Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [ 023/102] sched: Avoid prev->stime underflow | Date | Fri, 17 May 2013 14:35:38 -0700 |
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3.9-stable review patch. If anyone has any objections, please let me know.
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From: Stanislaw Gruszka <sgruszka@redhat.com>
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 <dave@sr71.net> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: rostedt@goodmis.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Dave Hansen <dave@sr71.net> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1367314507-9728-3-git-send-email-sgruszka@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- kernel/sched/cputime.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)
--- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -574,7 +574,7 @@ static void cputime_adjust(struct task_c 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; @@ -599,13 +599,13 @@ static void cputime_adjust(struct task_c 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; } /* @@ -614,7 +614,7 @@ static void cputime_adjust(struct task_c * 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;
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