forked from Minki/linux
d8d0da4eee
include/asm-generic/qrwlock.h was trying to get arch_spin_is_locked via
asm-generic/qspinlock.h. However, this does not work because architectures
might be using queued rwlocks but not queued spinlocks (csky), or because they
might be defining their own queued_* macros before including asm/qspinlock.h.
To fix this, ensure that asm/spinlock.h always includes qrwlock.h after
defining arch_spin_is_locked (either directly for csky, or via
asm/qspinlock.h for other architectures). The only inclusion elsewhere
is in kernel/locking/qrwlock.c. That one is really unnecessary because
the file is only compiled in SMP configurations (config QUEUED_RWLOCKS
depends on SMP) and in that case linux/spinlock.h already includes
asm/qrwlock.h if needed, via asm/spinlock.h.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Waiman Long <longman@redhat.com>
Fixes: 26128cb6c7 ("locking/rwlocks: Add contention detection for rwlocks")
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Ben Gardon <bgardon@google.com>
[Add arch/sparc and kernel/locking parts per discussion with Waiman. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
83 lines
2.3 KiB
C
83 lines
2.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Queued read/write locks
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*
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* (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
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*
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* Authors: Waiman Long <waiman.long@hp.com>
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*/
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#include <linux/smp.h>
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#include <linux/bug.h>
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#include <linux/cpumask.h>
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#include <linux/percpu.h>
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#include <linux/hardirq.h>
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#include <linux/spinlock.h>
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/**
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* queued_read_lock_slowpath - acquire read lock of a queue rwlock
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* @lock: Pointer to queue rwlock structure
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*/
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void queued_read_lock_slowpath(struct qrwlock *lock)
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{
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/*
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* Readers come here when they cannot get the lock without waiting
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*/
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if (unlikely(in_interrupt())) {
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/*
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* Readers in interrupt context will get the lock immediately
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* if the writer is just waiting (not holding the lock yet),
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* so spin with ACQUIRE semantics until the lock is available
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* without waiting in the queue.
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*/
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atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
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return;
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}
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atomic_sub(_QR_BIAS, &lock->cnts);
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/*
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* Put the reader into the wait queue
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*/
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arch_spin_lock(&lock->wait_lock);
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atomic_add(_QR_BIAS, &lock->cnts);
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/*
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* The ACQUIRE semantics of the following spinning code ensure
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* that accesses can't leak upwards out of our subsequent critical
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* section in the case that the lock is currently held for write.
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*/
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atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
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/*
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* Signal the next one in queue to become queue head
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*/
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arch_spin_unlock(&lock->wait_lock);
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}
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EXPORT_SYMBOL(queued_read_lock_slowpath);
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/**
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* queued_write_lock_slowpath - acquire write lock of a queue rwlock
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* @lock : Pointer to queue rwlock structure
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*/
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void queued_write_lock_slowpath(struct qrwlock *lock)
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{
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/* Put the writer into the wait queue */
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arch_spin_lock(&lock->wait_lock);
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/* Try to acquire the lock directly if no reader is present */
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if (!atomic_read(&lock->cnts) &&
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(atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0))
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goto unlock;
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/* Set the waiting flag to notify readers that a writer is pending */
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atomic_add(_QW_WAITING, &lock->cnts);
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/* When no more readers or writers, set the locked flag */
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do {
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atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING);
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} while (atomic_cmpxchg_relaxed(&lock->cnts, _QW_WAITING,
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_QW_LOCKED) != _QW_WAITING);
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unlock:
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arch_spin_unlock(&lock->wait_lock);
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}
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EXPORT_SYMBOL(queued_write_lock_slowpath);
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