From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org, Davidlohr Bueso <dave@stgolabs.net>,
Phil Auld <pauld@redhat.com>, Waiman Long <longman@redhat.com>
Subject: [PATCH 4/5] locking/rwsem: Wake up all waiting readers if RWSEM_WAKE_READ_OWNED
Date: Tue, 17 Nov 2020 22:04:28 -0500 [thread overview]
Message-ID: <20201118030429.23017-5-longman@redhat.com> (raw)
In-Reply-To: <20201118030429.23017-1-longman@redhat.com>
The rwsem wakeup logic has been modified by commit d3681e269fff
("locking/rwsem: Wake up almost all readers in wait queue") to wake up
all readers in the wait queue if the first waiter is a reader. In the
case of RWSEM_WAKE_READ_OWNED, not all readers can be woken up if the
first waiter happens to be a writer. Complete the logic by waking up
all readers even for this case.
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/rwsem.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 930dd4af3639..23654e3950b5 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -426,7 +426,12 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
lockevent_inc(rwsem_wake_writer);
}
- return;
+ /*
+ * If rwsem has already been owned by reader, wake up other
+ * readers in the wait queue even if first one is a writer.
+ */
+ if (wake_type != RWSEM_WAKE_READ_OWNED)
+ return;
}
/*
@@ -1052,8 +1057,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state, long count)
if (rwsem_optimistic_spin(sem, false)) {
/* rwsem_optimistic_spin() implies ACQUIRE on success */
/*
- * Wake up other readers in the wait list if the front
- * waiter is a reader.
+ * Wake up other readers in the wait queue.
*/
wake_readers:
if ((atomic_long_read(&sem->count) & RWSEM_FLAG_WAITERS)) {
--
2.18.1
next prev parent reply other threads:[~2020-11-18 3:05 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-18 3:04 [PATCH 0/5] locking/rwsem: Rework reader optimistic spinning Waiman Long
2020-11-18 3:04 ` [PATCH 1/5] locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath() Waiman Long
2020-11-18 3:04 ` [PATCH 2/5] locking/rwsem: Prevent potential lock starvation Waiman Long
2020-11-20 14:44 ` Peter Zijlstra
2020-11-20 17:27 ` Waiman Long
2020-11-18 3:04 ` [PATCH 3/5] locking/rwsem: Enable reader optimistic lock stealing Waiman Long
2020-11-20 14:36 ` Peter Zijlstra
2020-11-20 17:26 ` Waiman Long
2020-12-08 3:53 ` Davidlohr Bueso
2020-11-18 3:04 ` Waiman Long [this message]
2020-11-18 4:53 ` [PATCH 4/5] locking/rwsem: Wake up all waiting readers if RWSEM_WAKE_READ_OWNED Davidlohr Bueso
2020-11-19 18:37 ` Waiman Long
2020-11-18 3:04 ` [RFC PATCH 5/5] locking/rwsem: Remove reader optimistic spinning Waiman Long
2020-11-18 5:35 ` Davidlohr Bueso
2020-11-19 18:40 ` Waiman Long
2020-11-20 13:11 ` David Laight
2020-11-20 17:04 ` Waiman Long
2020-11-20 17:37 ` David Laight
2020-11-20 21:38 ` Davidlohr Bueso
2020-11-21 11:50 ` David Laight
2020-11-20 14:44 ` Peter Zijlstra
2020-11-20 22:39 ` Waiman Long
2020-11-20 14:42 ` Peter Zijlstra
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