Messages in this thread | | | Date | Tue, 27 Apr 2021 08:56:59 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] locking/qrwlock: queued_write_lock_slowpath() cleanup |
| |
On Mon, Apr 26, 2021 at 02:50:17PM -0400, Waiman Long wrote: > 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.
Right, there's no functional change here.
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> > Signed-off-by: Waiman Long <longman@redhat.com> > --- > 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 b94f3831e963..ec36b73f4733 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);
Acked-by: Will Deacon <will@kernel.org>
Will
| |