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 <d...@sr71.net>
Cc: <sta...@vger.kernel.org> # 3.9+
Signed-off-by: Stanislaw Gruszka <sgrus...@redhat.com>
---
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 3f192bf..cc2dc3e 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;
--
1.7.11.7
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