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 {
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