Commit-ID: 19d9f4225dd6a47fca430f15eeae345ceb95c301 Gitweb: http://git.kernel.org/tip/19d9f4225dd6a47fca430f15eeae345ceb95c301 Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Tue, 14 Apr 2015 21:09:25 +0000 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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 <tglx@xxxxxxxxxxxxx> Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> Link: http://lkml.kernel.org/r/20150414203503.580273114@xxxxxxxxxxxxx Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> --- 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-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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