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Commit e0aecdd8 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: use irqsafe timer for delayed_work 



Up to now, for delayed_works, try_to_grab_pending() couldn't be used
from IRQ handlers because IRQs may happen while
delayed_work_timer_fn() is in progress leading to indefinite -EAGAIN.

This patch makes delayed_work use the new TIMER_IRQSAFE flag for
delayed_work->timer.  This makes try_to_grab_pending() and thus
mod_delayed_work_on() safe to call from IRQ handlers.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent f991b318

include/linux/workqueue.h

+5 −3
Original line number Original line Diff line number Diff line
@@ -136,7 +136,8 @@ struct execute_work { 
#define __DELAYED_WORK_INITIALIZER(n, f, tflags) {			\

#define __DELAYED_WORK_INITIALIZER(n, f, tflags) {			\

	.work = __WORK_INITIALIZER((n).work, (f)),			\

	.work = __WORK_INITIALIZER((n).work, (f)),			\

	.timer = __TIMER_INITIALIZER(delayed_work_timer_fn,		\

	.timer = __TIMER_INITIALIZER(delayed_work_timer_fn,		\

			0, (unsigned long)&(n), (tflags)),		\

				     0, (unsigned long)&(n),		\

				     (tflags) | TIMER_IRQSAFE),		\

	}

	}





#define DECLARE_WORK(n, f)						\

#define DECLARE_WORK(n, f)						\
@@ -214,7 +215,8 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; } 
	do {								\

	do {								\

		INIT_WORK(&(_work)->work, (_func));			\

		INIT_WORK(&(_work)->work, (_func));			\

		__setup_timer(&(_work)->timer, delayed_work_timer_fn,	\

		__setup_timer(&(_work)->timer, delayed_work_timer_fn,	\

			      (unsigned long)(_work), (_tflags));	\

			      (unsigned long)(_work),			\

			      (_tflags) | TIMER_IRQSAFE);		\

	} while (0)

	} while (0)





#define __INIT_DELAYED_WORK_ONSTACK(_work, _func, _tflags)		\

#define __INIT_DELAYED_WORK_ONSTACK(_work, _func, _tflags)		\
@@ -223,7 +225,7 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; } 
		__setup_timer_on_stack(&(_work)->timer,			\

		__setup_timer_on_stack(&(_work)->timer,			\

				       delayed_work_timer_fn,		\

				       delayed_work_timer_fn,		\

				       (unsigned long)(_work),		\

				       (unsigned long)(_work),		\

				       (_tflags));			\

				       (_tflags) | TIMER_IRQSAFE);	\

	} while (0)

	} while (0)





#define INIT_DELAYED_WORK(_work, _func)					\

#define INIT_DELAYED_WORK(_work, _func)					\

kernel/workqueue.c

+11 −9
Original line number Original line Diff line number Diff line
@@ -1048,16 +1048,14 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color, 
 *		for arbitrarily long

 *		for arbitrarily long

 *

 *

 * On >= 0 return, the caller owns @work's PENDING bit.  To avoid getting

 * On >= 0 return, the caller owns @work's PENDING bit.  To avoid getting

 * preempted while holding PENDING and @work off queue, preemption must be

 * interrupted while holding PENDING and @work off queue, irq must be

 * disabled on entry.  This ensures that we don't return -EAGAIN while

 * disabled on entry.  This, combined with delayed_work->timer being

 * another task is preempted in this function.

 * irqsafe, ensures that we return -EAGAIN for finite short period of time.

 *

 *

 * On successful return, >= 0, irq is disabled and the caller is

 * On successful return, >= 0, irq is disabled and the caller is

 * responsible for releasing it using local_irq_restore(*@flags).

 * responsible for releasing it using local_irq_restore(*@flags).

 *

 *

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

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

 * An IRQ handler may run on top of delayed_work_timer_fn() which can make

 * this function return -EAGAIN perpetually.

 */

 */

static int try_to_grab_pending(struct work_struct *work, bool is_dwork,

static int try_to_grab_pending(struct work_struct *work, bool is_dwork,

			       unsigned long *flags)

			       unsigned long *flags)
@@ -1072,6 +1070,11 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork, 
	if (is_dwork) {

	if (is_dwork) {

		struct delayed_work *dwork = to_delayed_work(work);

		struct delayed_work *dwork = to_delayed_work(work);





		/*

		 * dwork->timer is irqsafe.  If del_timer() fails, it's

		 * guaranteed that the timer is not queued anywhere and not

		 * running on the local CPU.

		 */

		if (likely(del_timer(&dwork->timer)))

		if (likely(del_timer(&dwork->timer)))

			return 1;

			return 1;

	}

	}
@@ -1327,9 +1330,8 @@ void delayed_work_timer_fn(unsigned long __data) 
	struct delayed_work *dwork = (struct delayed_work *)__data;

	struct delayed_work *dwork = (struct delayed_work *)__data;

	struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);

	struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);





	local_irq_disable();

	/* should have been called from irqsafe timer with irq already off */

	__queue_work(dwork->cpu, cwq->wq, &dwork->work);

	__queue_work(dwork->cpu, cwq->wq, &dwork->work);

	local_irq_enable();

}

}

EXPORT_SYMBOL_GPL(delayed_work_timer_fn);

EXPORT_SYMBOL_GPL(delayed_work_timer_fn);
@@ -1444,7 +1446,7 @@ EXPORT_SYMBOL_GPL(queue_delayed_work); 
 * Returns %false if @dwork was idle and queued, %true if @dwork was

 * Returns %false if @dwork was idle and queued, %true if @dwork was

 * pending and its timer was modified.

 * pending and its timer was modified.

 *

 *

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

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

 * See try_to_grab_pending() for details.

 * See try_to_grab_pending() for details.

 */

 */

bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,

bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,