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 <t...@kernel.org>
---
include/linux/workqueue.h | 8 +++++---
kernel/workqueue.c | 20 +++++++++++---------
2 files changed, 16 insertions(+), 12 deletions(-)
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 83755f4..093968e 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -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)
\
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 11723c5..9087599 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1041,16 +1041,14 @@ 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)
@@ -1065,6 +1063,11 @@ 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;
}
@@ -1318,9 +1321,8 @@ 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);
@@ -1429,7 +1431,7 @@ 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,
--
1.7.7.3
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