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

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

[Stanislaw Gruszka]

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

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

[Peter Zijlstra]

On Tue, 2010-09-14 at 16:35 +0200, Stanislaw Gruszka wrote:
> 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.

Ah, right, (u64)foo * bar would have worked too I guess, but yeah, the
used (u64)(foo * bar) is wrong.

> 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>

Thanks, got it.

[tip:sched/urgent] sched: Fix user time incorrectly accounted as system time on 32-bit

[tip-bot for Stanislaw Gruszka]

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