[tip: locking/core] locking/rwsem: Clarify that RWSEM_READER_OWNED is just a hint
From: tip-bot2 for Waiman Long
Date: Wed Feb 28 2024 - 07:53:46 EST
The following commit has been merged into the locking/core branch of tip:
Commit-ID: d566c78659eccf085f905fd266fc461de92eaa8f
Gitweb: https://git.kernel.org/tip/d566c78659eccf085f905fd266fc461de92eaa8f
Author: Waiman Long <longman@xxxxxxxxxx>
AuthorDate: Thu, 22 Feb 2024 10:05:39 -05:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 28 Feb 2024 13:08:38 +01:00
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@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Link: https://lore.kernel.org/r/20240222150540.79981-4-longman@xxxxxxxxxx
---
kernel/locking/rwsem.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 2340b6d..c6d17ae 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -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))