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

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 2340b6d..c6d17ae 100644 (file)
--- 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))