io_uring: retry io_uring_submit() if it fails with errno=EINTR

io_uring: retry io_uring_submit() if it fails with errno=EINTR

As recently documented [1], io_uring_enter(2) syscall can return an
error (errno=EINTR) if the operation was interrupted by a delivery
of a signal before it could complete.

This should happen when IORING_ENTER_GETEVENTS flag is used, for
example during io_uring_submit_and_wait() or during io_uring_submit()
when IORING_SETUP_IOPOLL is enabled.

We shouldn't have this problem for now, but it's better to prevent it.

[1] https://github.com/axboe/liburing/commit/344355ec6619de8f4e64584c9736530b5346e4f4

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20200519133041.112138-1-sgarzare@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>