3.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
commit 772c808a252594692972773f6ee41c289b8e0b2a upstream.
Due to rounding in scale_stime(), for big numbers, scaled stime
values will grow in chunks. Since rtime grow in jiffies and we
calculate utime like below:
prev->stime = max(prev->stime, stime);
prev->utime = max(prev->utime, rtime - prev->stime);
we could erroneously account stime values as utime. To prevent
that only update prev->{u,s}time values when they are smaller
than current rtime.
Signed-off-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: rostedt@xxxxxxxxxxx
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1367314507-9728-2-git-send-email-sgruszka@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/cputime.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -591,6 +591,14 @@ static void cputime_adjust(struct task_c
*/
rtime = nsecs_to_cputime(curr->sum_exec_runtime);
+ /*
+ * Update userspace visible utime/stime values only if actual execution
+ * time is bigger than already exported. Note that can happen, that we
+ * provided bigger values due to scaling inaccuracy on big numbers.
+ */
+ if (prev->stime + prev->utime >= rtime)
+ goto out;
+
if (!rtime) {
stime = 0;
} else if (!total) {
@@ -608,6 +616,7 @@ static void cputime_adjust(struct task_c
prev->stime = max(prev->stime, stime);
prev->utime = max(prev->utime, rtime - prev->stime);
+out:
*ut = prev->utime;
*st = prev->stime;
}
--
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