3 files changed, 59 insertions, 1 deletions

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 5bc7a0d325e7..2c726b7b9faa 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -367,6 +367,54 @@ out:
 }
 
 /**
+ * search_extent_mapping - find a nearby extent map
+ * @tree:	tree to lookup in
+ * @start:	byte offset to start the search
+ * @len:	length of the lookup range
+ *
+ * Find and return the first extent_map struct in @tree that intersects the
+ * [start, len] range.
+ *
+ * If one can't be found, any nearby extent may be returned
+ */
+struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
+					 u64 start, u64 len)
+{
+	struct extent_map *em;
+	struct rb_node *rb_node;
+	struct rb_node *prev = NULL;
+	struct rb_node *next = NULL;
+
+	rb_node = __tree_search(&tree->map, start, &prev, &next);
+	if (!rb_node && prev) {
+		em = rb_entry(prev, struct extent_map, rb_node);
+		goto found;
+	}
+	if (!rb_node && next) {
+		em = rb_entry(next, struct extent_map, rb_node);
+		goto found;
+	}
+	if (!rb_node) {
+		em = NULL;
+		goto out;
+	}
+	if (IS_ERR(rb_node)) {
+		em = ERR_PTR(PTR_ERR(rb_node));
+		goto out;
+	}
+	em = rb_entry(rb_node, struct extent_map, rb_node);
+	goto found;
+
+	em = NULL;
+	goto out;
+
+found:
+	atomic_inc(&em->refs);
+out:
+	return em;
+}
+
+/**
  * remove_extent_mapping - removes an extent_map from the extent tree
  * @tree:	extent tree to remove from
  * @em:		extent map beeing removed
diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index d3d442f4bbbd..ab6d74b6e647 100644
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -60,4 +60,6 @@ void free_extent_map(struct extent_map *em);
 int __init extent_map_init(void);
 void extent_map_exit(void);
 int unpin_extent_cache(struct extent_map_tree *tree, u64 start, u64 len);
+struct extent_map *search_extent_mapping(struct extent_map_tree *tree,
+					 u64 start, u64 len);
 #endif
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 941f1b71cd22..81ba6654c332 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -726,6 +726,15 @@ static noinline int cow_file_range(struct inode *inode,
 	BUG_ON(disk_num_bytes >
 	       btrfs_super_total_bytes(&root->fs_info->super_copy));
 
+
+	read_lock(&BTRFS_I(inode)->extent_tree.lock);
+	em = search_extent_mapping(&BTRFS_I(inode)->extent_tree,
+				   start, num_bytes);
+	if (em) {
+		alloc_hint = em->block_start;
+		free_extent_map(em);
+	}
+	read_unlock(&BTRFS_I(inode)->extent_tree.lock);
 	btrfs_drop_extent_cache(inode, start, start + num_bytes - 1, 0);
 
 	while (disk_num_bytes > 0) {
@@ -738,7 +747,6 @@ static noinline int cow_file_range(struct inode *inode,
 		em = alloc_extent_map(GFP_NOFS);
 		em->start = start;
 		em->orig_start = em->start;
-
 		ram_size = ins.offset;
 		em->len = ins.offset;