From: Stephen Boyd <sboyd@codeaurora.org>
To: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
Ben Dooks <ben-linux@fluff.org>
Subject: Re: [PATCH 1/2] workqueue: Catch more locking problems with flush_work()
Date: Thu, 19 Apr 2012 11:10:41 -0700 [thread overview]
Message-ID: <4F905521.9020901@codeaurora.org> (raw)
In-Reply-To: <20120419152841.GA10553@google.com>
On 04/19/12 08:28, Tejun Heo wrote:
> On Wed, Apr 18, 2012 at 08:25:57PM -0700, Stephen Boyd wrote:
>> @@ -2513,8 +2513,11 @@ bool flush_work(struct work_struct *work)
>> wait_for_completion(&barr.done);
>> destroy_work_on_stack(&barr.work);
>> return true;
>> - } else
>> + } else {
>> + lock_map_acquire(&work->lockdep_map);
>> + lock_map_release(&work->lockdep_map);
>> return false;
> We don't have this annotation when start_flush_work() succeeds either,
> right? IOW, would lockdep trigger when an actual deadlock happens?
I believe it does although I haven't tested it.
> If not, why not add the acquire/release() before flush_work() does
> anything?
>
I was worried about causing false positive lockdep warnings in the case
that start_flush_work() succeeds and returns true. In that case, lockdep
is told about the cwq lockdep map:
static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
bool wait_executing)
{
.....
if (cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER)
lock_map_acquire(&cwq->wq->lockdep_map);
else
lock_map_acquire_read(&cwq->wq->lockdep_map);
and so if we acquired the work->lockdep_map before the
cwq->wq->lockdep_map we would get a warning about ABBA between these two
lockdep maps. At least that is what I'm lead to believe when I look at
what process_one_work() is doing. Please correct me if I'm wrong.
--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
next prev parent reply other threads:[~2012-04-19 18:10 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-19 3:25 [PATCH 1/2] workqueue: Catch more locking problems with flush_work() Stephen Boyd
2012-04-19 3:25 ` [PATCH 2/2] ks8851: Fix mutex deadlock in ks8851_net_stop() Stephen Boyd
2012-04-21 19:34 ` David Miller
2012-04-19 8:10 ` [PATCH 1/2] workqueue: Catch more locking problems with flush_work() Yong Zhang
2012-04-19 18:36 ` Stephen Boyd
2012-04-20 5:26 ` Yong Zhang
2012-04-20 6:01 ` Yong Zhang
2012-04-20 6:26 ` Stephen Boyd
2012-04-20 7:18 ` Yong Zhang
2012-04-20 8:18 ` Stephen Boyd
2012-04-20 8:32 ` Yong Zhang
2012-04-21 0:32 ` Yong Zhang
2012-04-19 15:28 ` Tejun Heo
2012-04-19 18:10 ` Stephen Boyd [this message]
2012-04-20 17:35 ` Tejun Heo
2012-04-20 23:15 ` Stephen Boyd
2012-04-21 0:28 ` [PATCHv2] " Stephen Boyd
2012-04-21 0:34 ` Yong Zhang
2012-04-23 18:07 ` Tejun Heo
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