On Tue, May 21, 2019 at 05:30:27PM +0100, David Howells wrote:

Al Viro [off-list ref] wrote:

quoted

Umm...  That's going to be very painful if you dup2() something to MAX_INT and
then run that; roughly 2G iterations of bouncing ->file_lock up and down,
without anything that would yield CPU in process.

If anything, I would suggest something like

	fd = *start_fd;
	grab the lock
        fdt = files_fdtable(files);
more:
	look for the next eviction candidate in ->open_fds, starting at fd
	if there's none up to max_fd
		drop the lock
		return NULL
	*start_fd = fd + 1;
	if the fscker is really opened and not just reserved
		rcu_assign_pointer(fdt->fd[fd], NULL);
		__put_unused_fd(files, fd);
		drop the lock
		return the file we'd got
	if (unlikely(need_resched()))
		drop lock
		cond_resched();
		grab lock
		fdt = files_fdtable(files);
	goto more;

with the main loop being basically
	while ((file = pick_next(files, &start_fd, max_fd)) != NULL)
		filp_close(file, files);

If we can live with close_from(int first) rather than close_range(), then this
can perhaps be done a lot more efficiently by:

Yeah, you mentioned this before. I do like being able to specify an
upper bound to have the ability to place fds strategically after said
upper bound.
I have used this quite a few times where I know that given task may have
inherited up to m fds and I want to inherit a specific pipe who's fd I
know. Then I'd dup2(pipe_fd, <upper_bound + 1>) and then close all
other fds. Is that too much of a corner case?

Christian