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Commit 240f62c8 authored by Chris Mason's avatar Chris Mason Committed by root
Browse files

Btrfs: use RCU instead of a spinlock to protect the root node 



The pointer to the extent buffer for the root of each tree
is protected by a spinlock so that we can safely read the pointer
and take a reference on the extent buffer.

But now that the extent buffers are freed via RCU, we can safely
use rcu_read_lock instead.

Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent c0da7aa1

fs/btrfs/ctree.c

+8 −19
Original line number Diff line number Diff line
@@ -147,10 +147,11 @@ noinline void btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p) 
struct extent_buffer *btrfs_root_node(struct btrfs_root *root)

{

	struct extent_buffer *eb;

	spin_lock(&root->node_lock);

	eb = root->node;



	rcu_read_lock();

	eb = rcu_dereference(root->node);

	extent_buffer_get(eb);

	spin_unlock(&root->node_lock);

	rcu_read_unlock();

	return eb;

}
@@ -165,14 +166,8 @@ struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root) 
	while (1) {

		eb = btrfs_root_node(root);

		btrfs_tree_lock(eb);



		spin_lock(&root->node_lock);

		if (eb == root->node) {

			spin_unlock(&root->node_lock);

		if (eb == root->node)

			break;

		}

		spin_unlock(&root->node_lock);



		btrfs_tree_unlock(eb);

		free_extent_buffer(eb);

	}
@@ -458,10 +453,8 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans, 
		else

			parent_start = 0;



		spin_lock(&root->node_lock);

		root->node = cow;

		extent_buffer_get(cow);

		spin_unlock(&root->node_lock);

		rcu_assign_pointer(root->node, cow);



		btrfs_free_tree_block(trans, root, buf, parent_start,

				      last_ref);
@@ -930,9 +923,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans, 
			goto enospc;

		}



		spin_lock(&root->node_lock);

		root->node = child;

		spin_unlock(&root->node_lock);

		rcu_assign_pointer(root->node, child);



		add_root_to_dirty_list(root);

		btrfs_tree_unlock(child);
@@ -2007,10 +1998,8 @@ static noinline int insert_new_root(struct btrfs_trans_handle *trans, 


	btrfs_mark_buffer_dirty(c);



	spin_lock(&root->node_lock);

	old = root->node;

	root->node = c;

	spin_unlock(&root->node_lock);

	rcu_assign_pointer(root->node, c);



	/* the super has an extra ref to root->node */

	free_extent_buffer(old);