Re: io_uring_setup spuriously returning ENOMEM for one user

[Pavel Begunkov <asml.silence@gmail.com>]

On 16/07/2020 23:05, Andres Freund wrote:
> Hi,
> 
> While testing the error handling of my uring using postgres branch I
> just encountered the situation that io_uring_setup() always fails with
> ENOMEN.
> 
> It only does so for the user I did the testing on and not for other
> users. During the testing a few io_uring using processes were kill -9'd
> and a few core-dumped after abort(). No io_uring using processes are
> still alive.
> 
> As the issue only happens to the one uid I suspect that
> current_user()->locked_mem got corrupted, perhaps after hitting the
> limit for real.

Any chance it's using SQPOLL mode?

> 
> Unfortunately I do not see any way to debug this without restarting. It
> seems the user wide limit isn't exported anywhere? I found
> uids_sysfs_init() while grepping around, but it seems that's just a
> leftover.
> 
> This happened on 07a56bb875afbe39dabbf6ba7b83783d166863db / 5.8rc5 +
> 16. I left the machine running for now, in case there's something that
> can be debugged while running. But I've to restart it in a bit. It took
> a while to hit this issue, unfortunately.
> 

-- 
Pavel Begunkov