btrfs: zoned: reorder log node allocation on zoned filesystem

This is the 3/3 patch to enable tree-log on zoned filesystems.

The allocation order of nodes of "fs_info->log_root_tree" and nodes of
"root->log_root" is not the same as the writing order of them. So, the
writing causes unaligned write errors.

Reorder the allocation of them by delaying allocation of the root node of
"fs_info->log_root_tree," so that the node buffers can go out sequentially
to devices.

Cc: Filipe Manana <fdmanana@gmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -1298,16 +1298,18 @@ int btrfs_init_log_root_tree(struct btrfs_trans_handle *trans,
 			     struct btrfs_fs_info *fs_info)
 {
 	struct btrfs_root *log_root;
-	int ret;
 
 	log_root = alloc_log_tree(trans, fs_info);
 	if (IS_ERR(log_root))
 		return PTR_ERR(log_root);
 
-	ret = btrfs_alloc_log_tree_node(trans, log_root);
-	if (ret) {
-		btrfs_put_root(log_root);
-		return ret;
+	if (!btrfs_is_zoned(fs_info)) {
+		int ret = btrfs_alloc_log_tree_node(trans, log_root);
+
+		if (ret) {
+			btrfs_put_root(log_root);
+			return ret;
+		}
 	}
 
 	WARN_ON(fs_info->log_root_tree);

fs/btrfs/tree-log.c

@@ -3162,6 +3162,19 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 	list_add_tail(&root_log_ctx.list, &log_root_tree->log_ctxs[index2]);
 	root_log_ctx.log_transid = log_root_tree->log_transid;
 
+	if (btrfs_is_zoned(fs_info)) {
+		mutex_lock(&fs_info->tree_root->log_mutex);
+		if (!log_root_tree->node) {
+			ret = btrfs_alloc_log_tree_node(trans, log_root_tree);
+			if (ret) {
+				mutex_unlock(&fs_info->tree_log_mutex);
+				mutex_unlock(&log_root_tree->log_mutex);
+				goto out;
+			}
+		}
+		mutex_unlock(&fs_info->tree_root->log_mutex);
+	}
+
 	/*
 	 * Now we are safe to update the log_root_tree because we're under the
 	 * log_mutex, and we're a current writer so we're holding the commit
@@ -3320,12 +3333,14 @@ static void free_log_tree(struct btrfs_trans_handle *trans,
 		.process_func = process_one_buffer
 	};
 
-	ret = walk_log_tree(trans, log, &wc);
-	if (ret) {
-		if (trans)
-			btrfs_abort_transaction(trans, ret);
-		else
-			btrfs_handle_fs_error(log->fs_info, ret, NULL);
+	if (log->node) {
+		ret = walk_log_tree(trans, log, &wc);
+		if (ret) {
+			if (trans)
+				btrfs_abort_transaction(trans, ret);
+			else
+				btrfs_handle_fs_error(log->fs_info, ret, NULL);
+		}
 	}
 
 	clear_extent_bits(&log->dirty_log_pages, 0, (u64)-1,