This one changes behaviour a bit. If we haven't been able to allocate
req before, it would post an completion event with -EAGAIN. Now it will
break imidiately without consuming sqe. So the user will see, that 0
sqes was submitted/consumed.

Is that ok or we need to do something about it? 

On 07/11/2019 01:00, Pavel Begunkov wrote:
> Let io_submit_sqes() to allocate io_kiocb before fetching an sqe.
> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  fs/io_uring.c | 25 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 6524898831e0..0289bb3cc697 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2551,30 +2551,23 @@ static int io_queue_link_head(struct io_ring_ctx *ctx, struct io_kiocb *req,
>  
>  #define SQE_VALID_FLAGS	(IOSQE_FIXED_FILE|IOSQE_IO_DRAIN|IOSQE_IO_LINK)
>  
> -static void io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
> -			  struct io_submit_state *state, struct io_kiocb **link)
> +static void io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
> +			  struct sqe_submit *s, struct io_submit_state *state,
> +			  struct io_kiocb **link)
>  {
>  	struct io_uring_sqe *sqe_copy;
> -	struct io_kiocb *req;
>  	int ret;
>  
>  	/* enforce forwards compatibility on users */
>  	if (unlikely(s->sqe->flags & ~SQE_VALID_FLAGS)) {
>  		ret = -EINVAL;
> -		goto err;
> -	}
> -
> -	req = io_get_req(ctx, state);
> -	if (unlikely(!req)) {
> -		ret = -EAGAIN;
> -		goto err;
> +		goto err_req;
>  	}
>  
>  	ret = io_req_set_file(ctx, s, state, req);
>  	if (unlikely(ret)) {
>  err_req:
>  		io_free_req(req, NULL);
> -err:
>  		io_cqring_add_event(ctx, s->sqe->user_data, ret);
>  		return;
>  	}
> @@ -2710,9 +2703,15 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
>  
>  	for (i = 0; i < nr; i++) {
>  		struct sqe_submit s;
> +		struct io_kiocb *req;
>  
> -		if (!io_get_sqring(ctx, &s))
> +		req = io_get_req(ctx, statep);
> +		if (unlikely(!req))
>  			break;
> +		if (!io_get_sqring(ctx, &s)) {
> +			__io_free_req(req);
> +			break;
> +		}
>  
>  		if (io_sqe_needs_user(s.sqe) && !*mm) {
>  			mm_fault = mm_fault || !mmget_not_zero(ctx->sqo_mm);
> @@ -2740,7 +2739,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr,
>  		s.in_async = async;
>  		s.needs_fixed_file = async;
>  		trace_io_uring_submit_sqe(ctx, s.sqe->user_data, true, async);
> -		io_submit_sqe(ctx, &s, statep, &link);
> +		io_submit_sqe(ctx, req, &s, statep, &link);
>  		submitted++;
>  
>  		/*
> 

-- 
Pavel Begunkov