commit 18d9be1a970c3704366df902b00871bea88d9f14 upstream.

Add a helper for queueing a request for async execution, in preparation
for optimizing it.

No functional change in this patch.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Reviewed-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>