diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 07810891e20458..cc89b63d65a4df 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -2555,8 +2555,14 @@ static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root,
  * @p:		Holds all btree nodes along the search path
  * @root:	The root node of the tree
  * @key:	The key we are looking for
- * @ins_len:	Indicates purpose of search, for inserts it is 1, for
- *		deletions it's -1. 0 for plain searches
+ * @ins_len:	Indicates purpose of search:
+ *              >0  for inserts it's size of item inserted (*)
+ *              <0  for deletions
+ *               0  for plain searches, not modifying the tree
+ *
+ *              (*) If size of item inserted doesn't include
+ *              sizeof(struct btrfs_item), then p->search_for_extension must
+ *              be set.
  * @cow:	boolean should CoW operations be performed. Must always be 1
  *		when modifying the tree.
  *
@@ -2717,6 +2723,20 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 
 		if (level == 0) {
 			p->slots[level] = slot;
+			/*
+			 * Item key already exists. In this case, if we are
+			 * allowed to insert the item (for example, in dir_item
+			 * case, item key collision is allowed), it will be
+			 * merged with the original item. Only the item size
+			 * grows, no new btrfs item will be added. If
+			 * search_for_extension is not set, ins_len already
+			 * accounts the size btrfs_item, deduct it here so leaf
+			 * space check will be correct.
+			 */
+			if (ret == 0 && ins_len > 0 && !p->search_for_extension) {
+				ASSERT(ins_len >= sizeof(struct btrfs_item));
+				ins_len -= sizeof(struct btrfs_item);
+			}
 			if (ins_len > 0 &&
 			    btrfs_leaf_free_space(b) < ins_len) {
 				if (write_lock_level < 1) {
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2674f24cf2e003..3935d297d19818 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -368,6 +368,12 @@ struct btrfs_path {
 	unsigned int search_commit_root:1;
 	unsigned int need_commit_sem:1;
 	unsigned int skip_release_on_error:1;
+	/*
+	 * Indicate that new item (btrfs_search_slot) is extending already
+	 * existing item and ins_len contains only the data size and not item
+	 * header (ie. sizeof(struct btrfs_item) is not included).
+	 */
+	unsigned int search_for_extension:1;
 };
 #define BTRFS_MAX_EXTENT_ITEM_SIZE(r) ((BTRFS_LEAF_DATA_SIZE(r->fs_info) >> 4) - \
 					sizeof(struct btrfs_item))
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 56ea380f5a1788..d79b8369e6aafe 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -844,6 +844,7 @@ int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
 	want = extent_ref_type(parent, owner);
 	if (insert) {
 		extra_size = btrfs_extent_inline_ref_size(want);
+		path->search_for_extension = 1;
 		path->keep_locks = 1;
 	} else
 		extra_size = -1;
@@ -996,6 +997,7 @@ int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
 out:
 	if (insert) {
 		path->keep_locks = 0;
+		path->search_for_extension = 0;
 		btrfs_unlock_up_safe(path, 1);
 	}
 	return err;
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 1545c22ef2804c..6ccfc019ad909e 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -1016,8 +1016,10 @@ int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
 	}
 
 	btrfs_release_path(path);
+	path->search_for_extension = 1;
 	ret = btrfs_search_slot(trans, root, &file_key, path,
 				csum_size, 1);
+	path->search_for_extension = 0;
 	if (ret < 0)
 		goto out;