This is a note to let you know that I've just added the patch titled
sched: Do not account bogus utime
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-do-not-account-bogus-utime.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 <[email protected]> know about it.
>From 772c808a252594692972773f6ee41c289b8e0b2a Mon Sep 17 00:00:00 2001
From: Stanislaw Gruszka <[email protected]>
Date: Tue, 30 Apr 2013 11:35:05 +0200
Subject: sched: Do not account bogus utime
From: Stanislaw Gruszka <[email protected]>
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 <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: [email protected]
Cc: Linus Torvalds <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
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;
}
Patches currently in stable-queue which might be from [email protected] 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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