[PATCH 1/3] block: move freeing disk into queue's release handler

[Ming Lei <ming.lei@redhat.com>]

So far block_device(for disk), gendisk and request queue are supposed to
be killed at the same time, because we can retrieve request queue from both
block_device->bd_queue and gendisk->queue directly, meantime disk is
associated with request queue directly via q->disk. Also request queue's
refcnt is grabbed when allocating disk, and released in disk's release
handler.

Also we put request queue in disk_release() and clear queue->disk there.
Meantime disk can be released before running blk_cleanup_queue(). This
way isn't reliable:

- some block core code(blk-cgroup, io scheduler, ...) usually deals with
request queue only, and sometimes they need to retrieve disk info via q->disk,
but both io scheduler and blk-cgroup are shutdown in blk_release_queue()
actually, and q->disk can be cleared before releasing queue.

- q->disk is referred in fast io code path, such as io account code, but
q->disk can be cleared when queue is active since queue is still needed
for handling passthrough/private request after disk is deleted

Move freeing disk into queue's release handler, so that block_device(for
disk), gendisk and request queue can be removed at the same time basically,
then q->disk can be used reliably. This way is reasonable too, since
request queue becomes dying actually in del_gendisk(), see commit
8e141f9eb803 ("block: drain file system I/O on del_gendisk").

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-sysfs.c | 13 +++++++++++++
 block/genhd.c     |  7 +++++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e20eadfcf5c8..dc8af443b29b 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -12,6 +12,7 @@
 #include <linux/blk-mq.h>
 #include <linux/blk-cgroup.h>
 #include <linux/debugfs.h>
+#include <linux/fs.h>
 
 #include "blk.h"
 #include "blk-mq.h"
@@ -811,6 +812,18 @@ static void blk_release_queue(struct kobject *kobj)
 
 	bioset_exit(&q->bio_split);
 
+	/*
+	 * Free associated disk now if there is.
+	 *
+	 * Follows cases in which request queue hasn't disk:
+	 *
+	 * - not active LUN probed for scsi host
+	 *
+	 * - nvme's admin queue
+	 */
+	if (q->disk)
+		iput(q->disk->part0->bd_inode);
+
 	ida_simple_remove(&blk_queue_ida, q->id);
 	call_rcu(&q->rcu_head, blk_free_queue_rcu);
 }
diff --git a/block/genhd.c b/block/genhd.c
index 626c8406f21a..6357cab37eef 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1112,9 +1112,12 @@ static void disk_release(struct device *dev)
 	disk_release_events(disk);
 	kfree(disk->random);
 	xa_destroy(&disk->part_tbl);
-	disk->queue->disk = NULL;
+
+	/*
+	 * delay freeing disk/and its bdev into request queue's release
+	 * handler, then all can be killed at the same time
+	 */
 	blk_put_queue(disk->queue);
-	iput(disk->part0->bd_inode);	/* frees the disk */
 }
 
 static int block_uevent(struct device *dev, struct kobj_uevent_env *env)
-- 
2.31.1