From: Jens Axboe <axboe@fb.com>
Date: Fri, 19 Jun 2015 16:19:36 +0000 (-0600)
Subject: cfq-iosched: fix sysfs oops when attempting to read unconfigured weights
X-Git-Tag: omap-for-v4.2/fixes-rc1^2~120^2~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9470e4a693db;p=pandora-kernel.git

cfq-iosched: fix sysfs oops when attempting to read unconfigured weights

If none of the devices in the system are using CFQ, then attempting to
read:

/sys/fs/cgroup/blkio/blkio.leaf_weight

will results in a NULL dereference. Check for a valid cfq_group_data
struct before attempting to dereference it.

Reported-by: Andrey Wagin <avagin@gmail.com>
Fixes: e48453c3 ("block, cgroup: implement policy-specific per-blkcg data")
Signed-off-by: Jens Axboe <axboe@fb.com>
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