linux-kernel - [ 44/49] cfq: explicitly use 64bit divide operation for 64bit arguments

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Date:	Sun, 29 Sep 2013 12:27:18 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Anatol Pomozov <anatol.pomozov@...il.com>,
	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Jonghwan Choi <jhbird.choi@...il.com>
Subject: [ 44/49] cfq: explicitly use 64bit divide operation for 64bit arguments

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Anatol Pomozov <anatol.pomozov@...il.com>

commit f3cff25f05f2ac29b2ee355e611b0657482f6f1d upstream.

'samples' is 64bit operant, but do_div() second parameter is 32.
do_div silently truncates high 32 bits and calculated result
is invalid.

In case if low 32bit of 'samples' are zeros then do_div() produces
kernel crash.

Signed-off-by: Anatol Pomozov <anatol.pomozov@...il.com>
Acked-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Cc: Jonghwan Choi <jhbird.choi@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/cfq-iosched.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1803,7 +1803,7 @@ static u64 cfqg_prfill_avg_queue_size(st
 
 	if (samples) {
 		v = blkg_stat_read(&cfqg->stats.avg_queue_size_sum);
-		do_div(v, samples);
+		v = div64_u64(v, samples);
 	}
 	__blkg_prfill_u64(sf, pd, v);
 	return 0;


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