From: Anatol Pomozov <anatol.pomozov@gmail.com>
Date: Sun, 22 Sep 2013 18:43:47 +0000 (-0600)
Subject: cfq: explicitly use 64bit divide operation for 64bit arguments
X-Git-Tag: v3.12-rc2~4^2
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f3cff25f05f2ac29b2ee355e611b0657482f6f1d;p=karo-tx-linux.git

cfq: explicitly use 64bit divide operation for 64bit arguments

'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>
---

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f0468e252ee4..51e06ea06a2e 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1803,7 +1803,7 @@ static u64 cfqg_prfill_avg_queue_size(struct seq_file *sf,
 
 	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;