Messages in this thread Patch in this message | | | Subject | [PATCH] sched_clock: prevent scd->clock from moving backwards | From | Dave Kleikamp <> | Date | Wed, 08 Oct 2008 08:00:54 -0500 |
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sched_clock: prevent scd->clock from moving backwards
When sched_clock_cpu() couples the clocks between two cpus, it may increment scd->clock beyond the GTOD tick window that __update_sched_clock() uses to clamp the clock. A later call to __update_sched_clock() may move the clock back to scd->tick_gtod + TICK_NSEC, violating the clock's monotonic property.
This patch ensures that scd->clock will not be set backward.
Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index e8ab096..a989d64 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -118,13 +118,13 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now) /* * scd->clock = clamp(scd->tick_gtod + delta, - * max(scd->tick_gtod, scd->clock), - * scd->tick_gtod + TICK_NSEC); + * max(scd->tick_gtod, scd->clock), + * min(scd->clock, scd->tick_gtod + TICK_NSEC)); */ clock = scd->tick_gtod + delta; min_clock = wrap_max(scd->tick_gtod, scd->clock); - max_clock = scd->tick_gtod + TICK_NSEC; + max_clock = wrap_min(scd->clock, scd->tick_gtod + TICK_NSEC); clock = wrap_max(clock, min_clock); clock = wrap_min(clock, max_clock);
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