Re: [PATCH 13/18] io_uring: add file set registration

On 2/6/19 9:05 PM, Al Viro wrote:

On Wed, Feb 06, 2019 at 10:56:41AM -0700, Jens Axboe wrote:

quoted

On 2/5/19 6:01 PM, Al Viro wrote:

quoted

On Tue, Feb 05, 2019 at 05:27:29PM -0700, Jens Axboe wrote:

quoted

This should be better, passes some basic testing, too:

http://git.kernel.dk/cgit/linux-block/commit/?h=io_uring&id=01a93aa784319a02ccfa6523371b93401c9e0073

Verified that we're grabbing the right refs, and don't hold any
ourselves. For the file registration, forbid registration of the
io_uring fd, as that is pointless and will introduce a loop regardless
of fd passing.

*shrug*

So pass it to AF_UNIX socket and register _that_ - does't change the
underlying problem.

Maybe I'm being dense here, but it's an f_op match. Should catch a
passed fd as well, correct?

f_op match on _what_?

quoted

With that, how can there be a loop?

	io_uring_fd = ....
	socketpair(PF_UNIX, SOCK_STREAM, 0, sock_fds);
	register sock_fds[0] and sock_fds[1] to io_uring_fd
	send SCM_RIGHTS datagram with io_uring_fd to sock_fds[0]
	close sock_fds[0], sock_fds[1] and io_uring_fd

And there's your unreachable loop.

I created a small app to do just that, and ran it and verified that
->release() is called and the io_uring is released as expected. This
is run on the current -git branch, which has a socket backing for
the io_uring fd itself, but not for the registered files.

What am I missing here? Attaching the program as a reference.

-- 
Jens Axboe