Several block drivers call alloc_disk() followed by put_disk() if
something fails before device_add_disk() is called without calling
blk_cleanup_queue(). Make sure that also for this scenario a request
queue is dissociated from the cgroup controller. This patch avoids
that loading the parport_pc, paride and pf drivers triggers the
following kernel crash:

BUG: KASAN: null-ptr-deref in pi_init+0x42e/0x580 [paride]
Read of size 4 at addr 0000000000000008 by task modprobe/744
Call Trace:
dump_stack+0x9a/0xeb
kasan_report+0x139/0x350
pi_init+0x42e/0x580 [paride]
pf_init+0x2bb/0x1000 [pf]
do_one_initcall+0x8e/0x405
do_init_module+0xd9/0x2f2
load_module+0x3ab4/0x4700
SYSC_finit_module+0x176/0x1a0
do_syscall_64+0xee/0x2b0
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Reported-by: Alexandru Moise <redacted>
Fixes: a063057d7c73 ("block: Fix a race between request queue removal and the block cgroup controller") # v4.17
Signed-off-by: Bart Van Assche <redacted>
Tested-by: Alexandru Moise <redacted>
Reviewed-by: Johannes Thumshirn <redacted>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <redacted>
Cc: Alexandru Moise <redacted>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: <redacted>
---
 block/blk-sysfs.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index ca1984ecbdeb..fcadea471779 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c

@@ -802,6 +802,21 @@ static void __blk_release_queue(struct work_struct *work)
 		blk_stat_remove_callback(q, q->poll_cb);
 	blk_stat_free_callback(q->poll_cb);
 
+	if (!blk_queue_dead(q)) {
+		/*
+		 * Last reference was dropped without having called
+		 * blk_cleanup_queue().
+		 */
+		WARN_ONCE(blk_queue_init_done(q),
+			  "request queue %p has been registered but blk_cleanup_queue() has not been called for that queue\n",
+			  q);
+		blk_exit_queue(q);
+	}
+
+	WARN(blkg_root_lookup(q),
+	     "request queue %p is being released but it has not yet been removed from the blkcg controller\n",
+	     q);
+
 	blk_free_queue_stats(q->stats);
 
 	blk_exit_rl(q, &q->root_rl);

-- 
2.18.0