Re: [PATCH 1/2] io_uring: make the logic clearer for io_sequence_defer

[yangerkun <yangerkun@huawei.com>]

On 2019/10/9 9:19, Jackie Liu wrote:
> __io_get_deferred_req is used to get all defer lists, including defer_list
> and timeout_list, but io_sequence_defer should be only cares about the sequence.
> 
> Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
> ---
>   fs/io_uring.c | 13 +++++--------
>   1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 8a0381f1a43b..8ec2443eb019 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -418,9 +418,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
>   static inline bool io_sequence_defer(struct io_ring_ctx *ctx,
>   				     struct io_kiocb *req)
>   {
> -	/* timeout requests always honor sequence */
> -	if (!(req->flags & REQ_F_TIMEOUT) &&
> -	    (req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) != REQ_F_IO_DRAIN)
> +	if ((req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) != REQ_F_IO_DRAIN)
>   		return false;
>   
>   	return req->sequence != ctx->cached_cq_tail + ctx->rings->sq_dropped;
> @@ -435,12 +433,11 @@ static struct io_kiocb *__io_get_deferred_req(struct io_ring_ctx *ctx,
>   		return NULL;
>   
>   	req = list_first_entry(list, struct io_kiocb, list);
> -	if (!io_sequence_defer(ctx, req)) {
> -		list_del_init(&req->list);
> -		return req;
> -	}
> +	if (!(req->flags & REQ_F_TIMEOUT) && io_sequence_defer(ctx, req))
> +		return NULL;
Hi,

For timeout req, we should also compare the sequence to determine to 
return NULL or the req. But now we will return req directly. Actually, 
no need to compare req->flags with REQ_F_TIMEOUT.

Another problem, before this change, a timeout req can also drain the 
sqe(io_queue_sqe->io_req_defer and add to refer list), i am not sure is 
it a right or wrong logic, but your patch fix that.

Thanks,
Kun.
>   
> -	return NULL;
> +	list_del_init(&req->list);
> +	return req;
>   }
>   
>   static struct io_kiocb *io_get_deferred_req(struct io_ring_ctx *ctx)
>