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

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()

1 files changed, 4 insertions, 3 deletions

diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index 4786dd271b45..b94f3831e963 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -60,6 +60,8 @@ EXPORT_SYMBOL(queued_read_lock_slowpath);
  */
 void queued_write_lock_slowpath(struct qrwlock *lock)
 {
+	int cnts;
+
 	/* Put the writer into the wait queue */
 	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 */
 	do {
-		atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING);
-	} while (atomic_cmpxchg_relaxed(&lock->cnts, _QW_WAITING,
-					_QW_LOCKED) != _QW_WAITING);
+		cnts = atomic_cond_read_relaxed(&lock->cnts, VAL == _QW_WAITING);
+	} while (!atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED));
 unlock:
 	arch_spin_unlock(&lock->wait_lock);
 }