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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
62188451f0 "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>
Cc: <stable@vger.kernel.org> # 3.9+
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>
hifive-unleashed-5.1
Stanislaw Gruszka 2013-04-30 11:35:06 +02:00 committed by Ingo Molnar
parent 772c808a25
commit 68aa8efcd1
1 changed files with 7 additions and 7 deletions
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14
kernel/sched/cputime.c
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@ -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;