Hi,

It seems that openat calls issued via io_uring ignore changes to
RLIMIT_NOFILE. Maybe a wrong limit is checked. A short reproducer is
attached, it sets RLIMIT_NOFILE to a very low value and the sync
openat() call fails with "Too many open files", but io_uring one
succeeds. The resulting FD is completely usable, I've tried writing to
it successfully.

To be clear, originally I've encountered another side of this problem:
we increase the limit in our code, and io_uring's openat started to
fail after a while under load, while the sync calls executed on a
thread pool were working as expected. It's just easier to demo with
small limit.

Kernel 5.6-rc2, 5.6-rc6.

Hope it's the right place to report an issue like this.

Thanks.

-- 
Dmitry