This is a note to let you know that I've just added the patch titled
sched: Avoid prev->stime underflow
to the 3.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-avoid-prev-stime-underflow.patch
and it can be found in the queue-3.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 68aa8efcd1ab961e4684ef5af32f72a6ec1911de Mon Sep 17 00:00:00 2001
From: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
Date: Tue, 30 Apr 2013 11:35:06 +0200
Subject: sched: Avoid prev->stime underflow
From: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
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@xxxxxxxx>
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/1367314507-9728-3-git-send-email-sgruszka@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
Patches currently in stable-queue which might be from sgruszka@xxxxxxxxxx are
queue-3.9/sched-do-not-account-bogus-utime.patch
queue-3.9/revert-math64-new-div64_u64_rem-helper.patch
queue-3.9/sched-lower-chances-of-cputime-scaling-overflow.patch
queue-3.9/sched-avoid-prev-stime-underflow.patch
queue-3.9/sched-avoid-cputime-scaling-overflow.patch
queue-3.9/math64-new-div64_u64_rem-helper.patch
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