dm thin metadata: check if in fail_io mode when setting needs_check

mainline inclusion
from mainline-v5.3-rc1
commit 54fa16ee
category: bugfix
bugzilla: 18564
CVE: NA

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

Check if in fail_io mode at start of dm_pool_metadata_set_needs_check().
Otherwise dm_pool_metadata_set_needs_check()'s superblock_lock() can
crash in dm_bm_write_lock() while accessing the block manager object
that was previously destroyed as part of a failed
dm_pool_abort_metadata() that ultimately set fail_io to begin with.

Also, update DMERR() message to more accurately describe
superblock_lock() failure.

Cc: stable@vger.kernel.org
Reported-by: NZdenek Kabelac <zkabelac@redhat.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>

Conflicts:
	drivers/md/dm-thin-metadata.c
Signed-off-by: NZhangXiaoxu <zhangxiaoxu5@huawei.com>
Reviewed-by: NYi Zhang <yi.zhang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/md/dm-thin-metadata.c

@@ -2001,16 +2001,19 @@ int dm_pool_register_metadata_threshold(struct dm_pool_metadata *pmd,
 
 int dm_pool_metadata_set_needs_check(struct dm_pool_metadata *pmd)
 {
-	int r;
+	int r = -EINVAL;
 	struct dm_block *sblock;
 	struct thin_disk_superblock *disk_super;
 
 	down_write(&pmd->root_lock);
+	if (pmd->fail_io)
+		goto out;
+
 	pmd->flags |= THIN_METADATA_NEEDS_CHECK_FLAG;
 
 	r = superblock_lock(pmd, &sblock);
 	if (r) {
-		DMERR("couldn't read superblock");
+		DMERR("couldn't lock superblock");
 		goto out;
 	}