linux-kernel - [ 021/102] sched: Do not account bogus utime

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Message-Id: <20130517213246.613748873@linuxfoundation.org>
Date:	Fri, 17 May 2013 14:35:36 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Stanislaw Gruszka <sgruszka@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Hansen <dave@...1.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, rostedt@...dmis.org
Subject: [ 021/102] sched: Do not account bogus utime

3.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stanislaw Gruszka <sgruszka@...hat.com>

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@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: rostedt@...dmis.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Dave Hansen <dave@...1.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/1367314507-9728-2-git-send-email-sgruszka@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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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