[PATCH v2] sched: fix user time incorrectly accounted as system time on 32 bit

[Stanislaw Gruszka <sgruszka@redhat.com>]

We have 32 bit variable overflow possibility when multiply in
task_times() and thread_group_times() functions. If overflow happens
calculated scaled utime value become wrongly small and scaled stime
wrongly 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>
Cc: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@kernel.org>  # 2.6.32.19+ (partially) and 2.6.33+
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
---
v1 -> v2
Fix mail recipients.

 kernel/sched.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 09b574e..eee9470 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3507,9 +3507,9 @@ 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
@@ -3540,9 +3540,9 @@ 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
-- 
1.7.1