btrfs: stop allocating a path when checking if cross reference exists

At btrfs_cross_ref_exist() we always allocate a path, but we really don't
need to because all its callers (only 2) already have an allocated path
that is not being used when they call btrfs_cross_ref_exist(). So change
btrfs_cross_ref_exist() to take a path as an argument and update both
its callers to pass in the unused path they have when they call
btrfs_cross_ref_exist().

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -2784,7 +2784,8 @@ int btrfs_pin_extent_for_log_replay(struct btrfs_trans_handle *trans,
 				    u64 bytenr, u64 num_bytes);
 int btrfs_exclude_logged_extents(struct extent_buffer *eb);
 int btrfs_cross_ref_exist(struct btrfs_root *root,
-			  u64 objectid, u64 offset, u64 bytenr, bool strict);
+			  u64 objectid, u64 offset, u64 bytenr, bool strict,
+			  struct btrfs_path *path);
 struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
 					     struct btrfs_root *root,
 					     u64 parent, u64 root_objectid,

fs/btrfs/extent-tree.c

@@ -2357,15 +2357,10 @@ out:
 }
 
 int btrfs_cross_ref_exist(struct btrfs_root *root, u64 objectid, u64 offset,
-			  u64 bytenr, bool strict)
+			  u64 bytenr, bool strict, struct btrfs_path *path)
 {
-	struct btrfs_path *path;
 	int ret;
 
-	path = btrfs_alloc_path();
-	if (!path)
-		return -ENOMEM;
-
 	do {
 		ret = check_committed_ref(root, path, objectid,
 					  offset, bytenr, strict);
@@ -2376,7 +2371,7 @@ int btrfs_cross_ref_exist(struct btrfs_root *root, u64 objectid, u64 offset,
 	} while (ret == -EAGAIN);
 
 out:
-	btrfs_free_path(path);
+	btrfs_release_path(path);
 	if (btrfs_is_data_reloc_root(root))
 		WARN_ON(ret > 0);
 	return ret;

fs/btrfs/inode.c

@@ -1788,7 +1788,8 @@ next_slot:
 
 			ret = btrfs_cross_ref_exist(root, ino,
 						    found_key.offset -
-						    extent_offset, disk_bytenr, false);
+						    extent_offset, disk_bytenr,
+						    false, path);
 			if (ret) {
 				/*
 				 * ret could be -EIO if the above fails to read
@@ -7222,7 +7223,7 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
 
 	ret = btrfs_cross_ref_exist(root, btrfs_ino(BTRFS_I(inode)),
 				    key.offset - backref_offset, disk_bytenr,
-				    strict);
+				    strict, path);
 	if (ret) {
 		ret = 0;
 		goto out;