https://github.com/torvalds/linux
Revision 7bdb59f1ad474bd7161adc8f923cdef10f2638d1 authored by Frederic Weisbecker on 07 February 2017, 16:44:54 UTC, committed by Thomas Gleixner on 10 February 2017, 08:43:48 UTC
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>
1 parent 3d88460
Tip revision: 7bdb59f1ad474bd7161adc8f923cdef10f2638d1 authored by Frederic Weisbecker on 07 February 2017, 16:44:54 UTC
tick/nohz: Fix possible missing clock reprog after tick soft restart
tick/nohz: Fix possible missing clock reprog after tick soft restart
Tip revision: 7bdb59f
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