Commit-ID: 19d9f4225dd6a47fca430f15eeae345ceb95c301 Gitweb: http://git.kernel.org/tip/19d9f4225dd6a47fca430f15eeae345ceb95c301 Author: Thomas Gleixner <[email protected]> AuthorDate: Tue, 14 Apr 2015 21:09:25 +0000 Committer: Thomas Gleixner <[email protected]> CommitDate: Wed, 22 Apr 2015 17:06:52 +0200
hrtimer: Avoid locking in hrtimer_cancel() if timer not active We can do a lockless check for hrtimer_active before actually taking the lock in hrtimer[_try_to]_cancel. This is useful for hotpath users like nanosleep as they avoid the lock dance when the timer has expired. This is safe because active is true when the timer is enqueued or the callback is running. Taking the hrtimer base lock does not protect against concurrent hrtimer_start calls, the callsite has to do the proper serialization itself. Signed-off-by: Thomas Gleixner <[email protected]> Acked-by: Peter Zijlstra <[email protected]> Cc: Preeti U Murthy <[email protected]> Cc: Viresh Kumar <[email protected]> Cc: Marcelo Tosatti <[email protected]> Cc: Frederic Weisbecker <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Thomas Gleixner <[email protected]> --- kernel/time/hrtimer.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index beab02d..3bac942 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -991,6 +991,15 @@ int hrtimer_try_to_cancel(struct hrtimer *timer) unsigned long flags; int ret = -1; + /* + * Check lockless first. If the timer is not active (neither + * enqueued nor running the callback, nothing to do here. The + * base lock does not serialize against a concurrent enqueue, + * so we can avoid taking it. + */ + if (!hrtimer_active(timer)) + return 0; + base = lock_hrtimer_base(timer, &flags); if (!hrtimer_callback_running(timer)) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
