On 31/03/2021 10:01, Hao Xu wrote:
> Now that we have multishot poll requests, one sqe can emit multiple
> cqes. given below example:
> sqe0(multishot poll)-->sqe1-->sqe2(drain req)
> sqe2 is designed to issue after sqe0 and sqe1 completed, but since sqe0
> is a multishot poll request, sqe2 may be issued after sqe0's event
> triggered twice before sqe1 completed. This isn't what users leverage
> drain requests for.
> Here a simple solution is to ignore all multishot poll cqes, which means
> drain requests won't wait those request to be done.
>
> Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
> ---
> fs/io_uring.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 513096759445..cd6d44cf5940 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -455,6 +455,7 @@ struct io_ring_ctx {
> struct callback_head *exit_task_work;
>
> struct wait_queue_head hash_wait;
> + unsigned multishot_cqes;
>
> /* Keep this last, we don't need it for the fast path */
> struct work_struct exit_work;
> @@ -1181,8 +1182,8 @@ static bool req_need_defer(struct io_kiocb *req, u32 seq)
> if (unlikely(req->flags & REQ_F_IO_DRAIN)) {
> struct io_ring_ctx *ctx = req->ctx;
>
> - return seq != ctx->cached_cq_tail
> - + READ_ONCE(ctx->cached_cq_overflow);
> + return seq + ctx->multishot_cqes != ctx->cached_cq_tail
> + + READ_ONCE(ctx->cached_cq_overflow);
> }
>
> return false;
> @@ -4897,6 +4898,7 @@ static bool io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
> {
> struct io_ring_ctx *ctx = req->ctx;
> unsigned flags = IORING_CQE_F_MORE;
> + bool multishot_poll = !(req->poll.events & EPOLLONESHOT);
>
> if (!error && req->poll.canceled) {
> error = -ECANCELED;
> @@ -4911,6 +4913,9 @@ static bool io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
> req->poll.done = true;
> flags = 0;
> }
> + if (multishot_poll)
> + ctx->multishot_cqes++;
> +
We need to make sure we do that only for a non-final complete, i.e.
not killing request, otherwise it'll double account the last one.
E.g. is failed __io_cqring_fill_event() in io_poll_complete() fine?
Other places?
Btw, we can use some tests :)
> io_commit_cqring(ctx);
> return !(flags & IORING_CQE_F_MORE);
> }
>
--
Pavel Begunkov
