linux-kernel - [PATCH v3 2/4] locking/rwsem: Don't wake up one's own task

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Message-Id: <1463093811-10684-3-git-send-email-Waiman.Long@hpe.com>
Date:	Thu, 12 May 2016 18:56:49 -0400
From:	Waiman Long <Waiman.Long@....com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
	Jason Low <jason.low2@...com>,
	Dave Chinner <david@...morbit.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>,
	Waiman Long <Waiman.Long@....com>
Subject: [PATCH v3 2/4] locking/rwsem: Don't wake up one's own task

As rwsem_down_read_failed() will queue itself and potentially call
__rwsem_do_wake(sem, RWSEM_WAKE_ANY), it is possible that a reader
will try to wake up its own task. This patch adds a check to make
sure that this won't happen.

Signed-off-by: Waiman Long <Waiman.Long@....com>
---
 kernel/locking/rwsem-xadd.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 7ccab5c..22f7d58 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -202,7 +202,8 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type)
 		 */
 		smp_mb();
 		waiter->task = NULL;
-		wake_up_process(tsk);
+		if (tsk != current)
+			wake_up_process(tsk);
 		put_task_struct(tsk);
 	} while (--loop);
 
-- 
1.7.1