Re: [PATCH v2] io_uring: add support for multishot timeouts

[Pavel Begunkov <asml.silence@gmail.com>]

On 4/12/23 23:27, David Wei wrote:
> A multishot timeout submission will repeatedly generate completions with
> the IORING_CQE_F_MORE cflag set. Depending on the value of the `off' field
> in the submission, these timeouts can either repeat indefinitely until
> cancelled (`off' = 0) or for a fixed number of times (`off' > 0).
> 
> Only noseq timeouts (i.e. not dependent on the number of I/O
> completions) are supported.
> 
> An indefinite timer will be cancelled with EOVERFLOW if the CQ ever
> overflows.

Seems mostly fine, two comments below


> Signed-off-by: David Wei <davidhwei@meta.com>
> ---
>   include/uapi/linux/io_uring.h |  1 +
>   io_uring/timeout.c            | 59 +++++++++++++++++++++++++++++++++--
>   2 files changed, 57 insertions(+), 3 deletions(-)
> 
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index f8d14d1c58d3..0716cb17e436 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -250,6 +250,7 @@ enum io_uring_op {
>   #define IORING_TIMEOUT_REALTIME		(1U << 3)
>   #define IORING_LINK_TIMEOUT_UPDATE	(1U << 4)
>   #define IORING_TIMEOUT_ETIME_SUCCESS	(1U << 5)
> +#define IORING_TIMEOUT_MULTISHOT	(1U << 6)
>   #define IORING_TIMEOUT_CLOCK_MASK	(IORING_TIMEOUT_BOOTTIME | IORING_TIMEOUT_REALTIME)
>   #define IORING_TIMEOUT_UPDATE_MASK	(IORING_TIMEOUT_UPDATE | IORING_LINK_TIMEOUT_UPDATE)
>   /*
> diff --git a/io_uring/timeout.c b/io_uring/timeout.c
> index 5c6c6f720809..61b8488565ce 100644
...
> +static void io_timeout_complete(struct io_kiocb *req, struct io_tw_state *ts)
> +{
> +	struct io_timeout *timeout = io_kiocb_to_cmd(req, struct io_timeout);
> +	struct io_timeout_data *data = req->async_data;
> +	struct io_ring_ctx *ctx = req->ctx;
> +
> +	if (!io_timeout_finish(timeout, data)) {
> +		bool filled;
> +		filled = io_aux_cqe(ctx, false, req->cqe.user_data, -ETIME,
> +				      IORING_CQE_F_MORE, false);
> +		if (filled) {
> +			/* re-arm timer */
> +			spin_lock_irq(&ctx->timeout_lock);
> +			list_add(&timeout->list, ctx->timeout_list.prev);
> +			data->timer.function = io_timeout_fn;
> +			hrtimer_start(&data->timer, timespec64_to_ktime(data->ts), data->mode);
> +			spin_unlock_irq(&ctx->timeout_lock);
> +			return;
> +		}
> +		io_req_set_res(req, -EOVERFLOW, 0);

Let's not change the return value. It's considered a normal completion
and we don't change the code for them. And there is IORING_CQE_F_MORE
for userspace to figure out that it has been terminated.


> +	}
> +
> +	io_req_task_complete(req, ts);
> +}
> +
>   static bool io_kill_timeout(struct io_kiocb *req, int status)
>   	__must_hold(&req->ctx->timeout_lock)
>   {
> @@ -212,7 +253,7 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer)
>   		req_set_fail(req);
>   
>   	io_req_set_res(req, -ETIME, 0);
> -	req->io_task_work.func = io_req_task_complete;
> +	req->io_task_work.func = io_timeout_complete;
>   	io_req_task_work_add(req);
>   	return HRTIMER_NORESTART;
>   }
> @@ -470,16 +511,28 @@ static int __io_timeout_prep(struct io_kiocb *req,
>   		return -EINVAL;
>   	flags = READ_ONCE(sqe->timeout_flags);
>   	if (flags & ~(IORING_TIMEOUT_ABS | IORING_TIMEOUT_CLOCK_MASK |
> -		      IORING_TIMEOUT_ETIME_SUCCESS))
> +		      IORING_TIMEOUT_ETIME_SUCCESS |
> +		      IORING_TIMEOUT_MULTISHOT)) {
>   		return -EINVAL;
> +	}

Please, don't add braces, they're not needed here.

>   	/* more than one clock specified is invalid, obviously */
>   	if (hweight32(flags & IORING_TIMEOUT_CLOCK_MASK) > 1)
>   		return -EINVAL;
> +	/* multishot requests only make sense with rel values */
> +	if (!(~flags & (IORING_TIMEOUT_MULTISHOT | IORING_TIMEOUT_ABS)))
> +		return -EINVAL;
>   
>   	INIT_LIST_HEAD(&timeout->list);
>   	timeout->off = off;
>   	if (unlikely(off && !req->ctx->off_timeout_used))
>   		req->ctx->off_timeout_used = true;
> +	/*
> +	 * for multishot reqs w/ fixed nr of repeats, target_seq tracks the
> +	 * remaining nr
> +	 */
> +	timeout->repeats = 0;
> +	if ((flags & IORING_TIMEOUT_MULTISHOT) && off > 0)
> +		timeout->repeats = off;
>   
>   	if (WARN_ON_ONCE(req_has_async_data(req)))
>   		return -EFAULT;

-- 
Pavel Begunkov