Re: [patch 2/3] kcmp: Add KCMP_EPOLL_TFD mode to compare epoll target files

On Mon, Mar 13, 2017 at 10:37:24AM -0700, Andrei Vagin wrote:

Here is one question inline.

Acked-by: Andrei Vagin <redacted>

Thanks!

quoted

+
+	files = get_files_struct(task2);
+	if (!files)
+		return -EBADF;
+
+	spin_lock(&files->file_lock);
+	filp_epoll = fcheck_files(files, slot.efd);
+	if (filp_epoll)
+		get_file(filp_epoll);
+	else
+		filp_tgt = ERR_PTR(-EBADF);
+	spin_unlock(&files->file_lock);
+	put_files_struct(files);

Why can we not use fget here ^^^^ ?

Because it's not @current's file table but foreigner process.
So we make sure there is no expand_fdtable in progress and
we test for file descriptor which is being freed.