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authorFrederic Weisbecker <fweisbec@gmail.com>2017-02-07 17:44:54 +0100
committerThomas Gleixner <tglx@linutronix.de>2017-02-10 09:43:48 +0100
commit7bdb59f1ad474bd7161adc8f923cdef10f2638d1 (patch)
treea930c264e448fb7d89c14b29cb67bc8c4ba595e5
parent3d88460dbd285e7f32437b530d5bb7cb916142fa (diff)
tick/nohz: Fix possible missing clock reprog after tick soft restart
ts->next_tick keeps track of the next tick deadline in order to optimize clock programmation on irq exit and avoid redundant clock device writes. Now if ts->next_tick missed an update, we may spuriously miss a clock reprog later as the nohz code is fooled by an obsolete next_tick value. This is what happens here on a specific path: when we observe an expired timer from the nohz update code on irq exit, we perform a soft tick restart which simply fires the closest possible tick without actually exiting the nohz mode and restoring a periodic state. But we forget to update ts->next_tick accordingly. As a result, after the next tick resulting from such soft tick restart, the nohz code sees a stale value on ts->next_tick which doesn't match the clock deadline that just expired. If that obsolete ts->next_tick value happens to collide with the actual next tick deadline to be scheduled, we may spuriously bypass the clock reprogramming. In the worst case, the tick may never fire again. Fix this with a ts->next_tick reset on soft tick restart. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Reviewed: Wanpeng Li <wanpeng.li@hotmail.com> Acked-by: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1486485894-29173-1-git-send-email-fweisbec@gmail.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--kernel/time/tick-sched.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 74e0388cc88d..fc6f740d0277 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -725,6 +725,11 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
*/
if (delta == 0) {
tick_nohz_restart(ts, now);
+ /*
+ * Make sure next tick stop doesn't get fooled by past
+ * clock deadline
+ */
+ ts->next_tick = 0;
goto out;
}
}