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

Since commit d257cc8cb8d5 ("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

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index acde5d6f125463025ab8680da5fa98bffd612cfa..b077b1b2d4b3d42dff5393ad9600ad53ffb4d0c2 100644 (file)
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -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);