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: Tejun Heo <tj@kernel.org>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 85bd340..b394df8 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1048,16 +1048,14 @@
* 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 @@
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 @@
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 @@
* 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,