releases/3.9.3/sched-do-not-account-bogus-utime.patch

   1 From 772c808a252594692972773f6ee41c289b8e0b2a Mon Sep 17 00:00:00 2001
   2 From: Stanislaw Gruszka <sgruszka@redhat.com>
   3 Date: Tue, 30 Apr 2013 11:35:05 +0200
   4 Subject: sched: Do not account bogus utime
   5
   6 From: Stanislaw Gruszka <sgruszka@redhat.com>
   7
   8 commit 772c808a252594692972773f6ee41c289b8e0b2a upstream.
   9
  10 Due to rounding in scale_stime(), for big numbers, scaled stime
  11 values will grow in chunks. Since rtime grow in jiffies and we
  12 calculate utime like below:
  13
  14         prev->stime = max(prev->stime, stime);
  15         prev->utime = max(prev->utime, rtime - prev->stime);
  16
  17 we could erroneously account stime values as utime. To prevent
  18 that only update prev->{u,s}time values when they are smaller
  19 than current rtime.
  20
  21 Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
  22 Cc: Frederic Weisbecker <fweisbec@gmail.com>
  23 Cc: rostedt@goodmis.org
  24 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  25 Cc: Dave Hansen <dave@sr71.net>
  26 Cc: Peter Zijlstra <peterz@infradead.org>
  27 Link: http://lkml.kernel.org/r/1367314507-9728-2-git-send-email-sgruszka@redhat.com
  28 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  29 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  30
  31 ---
  32  kernel/sched/cputime.c |    9 +++++++++
  33  1 file changed, 9 insertions(+)
  34
  35 --- a/kernel/sched/cputime.c
  36 +++ b/kernel/sched/cputime.c
  37 @@ -591,6 +591,14 @@ static void cputime_adjust(struct task_c
  38          */
  39         rtime = nsecs_to_cputime(curr->sum_exec_runtime);
  40
  41 +       /*
  42 +        * Update userspace visible utime/stime values only if actual execution
  43 +        * time is bigger than already exported. Note that can happen, that we
  44 +        * provided bigger values due to scaling inaccuracy on big numbers.
  45 +        */
  46 +       if (prev->stime + prev->utime >= rtime)
  47 +               goto out;
  48 +
  49         if (!rtime) {
  50                 stime = 0;
  51         } else if (!total) {
  52 @@ -608,6 +616,7 @@ static void cputime_adjust(struct task_c
  53         prev->stime = max(prev->stime, stime);
  54         prev->utime = max(prev->utime, rtime - prev->stime);
  55
  56 +out:
  57         *ut = prev->utime;
  58         *st = prev->stime;
  59  }