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Date: Thu, 19 Apr 2012 11:36:32 -0700 From: Stephen Boyd <sboyd@...eaurora.org> To: Yong Zhang <yong.zhang0@...il.com> CC: linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>, netdev@...r.kernel.org, Ben Dooks <ben-linux@...ff.org> Subject: Re: [PATCH 1/2] workqueue: Catch more locking problems with flush_work() 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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