ublk: honor IO_URING_F_NONBLOCK for handling control command

[ Upstream commit fa8e442e ]

Most of control command handlers may sleep, so return -EAGAIN in case
of IO_URING_F_NONBLOCK to defer the handling into io wq context.

Fixes: 71f28f31 ("ublk_drv: add io_uring based userspace block driver")
Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230104133235.836536-1-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>