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locking/rwsem: Clarify that RWSEM_READER_OWNED is just a hint 

Clarify in the comments that the RWSEM_READER_OWNED bit in the owner
field is just a hint, not an authoritative state of the rwsem.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20240222150540.79981-4-longman@redhat.com
This commit is contained in:
Waiman Long 2024-02-22 10:05:39 -05:00 committed by Ingo Molnar
parent d6cac0b6b0
commit d566c78659
1 changed files with 3 additions and 3 deletions
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6
kernel/locking/rwsem.c
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@ -35,7 +35,7 @@
/*
* The least significant 2 bits of the owner value has the following
* meanings when set.
* - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers
* - Bit 0: RWSEM_READER_OWNED - rwsem may be owned by readers (just a hint)
* - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock
*
* When the rwsem is reader-owned and a spinning writer has timed out,
@ -1002,8 +1002,8 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
/*
* To prevent a constant stream of readers from starving a sleeping
* waiter, don't attempt optimistic lock stealing if the lock is
* currently owned by readers.
* writer, don't attempt optimistic lock stealing if the lock is
* very likely owned by readers.
*/
if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
(rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))