In journal_init_dev(), if super bdev is used as 'j_dev_bd', then
blkdev_get_by_dev() is called with NULL holder, otherwise, holder will
be journal. However, later in release_journal_dev(), blkdev_put() is
called with journal unconditionally, cause following warning:

WARNING: CPU: 1 PID: 5034 at block/bdev.c:617 bd_end_claim block/bdev.c:617 [inline]
WARNING: CPU: 1 PID: 5034 at block/bdev.c:617 blkdev_put+0x562/0x8a0 block/bdev.c:901
RIP: 0010:blkdev_put+0x562/0x8a0 block/bdev.c:901
Call Trace:
 <TASK>
 release_journal_dev fs/reiserfs/journal.c:2592 [inline]
 free_journal_ram+0x421/0x5c0 fs/reiserfs/journal.c:1896
 do_journal_release fs/reiserfs/journal.c:1960 [inline]
 journal_release+0x276/0x630 fs/reiserfs/journal.c:1971
 reiserfs_put_super+0xe4/0x5c0 fs/reiserfs/super.c:616
 generic_shutdown_super+0x158/0x480 fs/super.c:499
 kill_block_super+0x64/0xb0 fs/super.c:1422
 deactivate_locked_super+0x98/0x160 fs/super.c:330
 deactivate_super+0xb1/0xd0 fs/super.c:361
 cleanup_mnt+0x2ae/0x3d0 fs/namespace.c:1247
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xadc/0x2a30 kernel/exit.c:874
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1024
 __do_sys_exit_group kernel/exit.c:1035 [inline]
 __se_sys_exit_group kernel/exit.c:1033 [inline]
 __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1033
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fix this problem by passing in NULL holder in this case.

Reported-by: syzbot+04625c80899f4555de39@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=04625c80899f4555de39
Fixes: 2736e8ee ("block: use the holder as indication for exclusive opens")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230620111322.1014775-1-yukuai1@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>