linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Tejun Heo <tj@kernel.org>
To: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: [PATCH -stable] workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic
Date: Tue, 4 Sep 2012 16:58:12 -0700	[thread overview]
Message-ID: <20120904235812.GA2836@dhcp-172-17-108-109.mtv.corp.google.com> (raw)
In-Reply-To: <20120904233901.GC9092@dhcp-172-17-108-109.mtv.corp.google.com>

From: Lai Jiangshan <laijs@cn.fujitsu.com>

The compiler may compile the following code into TWO write/modify
instructions.

        worker->flags &= ~WORKER_UNBOUND;
        worker->flags |= WORKER_REBIND;

so the other CPU may temporarily see worker->flags which doesn't have
either WORKER_UNBOUND or WORKER_REBIND set and perform local wakeup
prematurely.

Fix it by using single explicit assignment via ACCESS_ONCE().

Because idle workers have another WORKER_NOT_RUNNING flag, this bug
doesn't exist for them; however, update it to use the same pattern for
consistency.

tj: Applied the change to idle workers too and updated comments and
    patch description a bit.

stable: Idle worker rebinding doesn't apply for -stable and
        WORKER_UNBOUND used to be WORKER_ROGUE.  Updated accordingly.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org
---
 kernel/workqueue.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9a3128d..d7eb05a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3441,14 +3441,17 @@ static int __cpuinit trustee_thread(void *__gcwq)
 
 	for_each_busy_worker(worker, i, pos, gcwq) {
 		struct work_struct *rebind_work = &worker->rebind_work;
+		unsigned long worker_flags = worker->flags;
 
 		/*
 		 * Rebind_work may race with future cpu hotplug
 		 * operations.  Use a separate flag to mark that
-		 * rebinding is scheduled.
+		 * rebinding is scheduled.  The morphing should
+		 * be atomic.
 		 */
-		worker->flags |= WORKER_REBIND;
-		worker->flags &= ~WORKER_ROGUE;
+		worker_flags |= WORKER_REBIND;
+		worker_flags &= ~WORKER_ROGUE;
+		ACCESS_ONCE(worker->flags) = worker_flags;
 
 		/* queue rebind_work, wq doesn't matter, use the default one */
 		if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,

  reply	other threads:[~2012-09-04 23:58 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 ` [PATCH 01/10 V4] workqueue: ensure the wq_worker_sleeping() see the right flags Lai Jiangshan
2012-09-04 23:39   ` [PATCH] workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic Tejun Heo
2012-09-04 23:58     ` Tejun Heo [this message]
2012-09-16 15:49       ` [PATCH -stable] " 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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20120904235812.GA2836@dhcp-172-17-108-109.mtv.corp.google.com \
    --to=tj@kernel.org \
    --cc=laijs@cn.fujitsu.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=stable@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).