endif
|
|
}
|
|
|
|
static int __init futex_init(void)
|
|
{
|
|
unsigned int futex_shift;
|
|
unsigned long i;
|
|
|
|
#if CONFIG_BASE_SMALL
|
|
futex_hashsize = 16;
|
|
#else
|
|
futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
|
|
#endif
|
|
|
|
futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
|
|
futex_hashsize, 0,
|
|
futex_hashsize < 256 ? HASH_SMALL : 0,
|
|
&futex_shift, NULL,
|
|
futex_hashsize, futex_hashsize);
|
|
futex_hashsize = 1UL << futex_shift;
|
|
|
|
futex_detect_cmpxchg();
|
|
|
|
for (i = 0; i < futex_hashsize; i++) {
|
|
atomic_set(&futex_queues[i].waiters, 0);
|
|
plist_head_init(&futex_queues[i].chain);
|
|
spin_lock_init(&futex_queues[i].lock);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
__initcall(futex_init);
|