block: Fix warning in bd_link_disk_holder()

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

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

Warning reports as follows:

 WARNING: CPU: 3 PID: 674 at fs/block_dev.c:1272 bd_link_disk_holder+0xcd/0x270
 Modules linked in: null_blk(+)
 CPU: 3 PID: 674 Comm: dmsetup Not tainted 5.10.0-16691-gf6076432827d-dirty #158
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-4
 RIP: 0010:bd_link_disk_holder+0xcd/0x270
 Code: 69 73 ee 00 44 89 e8 5b 48 83 05 c5 bf 6d 0c 01 5d 41 5c 41 5d 41 5e 41 8
 RSP: 0018:ffffc9000049bbb8 EFLAGS: 00010202
 RAX: ffff888104e39038 RBX: ffff888104185000 RCX: 0000000000000000
 RDX: 0000000000000001 RSI: ffffffffaa085692 RDI: 0000000000000000
 RBP: ffff88810cc2ae00 R08: ffffffffa853659b R09: 0000000000000000
 R10: ffffc9000049bbb0 R11: 720030626c6c756e R12: ffff88810e800000
 R13: ffff88810e800090 R14: ffff888103570c98 R15: ffff888103570c80
 FS:  00007fb49dc13dc0(0000) GS:ffff88813bd00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00007ff994ebde70 CR3: 000000010d54a000 CR4: 00000000000006e0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  dm_get_table_device+0x175/0x300
  dm_get_device+0x238/0x360
  linear_ctr+0xee/0x170
  dm_table_add_target+0x199/0x4b0
  table_load+0x18c/0x480
  ? table_clear+0x190/0x190
  ctl_ioctl+0x21d/0x640
  ? check_preemption_disabled+0x140/0x150
  dm_ctl_ioctl+0x12/0x20
  __se_sys_ioctl+0xb1/0x100
  __x64_sys_ioctl+0x1e/0x30
  do_syscall_64+0x45/0x70
  entry_SYSCALL_64_after_hwframe+0x44/0xa9

This can reproduce by concurrent operations:
	1. modprobe null_blk
	2. echo -e "0 10000 linear /dev/nullb0 0" > table
	   dmsetup create xxx table

t1: create disk a                   |     t2: dm setup
                                    |
device_add_disk                     |
 dev->devt = devt                   |
                        	    | dm_get_table_device
                        	    | open_table_device
                        	    | blkdev_get_by_dev -> succeed
				    | bd_link_disk_holder
                        	    |  -> holder_dir is still NULL
 register_disk -> create holder_dir
  kobject_create_and_add

device_add_disk() will set devt before creating holder_dir, which
leaves a window that dm_get_table_device() can find the disk by
devt while it's holder_dir is NULL.

So move GENHD_FL_UP in blk_register_queue() to avoid this warning and
fix a NULL-ptr in  __blk_mq_sched_bio_merge().
Signed-off-by: NLuo Meng <luomeng12@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
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

@@ -910,6 +910,12 @@ int blk_register_queue(struct gendisk *disk)
 		kobject_uevent(&q->elevator->kobj, KOBJ_ADD);
 	mutex_unlock(&q->sysfs_lock);
 
+
+	/*
+	 * Set the flag at last, so that block devcie can't be opened
+	 * before it's registration is done.
+	 */
+	disk->flags |= GENHD_FL_UP;
 	ret = 0;
 unlock:
 	mutex_unlock(&q->sysfs_dir_lock);

block/genhd.c

@@ -799,8 +799,6 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 	WARN_ON(!disk->minors &&
 		!(disk->flags & (GENHD_FL_EXT_DEVT | GENHD_FL_HIDDEN)));
 
-	disk->flags |= GENHD_FL_UP;
-
 	retval = blk_alloc_devt(&disk->part0, &devt);
 	if (retval) {
 		WARN_ON(1);