Commit d566c786 authored by Waiman Long's avatar Waiman Long Committed by Ingo Molnar
Browse files

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: default avatarWaiman Long <longman@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarBoqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20240222150540.79981-4-longman@redhat.com
parent d6cac0b6

kernel/locking/rwsem.c

+3 −3
Original line number Diff line number Diff line
@@ -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))