btrfs: free path at can_nocow_extent() before checking for checksum items

When we look for checksum items, through csum_exist_in_range(), at
can_nocow_extent(), we no longer need the path that we have previously
allocated. Through csum_exist_in_range() -> btrfs_lookup_csums_range(),
we also end up allocating a path, so we are adding unnecessary extra
memory usage. So free the path before calling csum_exist_in_range().
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/inode.c

@@ -7229,6 +7229,14 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
 		goto out;
 	}
 
+	/*
+	 * We don't need the path anymore, plus through the csum_exist_in_range()
+	 * call below we will end up allocating another path. So free the path
+	 * to avoid unnecessary extra memory usage.
+	 */
+	btrfs_free_path(path);
+	path = NULL;
+
 	/*
 	 * adjust disk_bytenr and num_bytes to cover just the bytes
 	 * in this extent we are about to write.  If there