From: Stephen Boyd <sboyd@codeaurora.org>
To: Yong Zhang <yong.zhang0@gmail.com>
Cc: linux-kernel@vger.kernel.org, Tejun Heo <tj@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 11:36:32 -0700 [thread overview]
Message-ID: <4F905B30.4080501@codeaurora.org> (raw)
In-Reply-To: <20120419081002.GB3963@zhy>
On 04/19/12 01:10, Yong Zhang wrote:
> On Wed, Apr 18, 2012 at 08:25:57PM -0700, Stephen Boyd wrote:
>> If a workqueue is flushed but the work item is not scheduled to
>> run, lockdep checking will be circumvented. For example:
>>
>> static DEFINE_MUTEX(mutex);
>>
>> static void my_work(struct work_struct *w)
>> {
>> mutex_lock(&mutex);
>> mutex_unlock(&mutex);
>> }
>>
>> static DECLARE_WORK(work, my_work);
>>
>> static int __init start_test_module(void)
>> {
>> schedule_work(&work);
>> return 0;
>> }
>> module_init(start_test_module);
>>
>> static void __exit stop_test_module(void)
>> {
>> mutex_lock(&mutex);
>> flush_work(&work);
>> mutex_unlock(&mutex);
>> }
>> module_exit(stop_test_module);
>>
>> would only print a warning if the work item was actively running
>> when flush_work() was called. Otherwise flush_work() returns
>> early. In this trivial example nothing could go wrong, but if the
>> work item is schedule via an interrupt we could potentially have a
>> scenario where the work item is running just at the time flush_work()
> You mean flush_work() could be called in interupt? I don't it is
> possible.
No.
>
>> is called. This could become a classic AB-BA locking problem.
> I don't see how the deadlock happen, could you please be more
> specific?
>
Does looking at the second patch help? Basically schedule_work() can run
the callback right between the time the mutex is acquired and
flush_work() is called:
CPU0 CPU1
<irq>
schedule_work() mutex_lock(&mutex)
<irq return>
my_work() flush_work()
mutex_lock(&mutex)
<deadlock>
--
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 18:36 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 [this message]
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
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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