linux/fs/notify/mark.c
Lino Sanfilippo 6960b0d909 fsnotify: change locking order
On Mon, Aug 01, 2011 at 04:38:22PM -0400, Eric Paris wrote:
>
> I finally built and tested a v3.0 kernel with these patches (I know I'm
> SOOOOOO far behind).  Not what I hoped for:
>
> > [  150.937798] VFS: Busy inodes after unmount of tmpfs. Self-destruct in 5 seconds.  Have a nice day...
> > [  150.945290] BUG: unable to handle kernel NULL pointer dereference at 0000000000000070
> > [  150.946012] IP: [<ffffffff810ffd58>] shmem_free_inode+0x18/0x50
> > [  150.946012] PGD 2bf9e067 PUD 2bf9f067 PMD 0
> > [  150.946012] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> > [  150.946012] CPU 0
> > [  150.946012] Modules linked in: nfs lockd fscache auth_rpcgss nfs_acl sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables ext4 jbd2 crc16 joydev ata_piix i2c_piix4 pcspkr uinput ipv6 autofs4 usbhid [last unloaded: scsi_wait_scan]
> > [  150.946012]
> > [  150.946012] Pid: 2764, comm: syscall_thrash Not tainted 3.0.0+ #1 Red Hat KVM
> > [  150.946012] RIP: 0010:[<ffffffff810ffd58>]  [<ffffffff810ffd58>] shmem_free_inode+0x18/0x50
> > [  150.946012] RSP: 0018:ffff88002c2e5df8  EFLAGS: 00010282
> > [  150.946012] RAX: 000000004e370d9f RBX: 0000000000000000 RCX: ffff88003a029438
> > [  150.946012] RDX: 0000000033630a5f RSI: 0000000000000000 RDI: ffff88003491c240
> > [  150.946012] RBP: ffff88002c2e5e08 R08: 0000000000000000 R09: 0000000000000000
> > [  150.946012] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88003a029428
> > [  150.946012] R13: ffff88003a029428 R14: ffff88003a029428 R15: ffff88003499a610
> > [  150.946012] FS:  00007f5a05420700(0000) GS:ffff88003f600000(0000) knlGS:0000000000000000
> > [  150.946012] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > [  150.946012] CR2: 0000000000000070 CR3: 000000002a662000 CR4: 00000000000006f0
> > [  150.946012] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [  150.946012] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> > [  150.946012] Process syscall_thrash (pid: 2764, threadinfo ffff88002c2e4000, task ffff88002bfbc760)
> > [  150.946012] Stack:
> > [  150.946012]  ffff88003a029438 ffff88003a029428 ffff88002c2e5e38 ffffffff81102f76
> > [  150.946012]  ffff88003a029438 ffff88003a029598 ffffffff8160f9c0 ffff88002c221250
> > [  150.946012]  ffff88002c2e5e68 ffffffff8115e9be ffff88002c2e5e68 ffff88003a029438
> > [  150.946012] Call Trace:
> > [  150.946012]  [<ffffffff81102f76>] shmem_evict_inode+0x76/0x130
> > [  150.946012]  [<ffffffff8115e9be>] evict+0x7e/0x170
> > [  150.946012]  [<ffffffff8115ee40>] iput_final+0xd0/0x190
> > [  150.946012]  [<ffffffff8115ef33>] iput+0x33/0x40
> > [  150.946012]  [<ffffffff81180205>] fsnotify_destroy_mark_locked+0x145/0x160
> > [  150.946012]  [<ffffffff81180316>] fsnotify_destroy_mark+0x36/0x50
> > [  150.946012]  [<ffffffff81181937>] sys_inotify_rm_watch+0x77/0xd0
> > [  150.946012]  [<ffffffff815aca52>] system_call_fastpath+0x16/0x1b
> > [  150.946012] Code: 67 4a 00 b8 e4 ff ff ff eb aa 66 0f 1f 84 00 00 00 00 00 55 48 89 e5 48 83 ec 10 48 89 1c 24 4c 89 64 24 08 48 8b 9f 40 05 00 00
> > [  150.946012]  83 7b 70 00 74 1c 4c 8d a3 80 00 00 00 4c 89 e7 e8 d2 5d 4a
> > [  150.946012] RIP  [<ffffffff810ffd58>] shmem_free_inode+0x18/0x50
> > [  150.946012]  RSP <ffff88002c2e5df8>
> > [  150.946012] CR2: 0000000000000070
>
> Looks at aweful lot like the problem from:
> http://www.spinics.net/lists/linux-fsdevel/msg46101.html
>

I tried to reproduce this bug with your test program, but without success.
However, if I understand correctly, this occurs since we dont hold any locks when
we call iput() in mark_destroy(), right?
With the patches you tested, iput() is also not called within any lock, since the
groups mark_mutex is released temporarily before iput() is called.  This is, since
the original codes behaviour is similar.
However since we now have a mutex as the biggest lock, we can do what you
suggested (http://www.spinics.net/lists/linux-fsdevel/msg46107.html) and
call iput() with the mutex held to avoid the race.
The patch below implements this. It uses nested locking to avoid deadlock in case
we do the final iput() on an inode which still holds marks and thus would take
the mutex again when calling fsnotify_inode_delete() in destroy_inode().

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: Eric Paris <eparis@redhat.com>
2012-12-11 13:44:36 -05:00

382 lines
11 KiB
C

/*
* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; see the file COPYING. If not, write to
* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* fsnotify inode mark locking/lifetime/and refcnting
*
* REFCNT:
* The mark->refcnt tells how many "things" in the kernel currently are
* referencing this object. The object typically will live inside the kernel
* with a refcnt of 2, one for each list it is on (i_list, g_list). Any task
* which can find this object holding the appropriete locks, can take a reference
* and the object itself is guaranteed to survive until the reference is dropped.
*
* LOCKING:
* There are 3 spinlocks involved with fsnotify inode marks and they MUST
* be taken in order as follows:
*
* mark->lock
* group->mark_lock
* inode->i_lock
*
* mark->lock protects 2 things, mark->group and mark->inode. You must hold
* that lock to dereference either of these things (they could be NULL even with
* the lock)
*
* group->mark_lock protects the marks_list anchored inside a given group
* and each mark is hooked via the g_list. It also sorta protects the
* free_g_list, which when used is anchored by a private list on the stack of the
* task which held the group->mark_lock.
*
* inode->i_lock protects the i_fsnotify_marks list anchored inside a
* given inode and each mark is hooked via the i_list. (and sorta the
* free_i_list)
*
*
* LIFETIME:
* Inode marks survive between when they are added to an inode and when their
* refcnt==0.
*
* The inode mark can be cleared for a number of different reasons including:
* - The inode is unlinked for the last time. (fsnotify_inode_remove)
* - The inode is being evicted from cache. (fsnotify_inode_delete)
* - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes)
* - Something explicitly requests that it be removed. (fsnotify_destroy_mark)
* - The fsnotify_group associated with the mark is going away and all such marks
* need to be cleaned up. (fsnotify_clear_marks_by_group)
*
* Worst case we are given an inode and need to clean up all the marks on that
* inode. We take i_lock and walk the i_fsnotify_marks safely. For each
* mark on the list we take a reference (so the mark can't disappear under us).
* We remove that mark form the inode's list of marks and we add this mark to a
* private list anchored on the stack using i_free_list; At this point we no
* longer fear anything finding the mark using the inode's list of marks.
*
* We can safely and locklessly run the private list on the stack of everything
* we just unattached from the original inode. For each mark on the private list
* we grab the mark-> and can thus dereference mark->group and mark->inode. If
* we see the group and inode are not NULL we take those locks. Now holding all
* 3 locks we can completely remove the mark from other tasks finding it in the
* future. Remember, 10 things might already be referencing this mark, but they
* better be holding a ref. We drop our reference we took before we unhooked it
* from the inode. When the ref hits 0 we can free the mark.
*
* Very similarly for freeing by group, except we use free_g_list.
*
* This has the very interesting property of being able to run concurrently with
* any (or all) other directions.
*/
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/srcu.h>
#include <linux/atomic.h>
#include <linux/fsnotify_backend.h>
#include "fsnotify.h"
struct srcu_struct fsnotify_mark_srcu;
static DEFINE_SPINLOCK(destroy_lock);
static LIST_HEAD(destroy_list);
static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);
void fsnotify_get_mark(struct fsnotify_mark *mark)
{
atomic_inc(&mark->refcnt);
}
void fsnotify_put_mark(struct fsnotify_mark *mark)
{
if (atomic_dec_and_test(&mark->refcnt)) {
if (mark->group)
fsnotify_put_group(mark->group);
mark->free_mark(mark);
}
}
/*
* Any time a mark is getting freed we end up here.
* The caller had better be holding a reference to this mark so we don't actually
* do the final put under the mark->lock
*/
void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
struct fsnotify_group *group)
{
struct inode *inode = NULL;
BUG_ON(!mutex_is_locked(&group->mark_mutex));
spin_lock(&mark->lock);
/* something else already called this function on this mark */
if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
spin_unlock(&mark->lock);
return;
}
mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
inode = mark->i.inode;
fsnotify_destroy_inode_mark(mark);
} else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
fsnotify_destroy_vfsmount_mark(mark);
else
BUG();
list_del_init(&mark->g_list);
spin_unlock(&mark->lock);
if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
iput(inode);
/* release lock temporarily */
mutex_unlock(&group->mark_mutex);
spin_lock(&destroy_lock);
list_add(&mark->destroy_list, &destroy_list);
spin_unlock(&destroy_lock);
wake_up(&destroy_waitq);
/*
* We don't necessarily have a ref on mark from caller so the above destroy
* may have actually freed it, unless this group provides a 'freeing_mark'
* function which must be holding a reference.
*/
/*
* Some groups like to know that marks are being freed. This is a
* callback to the group function to let it know that this mark
* is being freed.
*/
if (group->ops->freeing_mark)
group->ops->freeing_mark(mark, group);
/*
* __fsnotify_update_child_dentry_flags(inode);
*
* I really want to call that, but we can't, we have no idea if the inode
* still exists the second we drop the mark->lock.
*
* The next time an event arrive to this inode from one of it's children
* __fsnotify_parent will see that the inode doesn't care about it's
* children and will update all of these flags then. So really this
* is just a lazy update (and could be a perf win...)
*/
atomic_dec(&group->num_marks);
mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
}
void fsnotify_destroy_mark(struct fsnotify_mark *mark,
struct fsnotify_group *group)
{
mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
fsnotify_destroy_mark_locked(mark, group);
mutex_unlock(&group->mark_mutex);
}
void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
{
assert_spin_locked(&mark->lock);
mark->mask = mask;
if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
fsnotify_set_inode_mark_mask_locked(mark, mask);
}
void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask)
{
assert_spin_locked(&mark->lock);
mark->ignored_mask = mask;
}
/*
* Attach an initialized mark to a given group and fs object.
* These marks may be used for the fsnotify backend to determine which
* event types should be delivered to which group.
*/
int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
struct fsnotify_group *group, struct inode *inode,
struct vfsmount *mnt, int allow_dups)
{
int ret = 0;
BUG_ON(inode && mnt);
BUG_ON(!inode && !mnt);
BUG_ON(!mutex_is_locked(&group->mark_mutex));
/*
* LOCKING ORDER!!!!
* group->mark_mutex
* mark->lock
* inode->i_lock
*/
spin_lock(&mark->lock);
mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;
fsnotify_get_group(group);
mark->group = group;
list_add(&mark->g_list, &group->marks_list);
atomic_inc(&group->num_marks);
fsnotify_get_mark(mark); /* for i_list and g_list */
if (inode) {
ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
if (ret)
goto err;
} else if (mnt) {
ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups);
if (ret)
goto err;
} else {
BUG();
}
/* this will pin the object if appropriate */
fsnotify_set_mark_mask_locked(mark, mark->mask);
spin_unlock(&mark->lock);
if (inode)
__fsnotify_update_child_dentry_flags(inode);
return ret;
err:
mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
list_del_init(&mark->g_list);
fsnotify_put_group(group);
mark->group = NULL;
atomic_dec(&group->num_marks);
spin_unlock(&mark->lock);
spin_lock(&destroy_lock);
list_add(&mark->destroy_list, &destroy_list);
spin_unlock(&destroy_lock);
wake_up(&destroy_waitq);
return ret;
}
int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group,
struct inode *inode, struct vfsmount *mnt, int allow_dups)
{
int ret;
mutex_lock(&group->mark_mutex);
ret = fsnotify_add_mark_locked(mark, group, inode, mnt, allow_dups);
mutex_unlock(&group->mark_mutex);
return ret;
}
/*
* clear any marks in a group in which mark->flags & flags is true
*/
void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
unsigned int flags)
{
struct fsnotify_mark *lmark, *mark;
mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
if (mark->flags & flags) {
fsnotify_get_mark(mark);
fsnotify_destroy_mark_locked(mark, group);
fsnotify_put_mark(mark);
}
}
mutex_unlock(&group->mark_mutex);
}
/*
* Given a group, destroy all of the marks associated with that group.
*/
void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
{
fsnotify_clear_marks_by_group_flags(group, (unsigned int)-1);
}
void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
{
assert_spin_locked(&old->lock);
new->i.inode = old->i.inode;
new->m.mnt = old->m.mnt;
if (old->group)
fsnotify_get_group(old->group);
new->group = old->group;
new->mask = old->mask;
new->free_mark = old->free_mark;
}
/*
* Nothing fancy, just initialize lists and locks and counters.
*/
void fsnotify_init_mark(struct fsnotify_mark *mark,
void (*free_mark)(struct fsnotify_mark *mark))
{
memset(mark, 0, sizeof(*mark));
spin_lock_init(&mark->lock);
atomic_set(&mark->refcnt, 1);
mark->free_mark = free_mark;
}
static int fsnotify_mark_destroy(void *ignored)
{
struct fsnotify_mark *mark, *next;
LIST_HEAD(private_destroy_list);
for (;;) {
spin_lock(&destroy_lock);
/* exchange the list head */
list_replace_init(&destroy_list, &private_destroy_list);
spin_unlock(&destroy_lock);
synchronize_srcu(&fsnotify_mark_srcu);
list_for_each_entry_safe(mark, next, &private_destroy_list, destroy_list) {
list_del_init(&mark->destroy_list);
fsnotify_put_mark(mark);
}
wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
}
return 0;
}
static int __init fsnotify_mark_init(void)
{
struct task_struct *thread;
thread = kthread_run(fsnotify_mark_destroy, NULL,
"fsnotify_mark");
if (IS_ERR(thread))
panic("unable to start fsnotify mark destruction thread.");
return 0;
}
device_initcall(fsnotify_mark_init);