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

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Date:	Mon, 14 Dec 2015 15:47:23 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	<mingo@...hat.com>, <peterz@...radead.org>
CC:	<bsegall@...gle.com>, <dietmar.eggemann@....com>,
	<linux-kernel@...r.kernel.org>, <yuyang.du@...el.com>,
	<pjt@...gle.com>, <morten.rasmussen@....com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: [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@...tuozzo.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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