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locking/rwsem: No need to check for handoff bit if wait queue empty

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Since commit d257cc8cb8 ("locking/rwsem: Make handoff bit handling
more consistent"), the handoff bit is always cleared if the wait queue
becomes empty. There is no need to check for RWSEM_FLAG_HANDOFF when
the wait list is known to be empty.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220322152059.2182333-2-longman@redhat.com
This commit is contained in:
Waiman Long 2022-03-22 11:20:57 -04:00 committed by Peter Zijlstra
parent 8b023accc8
commit f9e21aa9e6
1 changed files with 4 additions and 5 deletions
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9
kernel/locking/rwsem.c
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@ -977,12 +977,11 @@ queue:
if (list_empty(&sem->wait_list)) {
/*
* In case the wait queue is empty and the lock isn't owned
* by a writer or has the handoff bit set, this reader can
* exit the slowpath and return immediately as its
* RWSEM_READER_BIAS has already been set in the count.
* by a writer, this reader can exit the slowpath and return
* immediately as its RWSEM_READER_BIAS has already been set
* in the count.
*/
if (!(atomic_long_read(&sem->count) &
(RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {
if (!(atomic_long_read(&sem->count) & RWSEM_WRITER_MASK)) {
/* Provide lock ACQUIRE */
smp_acquire__after_ctrl_dep();
raw_spin_unlock_irq(&sem->wait_lock);