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Merge tag 'locking_urgent_for_v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull locking fix from Borislav Petkov:
 "Fix ordering in the queued writer lock's slowpath"

* tag 'locking_urgent_for_v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/qrwlock: Fix ordering in queued_write_lock_slowpath()
This commit is contained in:
Linus Torvalds
2021-04-25 09:10:10 -07:00
parent 682b26bd80 84a24bf8c5
commit 0146da0d4c
1 changed files with 4 additions and 3 deletions
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7
kernel/locking/qrwlock.c
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@@ -60,6 +60,8 @@ EXPORT_SYMBOL(queued_read_lock_slowpath);
*/ */
void queued_write_lock_slowpath(struct qrwlock *lock) void queued_write_lock_slowpath(struct qrwlock *lock)
{ {
int cnts;
/* Put the writer into the wait queue */ /* Put the writer into the wait queue */
arch_spin_lock(&lock->wait_lock); arch_spin_lock(&lock->wait_lock);
@@ -73,9 +75,8 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
/* When no more readers or writers, set the locked flag */ /* When no more readers or writers, set the locked flag */
do { do {
atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING); cnts = atomic_cond_read_relaxed(&lock->cnts, VAL == _QW_WAITING);
} while (atomic_cmpxchg_relaxed(&lock->cnts, _QW_WAITING, } while (!atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED));
_QW_LOCKED) != _QW_WAITING);
unlock: unlock:
arch_spin_unlock(&lock->wait_lock); arch_spin_unlock(&lock->wait_lock);
} }