[ 64/71] cfq: explicitly use 64bit divide operation for 64bit arguments

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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