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: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 1 insertions, 16 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index d86b320319e0..4898289564ab 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -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,
@@ -429,22 +430,6 @@ 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
  * progress.