From 9470e4a693db84bee7becbba8de01af02bb23c9f Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@fb.com>
Date: Fri, 19 Jun 2015 10:19:36 -0600
Subject: [PATCH] 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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