Commit 6f8191fdf41d ("block: simplify disk shutdown") removed the call
to blk_get_queue() during gendisk allocation but missed to remove the
corresponding cleanup code blk_put_queue() for it. Thus, if the gendisk
allocation fails, the request_queue refcount gets decremented and
reaches 0, causing blk_mq_release() to be called with a hctx still
alive. That triggers a WARNING report, as found by syzkaller:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 23016 at block/blk-mq.c:3881
blk_mq_release+0xf8/0x3e0 block/blk-mq.c:3881
[...] stripped
RIP: 0010:blk_mq_release+0xf8/0x3e0 block/blk-mq.c:3881
[...] stripped
Call Trace:
 <TASK>
 blk_release_queue+0x153/0x270 block/blk-sysfs.c:780
 kobject_cleanup lib/kobject.c:673 [inline]
 kobject_release lib/kobject.c:704 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1c8/0x540 lib/kobject.c:721
 __alloc_disk_node+0x4f7/0x610 block/genhd.c:1388
 __blk_mq_alloc_disk+0x13b/0x1f0 block/blk-mq.c:3961
 loop_add+0x3e2/0xaf0 drivers/block/loop.c:1978
 loop_control_ioctl+0x133/0x620 drivers/block/loop.c:2150
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
[...] stripped

Fixes: 6f8191fdf41d ("block: simplify disk shutdown")
Reported-by: syzbot+31c9594f6e43b9289b25@syzkaller.appspotmail.com
Suggested-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Rafael Mendonca <rafaelmendsr@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220811232338.254673-1-rafaelmendsr@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>