diff options
| author | Stanislaw Gruszka <sgruszka@redhat.com> | 2013-04-30 11:35:06 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-05-19 11:38:19 -0700 |
| commit | 6bc7f6efc8451170ce0b70f3f5e08202109e1702 (patch) | |
| tree | 71578492ecb3d1051b87965fa82081e5f79b8e7f /kernel | |
| parent | 859a8c0d7865dad5fa818f311ae984fbe5cd5483 (diff) | |
sched: Avoid prev->stime underflow
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@sr71.net>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: rostedt@goodmis.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1367314507-9728-3-git-send-email-sgruszka@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/cputime.c | 14 |
1 files changed, 7 insertions, 7 deletions
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 910d1f5be442..6af50adcc0ff 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -574,7 +574,7 @@ static void cputime_adjust(struct task_cputime *curr, 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_cputime *curr, 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_cputime *curr, * 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; |