btrfs: dev-replace: replace's scrub must not be running in suspended state

When the replace state is in the suspended state, btrfs_scrub_cancel()
should fail with -ENOTCONN as there is no scrub running. As a safety
catch check if btrfs_scrub_cancel() returns -ENOTCONN and assert if it
doesn't.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/dev-replace.c

@@ -840,7 +840,9 @@ int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info)
 
 		btrfs_dev_replace_write_unlock(dev_replace);
 
-		btrfs_scrub_cancel(fs_info);
+		/* Scrub for replace must not be running in suspended state */
+		ret = btrfs_scrub_cancel(fs_info);
+		ASSERT(ret != -ENOTCONN);
 
 		trans = btrfs_start_transaction(root, 0);
 		if (IS_ERR(trans)) {