[PATCH] sched: fair: avoid integer overflow

[PATCH] sched: fair: avoid integer overflow

[Michal Nazarewicz]

From: Michal Nazarewicz <mina86@mina86.com>

sa->runnable_avg_sum is of type u32 but after shifting it by NICE_0_SHIFT
bits it is promoted to u64.  This of course makes no sense, since the
result will never be more then 32-bit long.  Casting sa->runnable_avg_sum
to u64 before it is shifted, fixes this problem.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index df77c60..50f1e170 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2153,7 +2153,7 @@ static inline void __update_tg_runnable_avg(struct sched_avg *sa,
 	long contrib;
 
 	/* The fraction of a cpu used by this cfs_rq */
-	contrib = div_u64(sa->runnable_avg_sum << NICE_0_SHIFT,
+	contrib = div_u64((u64)sa->runnable_avg_sum << NICE_0_SHIFT,
 			  sa->runnable_avg_period + 1);
 	contrib -= cfs_rq->tg_runnable_contrib;
 
-- 
1.8.3.2

Re: [PATCH] sched: fair: avoid integer overflow

[bsegall]

Michal Nazarewicz <mpn@google.com> writes:

> From: Michal Nazarewicz <mina86@mina86.com>
>
> sa->runnable_avg_sum is of type u32 but after shifting it by NICE_0_SHIFT
> bits it is promoted to u64.  This of course makes no sense, since the
> result will never be more then 32-bit long.  Casting sa->runnable_avg_sum
> to u64 before it is shifted, fixes this problem.
>
> Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Reviewed-by: Ben Segall <bsegall@google.com>

> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index df77c60..50f1e170 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2153,7 +2153,7 @@ static inline void __update_tg_runnable_avg(struct sched_avg *sa,
>  	long contrib;
>  
>  	/* The fraction of a cpu used by this cfs_rq */
> -	contrib = div_u64(sa->runnable_avg_sum << NICE_0_SHIFT,
> +	contrib = div_u64((u64)sa->runnable_avg_sum << NICE_0_SHIFT,
>  			  sa->runnable_avg_period + 1);
>  	contrib -= cfs_rq->tg_runnable_contrib;

[tip:sched/urgent] sched/fair: Avoid integer overflow

[tip-bot for Michal Nazarewicz]

Commit-ID:  85b088e934b9943322bfe37077289ae60f1b3414
Gitweb:     http://git.kernel.org/tip/85b088e934b9943322bfe37077289ae60f1b3414
Author:     Michal Nazarewicz <mina86@mina86.com>
AuthorDate: Sun, 10 Nov 2013 20:42:01 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Nov 2013 13:33:55 +0100

sched/fair: Avoid integer overflow

sa->runnable_avg_sum is of type u32 but after shifting it by NICE_0_SHIFT
bits it is promoted to u64.  This of course makes no sense, since the
result will never be more then 32-bit long.  Casting sa->runnable_avg_sum
to u64 before it is shifted, fixes this problem.

Reviewed-by: Ben Segall <bsegall@google.com>
Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1384112521-25177-1-git-send-email-mpn@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 201be78..e8b652e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2178,7 +2178,7 @@ static inline void __update_tg_runnable_avg(struct sched_avg *sa,
 	long contrib;
 
 	/* The fraction of a cpu used by this cfs_rq */
-	contrib = div_u64(sa->runnable_avg_sum << NICE_0_SHIFT,
+	contrib = div_u64((u64)sa->runnable_avg_sum << NICE_0_SHIFT,
 			  sa->runnable_avg_period + 1);
 	contrib -= cfs_rq->tg_runnable_contrib;