workqueue: make cancel_rearming_delayed_workqueue() work on idle dwork

cancel_rearming_delayed_workqueue(dwork) will hang forever if dwork was not
scheduled, because in that case cancel_delayed_work()->del_timer_sync() never
returns true.

I don't know if there are any callers which may have problems, but this is not
so convenient, and the fix is very simple.

Q: looks like we don't need "struct workqueue_struct *wq" parameter.  If the
timer was aborted successfully, get_wq_data() == wq.  Is it worth to add the
new function?

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 74f3f7825229..ce72d45c7fd8 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -569,6 +569,10 @@ EXPORT_SYMBOL(flush_work_keventd);
 void cancel_rearming_delayed_workqueue(struct workqueue_struct *wq,
                                        struct delayed_work *dwork)
 {
+        /* Was it ever queued ? */
+        if (!get_wq_data(&dwork->work))
+                return;
+
         while (!cancel_delayed_work(dwork))
                 flush_workqueue(wq);
 }