From: Dave Kleikamp Date: Thu, 9 Oct 2008 18:21:30 +0000 (-0500) Subject: sched_clock: prevent scd->clock from moving backwards X-Git-Tag: v2.6.28-rc1~267^2^2 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=5b7dba4ff834259a5623e03a565748704a8fe449;p=linux-2.6-omap-h63xx.git 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 Acked-by: Peter Zijlstra Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index e8ab096ddfe..81787248b60 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), + * max(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_max(scd->clock, scd->tick_gtod + TICK_NSEC); clock = wrap_max(clock, min_clock); clock = wrap_min(clock, max_clock);