The following commit has been merged into the locking/urgent branch of tip:
Commit-ID: 28ce0e70ecc30cc7d558a0304e6b816d70848f9a
Gitweb: https://git.kernel.org/tip/28ce0e70ecc30cc7d558a0304e6b816d70848f9a
Author: Waiman Long <longman@xxxxxxxxxx>
AuthorDate: Mon, 26 Apr 2021 14:50:17 -04:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 06 May 2021 15:33:49 +02:00
locking/qrwlock: Cleanup queued_write_lock_slowpath()
Make the code more readable by replacing the atomic_cmpxchg_acquire()
by an equivalent atomic_try_cmpxchg_acquire() and change atomic_add()
to atomic_or().
For architectures that use qrwlock, I do not find one that has an
atomic_add() defined but not an atomic_or(). I guess it should be fine
by changing atomic_add() to atomic_or().
Note that the previous use of atomic_add() isn't wrong as only one
writer that is the wait_lock owner can set the waiting flag and the
flag will be cleared later on when acquiring the write lock.
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Will Deacon <will@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20210426185017.19815-1-longman@xxxxxxxxxx
---
kernel/locking/qrwlock.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
index b94f383..ec36b73 100644
--- a/kernel/locking/qrwlock.c
+++ b/kernel/locking/qrwlock.c
@@ -66,12 +66,12 @@ void queued_write_lock_slowpath(struct qrwlock *lock)
arch_spin_lock(&lock->wait_lock);
/* Try to acquire the lock directly if no reader is present */
- if (!atomic_read(&lock->cnts) &&
- (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0))
+ if (!(cnts = atomic_read(&lock->cnts)) &&
+ atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED))
goto unlock;
/* Set the waiting flag to notify readers that a writer is pending */
- atomic_add(_QW_WAITING, &lock->cnts);
+ atomic_or(_QW_WAITING, &lock->cnts);
/* When no more readers or writers, set the locked flag */
do {
|