[PATCH] timers: consider slack value in mod_timer()

[Sebastian Andrzej Siewior <sebastian@breakpoint.cc>]

There is an optimization which does not update the timer if the timer
was pending and the expiration time was unchanged.
Since commit 3bbb9ec9 ("timers: Introduce the concept of timer slack for
legacy timers") this optimization is no longer applied for timers where
the expiration time got extended due to the slack value. So here it adds
the check again after the expiration time might have been updated.

Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
---
 kernel/timer.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/timer.c b/kernel/timer.c
index fd61986..bf09726 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -804,6 +804,8 @@ int mod_timer(struct timer_list *timer, unsigned long expires)
 		return 1;
 
 	expires = apply_slack(timer, expires);
+	if (timer_pending(timer) && timer->expires == expires)
+		return 1;
 
 	return __mod_timer(timer, expires, false, TIMER_NOT_PINNED);
 }
-- 
1.7.4.4