Commit-ID: 68aa8efcd1ab961e4684ef5af32f72a6ec1911de Gitweb: http://git.kernel.org/tip/68aa8efcd1ab961e4684ef5af32f72a6ec1911de Author: Stanislaw Gruszka <[email protected]> AuthorDate: Tue, 30 Apr 2013 11:35:06 +0200 Committer: Ingo Molnar <[email protected]> CommitDate: Tue, 30 Apr 2013 19:13:05 +0200
sched: Avoid prev->stime underflow 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]> Cc: <[email protected]> # 3.9+ 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]> --- kernel/sched/cputime.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 1b7c216..337a367 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -558,7 +558,7 @@ 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; if (vtime_accounting_enabled()) { *ut = curr->utime; @@ -589,13 +589,13 @@ static void cputime_adjust(struct task_cputime *curr, if (prev->stime + prev->utime >= rtime) goto out; - if (!rtime) { - stime = 0; - } else if (!total) { - stime = rtime; - } else { + if (total) { stime = scale_stime((__force u64)stime, (__force u64)rtime, (__force u64)total); + utime = rtime - stime; + } else { + stime = rtime; + utime = 0; } /* @@ -604,7 +604,7 @@ 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); out: *ut = prev->utime; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
