commit 68aa8efcd1ab961e4684ef5af32f72a6ec1911de upstream. Dave Hansen reported strange utime/stime values on his system: https://lkml.org/lkml/2013/4/4/435
This happens because prev->stime value is bigger than rtime value. Root of the problem are non-monotonic rtime values (i.e. current rtime is smaller than previous rtime) and that should be debugged and fixed. But since problem did not manifest itself before commit 62188451f0d63add7ad0cd2a1ae269d600c1663d "cputime: Avoid multiplication overflow on utime scaling", it should be threated as regression, which we can easily fixed on cputime_adjust() function. For now, let's apply this fix, but further work is needed to fix root of the problem. Reported-and-tested-by: Dave Hansen <[email protected]> Signed-off-by: Stanislaw Gruszka <[email protected]> Cc: Frederic Weisbecker <[email protected]> Cc: [email protected] Cc: Linus Torvalds <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Peter Zijlstra <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- This patch (posed some time ago here: http://marc.info/?l=linux-kernel&m=136611036704038&w=2) was tested by Dave Hansen: http://marc.info/?l=linux-kernel&m=136614633018007&w=2 kernel/sched/cputime.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index e93cca9..a91cbb1 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -543,7 +543,7 @@ static void cputime_adjust(struct task_cputime *curr, struct cputime *prev, cputime_t *ut, cputime_t *st) { - cputime_t rtime, stime, total; + cputime_t rtime, stime, utime, total; stime = curr->stime; total = stime + curr->utime; @@ -560,10 +560,13 @@ static void cputime_adjust(struct task_cputime *curr, */ rtime = nsecs_to_cputime(curr->sum_exec_runtime); - if (total) + if (total) { stime = scale_stime(stime, rtime, total); - else + utime = rtime - stime; + } else { stime = rtime; + utime = 0; + } /* * If the tick based count grows faster than the scheduler one, @@ -571,7 +574,7 @@ static void cputime_adjust(struct task_cputime *curr, * Let's enforce monotonicity. */ prev->stime = max(prev->stime, stime); - prev->utime = max(prev->utime, rtime - prev->stime); + prev->utime = max(prev->utime, utime); *ut = prev->utime; *st = prev->stime; -- 1.7.11.7 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
