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From: Lai Jiangshan <laijs@cn.fujitsu.com>
To: Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Subject: [PATCH 01/10 V4] workqueue: ensure the wq_worker_sleeping() see the right flags
Date: Sun, 2 Sep 2012 00:28:19 +0800	[thread overview]
Message-ID: <1346516916-1991-2-git-send-email-laijs@cn.fujitsu.com> (raw)
In-Reply-To: <1346516916-1991-1-git-send-email-laijs@cn.fujitsu.com>

The compiler may compile this code into TWO write/modify instructions.
		worker->flags &= ~WORKER_UNBOUND;
		worker->flags |= WORKER_REBIND;

so the other CPU may see the temporary of worker->flags which has
not WORKER_UNBOUND nor WORKER_REBIND, it will wrongly do local wake up.

so we use one write/modify instruction explicitly instead.

This bug will not occur on idle workers, because they have another
WORKER_NOT_RUNNING flags.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
 kernel/workqueue.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 692d976..4f252d0 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1434,10 +1434,13 @@ retry:
 	/* rebind busy workers */
 	for_each_busy_worker(worker, i, pos, gcwq) {
 		struct work_struct *rebind_work = &worker->rebind_work;
+		unsigned long worker_flags = worker->flags;
 
 		/* morph UNBOUND to REBIND */
-		worker->flags &= ~WORKER_UNBOUND;
-		worker->flags |= WORKER_REBIND;
+		worker_flags &= ~WORKER_UNBOUND;
+		worker_flags |= WORKER_REBIND;
+		/* ensure the wq_worker_sleeping() see the right flags */
+		ACCESS_ONCE(worker->flags) = worker_flags;
 
 		if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
 				     work_data_bits(rebind_work)))
-- 
1.7.4.4


  reply	other threads:[~2012-09-01 17:44 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-01 16:28 [PATCH 00/10 V4] workqueue: fix and cleanup hotplug/rebind_workers() Lai Jiangshan
2012-09-01 16:28 ` Lai Jiangshan [this message]
2012-09-04 23:39   ` [PATCH] workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic Tejun Heo
2012-09-04 23:58     ` [PATCH -stable] " Tejun Heo
2012-09-16 15:49       ` Ben Hutchings
2012-09-05  1:05     ` [PATCH] " Lai Jiangshan
2012-09-05  1:17       ` Tejun Heo
2012-09-01 16:28 ` [PATCH 02/10 V4] workqueue: fix deadlock in rebind_workers() Lai Jiangshan
2012-09-05  0:54   ` Tejun Heo
2012-09-05  1:28     ` Lai Jiangshan
2012-09-05  1:33       ` Tejun Heo
2012-09-01 16:28 ` [PATCH 03/10 V4] workqueue: add POOL_MANAGING_WORKERS Lai Jiangshan
2012-09-01 16:28 ` [PATCH 04/10 V4] workqueue: add manage_workers_slowpath() Lai Jiangshan
2012-09-05  1:12   ` Tejun Heo
2012-09-06  1:55     ` Lai Jiangshan
2012-09-01 16:28 ` [PATCH 05/10 V4] workqueue: move rebind_hold to idle_rebind Lai Jiangshan
2012-09-01 16:28 ` [PATCH 06/10 V4] workqueue: simple clear WORKER_REBIND Lai Jiangshan
2012-09-01 16:28 ` [PATCH 07/10 V4] workqueue: move idle_rebind pointer to gcwq Lai Jiangshan
2012-09-01 16:28 ` [PATCH 08/10 V4] workqueue: explicit way to wait for idles workers to finish Lai Jiangshan
2012-09-01 16:28 ` [PATCH 09/10] workqueue: single pass rebind_workers Lai Jiangshan
2012-09-01 16:28 ` [PATCH 10/10 V4] workqueue: merge the role of rebind_hold to idle_done Lai Jiangshan
2012-09-05  1:15   ` Tejun Heo
2012-09-05  1:48     ` Lai Jiangshan

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