[PATCH -next] block: fix blktrace debugfs entries leak

[Yu Kuai]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

Commit 99d055b4fd4b ("block: remove per-disk debugfs files in
blk_unregister_queue") moves blk_trace_shutdown() from
blk_release_queue() to blk_unregister_queue(), this is safe if blktrace
is created through sysfs, however, there are some regression in corner
cases:

1) for scsi, passthrough io can still be issued after del_gendisk, and
   blktrace debugfs entries will be removed immediately after
   del_gendisk(), therefor passthrough io can't be tracked and blktrace
   will complain:

   failed read of /sys/kernel/debug/block/sdb/trace0: 5/Input/output error

2) blktrace can still be enabled after del_gendisk() through ioctl if the
   disk is opened before del_gendisk(), and if blktrace is not shutdown
   through ioctl before closing the disk, debugfs entries will be
   leaked.

It seems 1) is not important, while 2) needs to be fixed apparently.

Fix this problem by shutdown blktrace in blk_free_queue(),
disk_release() is not used because scsi sg support blktrace without
gendisk, and this is safe because queue is not freed yet, and
blk_trace_shutdown() is reentrant.

Fixes: 99d055b4fd4b ("block: remove per-disk debugfs files in blk_unregister_queue")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/blk-core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 00c74330fa92..a0c949533a5d 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -263,6 +263,10 @@ static void blk_free_queue_rcu(struct rcu_head *rcu_head)
 
 static void blk_free_queue(struct request_queue *q)
 {
+	mutex_lock(&q->debugfs_mutex);
+	blk_trace_shutdown(q);
+	mutex_unlock(&q->debugfs_mutex);
+
 	blk_free_queue_stats(q->stats);
 	if (queue_is_mq(q))
 		blk_mq_release(q);
-- 
2.39.2