Don't reinit io_ring_exit_work()'s exit work/completions on each
iteration, that's wasteful. Also add list_rotate_left(), so if we failed
to complete the task job, we don't try it again and again but defer it
until others are processed.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>