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Subject[tip:sched/urgent] sched: Fix user time incorrectly accounted as system time on 32-bit
Commit-ID:  e75e863dd5c7d96b91ebbd241da5328fc38a78cc
Gitweb: http://git.kernel.org/tip/e75e863dd5c7d96b91ebbd241da5328fc38a78cc
Author: Stanislaw Gruszka <sgruszka@redhat.com>
AuthorDate: Tue, 14 Sep 2010 16:35:14 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 15 Sep 2010 10:41:36 +0200

sched: Fix user time incorrectly accounted as system time on 32-bit

We have 32-bit variable overflow possibility when multiply in
task_times() and thread_group_times() functions. When the
overflow happens then the scaled utime value becomes erroneously
small and the scaled stime becomes i erroneously big.

Reported here:

https://bugzilla.redhat.com/show_bug.cgi?id=633037
https://bugzilla.kernel.org/show_bug.cgi?id=16559

Reported-by: Michael Chapman <redhat-bugzilla@very.puzzling.org>
Reported-by: Ciriaco Garcia de Celis <sysman@etherpilot.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: <stable@kernel.org> # 2.6.32.19+ (partially) and 2.6.33+
LKML-Reference: <20100914143513.GB8415@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index ed09d4f..dc85ceb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3513,9 +3513,9 @@ void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
rtime = nsecs_to_cputime(p->se.sum_exec_runtime);

if (total) {
- u64 temp;
+ u64 temp = rtime;

- temp = (u64)(rtime * utime);
+ temp *= utime;
do_div(temp, total);
utime = (cputime_t)temp;
} else
@@ -3546,9 +3546,9 @@ void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
rtime = nsecs_to_cputime(cputime.sum_exec_runtime);

if (total) {
- u64 temp;
+ u64 temp = rtime;

- temp = (u64)(rtime * cputime.utime);
+ temp *= cputime.utime;
do_div(temp, total);
utime = (cputime_t)temp;
} else

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