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[PATCH v2] sched/fair: fix mul overflow on 32-bit systems

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  [PATCH v2] sched/fair: fix mul overflow on 32-bit systems Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-12-14 13:50 +0100
    Re: [PATCH v2] sched/fair: fix mul overflow on 32-bit systems Peter Zijlstra <peterz@infradead.org> - 2015-12-14 15:40 +0100

#1291159 — [PATCH v2] sched/fair: fix mul overflow on 32-bit systems

Make 'r' 64-bit type to avoid overflow in 'r * LOAD_AVG_MAX'
on 32-bit systems:
	UBSAN: Undefined behaviour in kernel/sched/fair.c:2785:18
	signed integer overflow:
	87950 * 47742 cannot be represented in type 'int'

Fixes: 9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking")
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 Changes since v1:
  - Removed wrong second hunk. Anyway, if fix for util_avg is needed,
    it deserves a separte patch.
    
 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 90e26b1..cfdc0e6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2689,7 +2689,7 @@ static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
 	int decayed, removed = 0;
 
 	if (atomic_long_read(&cfs_rq->removed_load_avg)) {
-		long r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
+		s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
 		sa->load_avg = max_t(long, sa->load_avg - r, 0);
 		sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
 		removed = 1;
-- 
2.4.10

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#1291231

On Mon, Dec 14, 2015 at 03:47:23PM +0300, Andrey Ryabinin wrote:
> Make 'r' 64-bit type to avoid overflow in 'r * LOAD_AVG_MAX'
> on 32-bit systems:
> 	UBSAN: Undefined behaviour in kernel/sched/fair.c:2785:18
> 	signed integer overflow:
> 	87950 * 47742 cannot be represented in type 'int'
> 
> Fixes: 9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking")
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

Thanks!
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