Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753313AbZIXSzI (ORCPT ); Thu, 24 Sep 2009 14:55:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752854AbZIXSzH (ORCPT ); Thu, 24 Sep 2009 14:55:07 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:47458 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752101AbZIXSzF (ORCPT ); Thu, 24 Sep 2009 14:55:05 -0400 From: Darren Hart Subject: [PATCH] futex: add memory barrier commentary to futex_wait_queue_me To: linux-kernel@vger.kernel.org Cc: Darren Hart , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Eric Dumazet , Dinakar Guniguntala , John Stultz Date: Thu, 24 Sep 2009 11:54:47 -0700 Message-ID: <20090924185447.694.38948.stgit@Aeon> User-Agent: StGIT/0.14.2 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1343 Lines: 38 The memory barrier semantics of futex_wait_queue_me() are non-obvious. Add some commentary to try and clarify it. Signed-off-by: Darren Hart Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Ingo Molnar CC: Eric Dumazet CC: Dinakar Guniguntala CC: John Stultz --- kernel/futex.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 463af2e..b911adc 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -1656,6 +1656,12 @@ out: static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, struct hrtimer_sleeper *timeout) { + /* + * The task state is guaranteed to be set before another task can + * wake it. set_current_state() is implemented using set_mb() and + * queue_me() calls spin_unlock() upon completion, both serializing + * access to the hash list and forcing another memory barrier. + */ set_current_state(TASK_INTERRUPTIBLE); queue_me(q, hb); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/