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: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 73e5300..8680110 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -147,10 +147,11 @@
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 @@
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 @@
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 @@
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 @@
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);