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workqueue: use irqsafe timer for delayed_work

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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: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2012-08-21 13:18:24 -07:00
commit e0aecdd874
2 changed files with 16 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

8
include/linux/workqueue.h
View file

@ -136,7 +136,8 @@ struct execute_work {
#define __DELAYED_WORK_INITIALIZER(n, f, tflags) { \
.work = __WORK_INITIALIZER((n).work, (f)), \
.timer = __TIMER_INITIALIZER(delayed_work_timer_fn, \
0, (unsigned long)&(n), (tflags)), \
0, (unsigned long)&(n), \
(tflags) | TIMER_IRQSAFE), \
}
#define DECLARE_WORK(n, f) \
@ -214,7 +215,8 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; }
do { \
INIT_WORK(&(_work)->work, (_func)); \
__setup_timer(&(_work)->timer, delayed_work_timer_fn, \
(unsigned long)(_work), (_tflags)); \
(unsigned long)(_work), \
(_tflags) | TIMER_IRQSAFE); \
} while (0)
#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, \
delayed_work_timer_fn, \
(unsigned long)(_work), \
(_tflags)); \
(_tflags) | TIMER_IRQSAFE); \
} while (0)
#define INIT_DELAYED_WORK(_work, _func) \

20
kernel/workqueue.c
View file

@ -1048,16 +1048,14 @@ static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color,
* for arbitrarily long
*
* On >= 0 return, the caller owns @work's PENDING bit. To avoid getting
* preempted while holding PENDING and @work off queue, preemption must be
* disabled on entry. This ensures that we don't return -EAGAIN while
* another task is preempted in this function.
* interrupted while holding PENDING and @work off queue, irq must be
* disabled on entry. This, combined with delayed_work->timer being
* irqsafe, ensures that we return -EAGAIN for finite short period of time.
*
* On successful return, >= 0, irq is disabled and the caller is
* responsible for releasing it using local_irq_restore(*@flags).
*
* This function is safe to call from any context other than IRQ handler.
* An IRQ handler may run on top of delayed_work_timer_fn() which can make
* this function return -EAGAIN perpetually.
* This function is safe to call from any context including IRQ handler.
*/
static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
unsigned long *flags)
@ -1072,6 +1070,11 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
if (is_dwork) {
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)))
return 1;
}
@ -1327,9 +1330,8 @@ void delayed_work_timer_fn(unsigned long __data)
struct delayed_work *dwork = (struct delayed_work *)__data;
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);
local_irq_enable();
}
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
* 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.
*/
bool mod_delayed_work_on(int cpu, struct workqueue_struct *wq,