linux-kernel - [PATCH] sched: fair group: fix divide by zero

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Date:	Wed, 11 Jun 2008 15:12:05 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	mingo@...e.hu
CC:	peterz@...radead.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] sched: fair group: fix divide by zero

I found a bug which can be reproduced by this way:(linux-2.6.26-rc5, x86-64)
(use 2^32, 2^33, ...., 2^63 as shares value)

# mkdir /dev/cpuctl
# mount -t cgroup -o cpu cpuctl /dev/cpuctl
# cd /dev/cpuctl
# mkdir sub
# echo 0x8000000000000000 > sub/cpu.shares
# echo $$ > sub/tasks
oops here! divide by zero.

This is because do_div() expects the 2th parameter to be 32 bits,
but unsigned long is 64 bits in x86_64.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 08ae848..d3005b4 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -368,7 +368,7 @@ static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
 		cfs_rq = cfs_rq_of(se);
 
 		slice *= se->load.weight;
-		do_div(slice, cfs_rq->load.weight);
+		slice = div64_u64(slice, cfs_rq->load.weight);
 	}
 
 
@@ -399,7 +399,7 @@ static u64 sched_vslice_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
 			weight += se->load.weight;
 
 		vslice *= NICE_0_LOAD;
-		do_div(vslice, weight);
+		vslice = div64_u64(vslice, weight);
 	}
 
 	return vslice;


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