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Commit 57b30ae7 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: reimplement cancel_delayed_work() using try_to_grab_pending() 



cancel_delayed_work() can't be called from IRQ handlers due to its use
of del_timer_sync() and can't cancel work items which are already
transferred from timer to worklist.

Also, unlike other flush and cancel functions, a canceled delayed_work
would still point to the last associated cpu_workqueue.  If the
workqueue is destroyed afterwards and the work item is re-used on a
different workqueue, the queueing code can oops trying to dereference
already freed cpu_workqueue.

This patch reimplements cancel_delayed_work() using
try_to_grab_pending() and set_work_cpu_and_clear_pending().  This
allows the function to be called from IRQ handlers and makes its
behavior consistent with other flush / cancel functions.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
parent e7c2f967

include/linux/workqueue.h

+1 −16
Original line number Diff line number Diff line
@@ -420,6 +420,7 @@ extern bool flush_work(struct work_struct *work); 
extern bool cancel_work_sync(struct work_struct *work);



extern bool flush_delayed_work(struct delayed_work *dwork);

extern bool cancel_delayed_work(struct delayed_work *dwork);

extern bool cancel_delayed_work_sync(struct delayed_work *dwork);



extern void workqueue_set_max_active(struct workqueue_struct *wq,
@@ -428,22 +429,6 @@ extern bool workqueue_congested(unsigned int cpu, struct workqueue_struct *wq); 
extern unsigned int work_cpu(struct work_struct *work);

extern unsigned int work_busy(struct work_struct *work);



/*

 * Kill off a pending schedule_delayed_work().  Note that the work callback

 * function may still be running on return from cancel_delayed_work(), unless

 * it returns 1 and the work doesn't re-arm itself. Run flush_workqueue() or

 * cancel_work_sync() to wait on it.

 */

static inline bool cancel_delayed_work(struct delayed_work *work)

{

	bool ret;



	ret = del_timer_sync(&work->timer);

	if (ret)

		work_clear_pending(&work->work);

	return ret;

}



/*

 * Like above, but uses del_timer() instead of del_timer_sync(). This means,

 * if it returns 0 the timer function may be running and the queueing is in

kernel/workqueue.c

+30 −0
Original line number Diff line number Diff line
@@ -2948,6 +2948,36 @@ bool flush_delayed_work(struct delayed_work *dwork) 
}

EXPORT_SYMBOL(flush_delayed_work);



/**

 * cancel_delayed_work - cancel a delayed work

 * @dwork: delayed_work to cancel

 *

 * Kill off a pending delayed_work.  Returns %true if @dwork was pending

 * and canceled; %false if wasn't pending.  Note that the work callback

 * function may still be running on return, unless it returns %true and the

 * work doesn't re-arm itself.  Explicitly flush or use

 * cancel_delayed_work_sync() to wait on it.

 *

 * This function is safe to call from any context including IRQ handler.

 */

bool cancel_delayed_work(struct delayed_work *dwork)

{

	unsigned long flags;

	int ret;



	do {

		ret = try_to_grab_pending(&dwork->work, true, &flags);

	} while (unlikely(ret == -EAGAIN));



	if (unlikely(ret < 0))

		return false;



	set_work_cpu_and_clear_pending(&dwork->work, work_cpu(&dwork->work));

	local_irq_restore(flags);

	return true;

}

EXPORT_SYMBOL(cancel_delayed_work);



/**

 * cancel_delayed_work_sync - cancel a delayed work and wait for it to finish

 * @dwork: the delayed work cancel