btrfs: Always output error message when key/level verification fails

We have internal report of strange transaction abort due to EUCLEAN
without any error message.

Since error message inside verify_level_key() is only enabled for
CONFIG_BTRFS_DEBUG, the error message won't be printed on most builds.

This patch will make the error message mandatory, so when problem
happens we know what's causing the problem.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -404,12 +404,11 @@ int btrfs_verify_level_key(struct btrfs_fs_info *fs_info,
 
 	found_level = btrfs_header_level(eb);
 	if (found_level != level) {
-#ifdef CONFIG_BTRFS_DEBUG
-		WARN_ON(1);
+		WARN(IS_ENABLED(CONFIG_BTRFS_DEBUG),
+		     KERN_ERR "BTRFS: tree level check failed\n");
 		btrfs_err(fs_info,
 "tree level mismatch detected, bytenr=%llu level expected=%u has=%u",
 			  eb->start, level, found_level);
-#endif
 		return -EIO;
 	}
 
@@ -430,9 +429,9 @@ int btrfs_verify_level_key(struct btrfs_fs_info *fs_info,
 		btrfs_item_key_to_cpu(eb, &found_key, 0);
 	ret = btrfs_comp_cpu_keys(first_key, &found_key);
 
-#ifdef CONFIG_BTRFS_DEBUG
 	if (ret) {
-		WARN_ON(1);
+		WARN(IS_ENABLED(CONFIG_BTRFS_DEBUG),
+		     KERN_ERR "BTRFS: tree first key check failed\n");
 		btrfs_err(fs_info,
 "tree first key mismatch detected, bytenr=%llu parent_transid=%llu key expected=(%llu,%u,%llu) has=(%llu,%u,%llu)",
 			  eb->start, parent_transid, first_key->objectid,
@@ -440,7 +439,6 @@ int btrfs_verify_level_key(struct btrfs_fs_info *fs_info,
 			  found_key.objectid, found_key.type,
 			  found_key.offset);
 	}
-#endif
 	return ret;
 }