block: prevent lockdep false positive warning about 'bd_mutex'

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ETAB
CVE: NA

--------------------------------

Patch ("block: fix that part scan is disabled in device_add_disk()")
confuse lockdep to produce following warning:

=====================================================
WARNING: possible circular locking dependency detected
4.18.0+ #2 Tainted: G                 ---------r-  -
------------------------------------------------------
syz-executor.0/4652 is trying to acquire lock:
00000000ad5f5a19 (&mddev->open_mutex){+.+.}, at: md_open+0x13a/0x260 home/install/linux-rh-3-10/drivers/md/md.c:7626

but task is already holding lock:
000000005c3a3fea (&bdev->bd_mutex){+.+.}, at: __blkdev_get+0x156/0x1490 home/install/linux-rh-3-10/fs/block_dev.c:1583

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&bdev->bd_mutex){+.+.}:
       __mutex_lock_common home/install/linux-rh-3-10/kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0x105/0x1270 home/install/linux-rh-3-10/kernel/locking/mutex.c:1072
       __blkdev_get+0x156/0x1490 home/install/linux-rh-3-10/fs/block_dev.c:1583
       blkdev_get+0x33c/0xac0 home/install/linux-rh-3-10/fs/block_dev.c:1735
       disk_init_partition home/install/linux-rh-3-10/block/blk-sysfs.c:972 [inline]
       blk_register_queue+0x5ed/0x6c0 home/install/linux-rh-3-10/block/blk-sysfs.c:1055
       __device_add_disk+0xab5/0xd70 home/install/linux-rh-3-10/block/genhd.c:729
       sd_probe_async+0x447/0x852 home/install/linux-rh-3-10/drivers/scsi/sd.c:3249
       async_run_entry_fn+0xe1/0x700 home/install/linux-rh-3-10/kernel/async.c:127
       process_one_work+0x9cf/0x1940 home/install/linux-rh-3-10/kernel/workqueue.c:2175
       worker_thread+0x91/0xc50 home/install/linux-rh-3-10/kernel/workqueue.c:2321
       kthread+0x33a/0x400 home/install/linux-rh-3-10/kernel/kthread.c:257
       ret_from_fork+0x3a/0x50 home/install/linux-rh-3-10/arch/x86/entry/entry_64.S:355

-> #1 (&q->sysfs_dir_lock){+.+.}:
       __mutex_lock_common home/install/linux-rh-3-10/kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0x105/0x1270 home/install/linux-rh-3-10/kernel/locking/mutex.c:1072
       blk_register_queue+0x143/0x6c0 home/install/linux-rh-3-10/block/blk-sysfs.c:1010
       __device_add_disk+0xab5/0xd70 home/install/linux-rh-3-10/block/genhd.c:729
       add_disk home/install/linux-rh-3-10/./include/linux/genhd.h:447 [inline]
       md_alloc+0xb06/0x10d0 home/install/linux-rh-3-10/drivers/md/md.c:5525
       md_probe+0x32/0x60 home/install/linux-rh-3-10/drivers/md/md.c:5554
       kobj_lookup+0x2d2/0x450 home/install/linux-rh-3-10/drivers/base/map.c:152
       get_gendisk+0x3b/0x360 home/install/linux-rh-3-10/block/genhd.c:860
       bdev_get_gendisk home/install/linux-rh-3-10/fs/block_dev.c:1181 [inline]
       __blkdev_get+0x3b6/0x1490 home/install/linux-rh-3-10/fs/block_dev.c:1578
       blkdev_get+0x33c/0xac0 home/install/linux-rh-3-10/fs/block_dev.c:1735
       blkdev_open+0x1c2/0x250 home/install/linux-rh-3-10/fs/block_dev.c:1923
       do_dentry_open+0x686/0xf50 home/install/linux-rh-3-10/fs/open.c:777
       do_last home/install/linux-rh-3-10/fs/namei.c:3449 [inline]
       path_openat+0x92f/0x28c0 home/install/linux-rh-3-10/fs/namei.c:3578
       do_filp_open+0x1aa/0x2b0 home/install/linux-rh-3-10/fs/namei.c:3613
       do_sys_open+0x307/0x490 home/install/linux-rh-3-10/fs/open.c:1075
       do_syscall_64+0xca/0x5c0 home/install/linux-rh-3-10/arch/x86/entry/common.c:298
       entry_SYSCALL_64_after_hwframe+0x6a/0xdf

-> #0 (&mddev->open_mutex){+.+.}:
       lock_acquire+0x10b/0x3a0 home/install/linux-rh-3-10/kernel/locking/lockdep.c:3868
       __mutex_lock_common home/install/linux-rh-3-10/kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0x105/0x1270 home/install/linux-rh-3-10/kernel/locking/mutex.c:1072
       md_open+0x13a/0x260 home/install/linux-rh-3-10/drivers/md/md.c:7626
       __blkdev_get+0x2dc/0x1490 home/install/linux-rh-3-10/fs/block_dev.c:1599
       blkdev_get+0x33c/0xac0 home/install/linux-rh-3-10/fs/block_dev.c:1735
       blkdev_open+0x1c2/0x250 home/install/linux-rh-3-10/fs/block_dev.c:1923
       do_dentry_open+0x686/0xf50 home/install/linux-rh-3-10/fs/open.c:777
       do_last home/install/linux-rh-3-10/fs/namei.c:3449 [inline]
       path_openat+0x92f/0x28c0 home/install/linux-rh-3-10/fs/namei.c:3578
       do_filp_open+0x1aa/0x2b0 home/install/linux-rh-3-10/fs/namei.c:3613
       do_sys_open+0x307/0x490 home/install/linux-rh-3-10/fs/open.c:1075
       do_syscall_64+0xca/0x5c0 home/install/linux-rh-3-10/arch/x86/entry/common.c:298
       entry_SYSCALL_64_after_hwframe+0x6a/0xdf

other info that might help us debug this:

Chain exists of:
  &mddev->open_mutex --> &q->sysfs_dir_lock --> &bdev->bd_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&bdev->bd_mutex);
                               lock(&q->sysfs_dir_lock);
                               lock(&bdev->bd_mutex);
  lock(&mddev->open_mutex);

 *** DEADLOCK ***

Since 'bd_mutex' and 'sysfs_dir_lock' is different is for each device,
deadlock between md_open() and sd_probe_async() is impossible. However,
lockdep is treating 'bd_mutex' and 'sysfs_dir_lock' from different devices
the same, and patch "block: fix that part scan is disabled in
device_add_disk()" is holding 'bd_mutex' inside 'sysfs_dir_lock',
which causes the false positive warning.

Fix the false positive warning by don't grab 'bd_mutex' inside
'sysfs_dir_lock'.
Signed-off-by: NYu Kuai <yukuai3@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

block/blk-sysfs.c

@@ -948,10 +948,17 @@ int blk_register_queue(struct gendisk *disk)
 	 * before it's registration is done.
 	 */
 	disk->flags |= GENHD_FL_UP;
-	disk_init_partition(disk);
 	ret = 0;
 unlock:
 	mutex_unlock(&q->sysfs_dir_lock);
+	/*
+	 * Init partitions after releasing 'sysfs_dir_lock', otherwise lockdep
+	 * will be confused because it will treat 'bd_mutex' from different
+	 * devices as the same lock.
+	 */
+	if (!ret)
+		disk_init_partition(disk);
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(blk_register_queue);