[ 3.8.y.z extended stable ] Patch "cfq: explicitly use 64bit divide operation for 64bit arguments" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.11.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From d6150c6fc36fa135f6b75aa04c54d83abd7a6bca Mon Sep 17 00:00:00 2001
From: Anatol Pomozov <anatol.pomozov at gmail.com>
Date: Sun, 22 Sep 2013 12:43:47 -0600
Subject: cfq: explicitly use 64bit divide operation for 64bit arguments

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 at gmail.com>
Acked-by: Tejun Heo <tj at kernel.org>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 block/cfq-iosched.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index e62e920..1a872282 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1484,7 +1484,7 @@ 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;
--
1.8.1.2