Re: [PATCH 1/8] io_uring: fix io_fail_links() locking

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

On 30/06/2020 17:38, Jens Axboe wrote:
> On 6/30/20 6:20 AM, Pavel Begunkov wrote:
>> 86b71d0daee05 ("io_uring: deduplicate freeing linked timeouts")
>> actually fixed one bug, where io_fail_links() doesn't consider
>> REQ_F_COMP_LOCKED, but added another -- io_cqring_fill_event()
>> without any locking
>>
>> Return locking back there and do it right with REQ_F_COMP_LOCKED
>> check.
> 
> Something like the below is much better, and it also makes it so that
> the static analyzers don't throw a fit. I'm going to fold this into
> the original.

Good point about analyzers, even uninitialised flags there is a warning.
This pattern usually prevents inlining, but don't care about
io_fail_links().

> 
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index e1410ff31892..a0aea78162a6 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1600,7 +1600,7 @@ static void io_req_link_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
>  /*
>   * Called if REQ_F_LINK_HEAD is set, and we fail the head request
>   */
> -static void io_fail_links(struct io_kiocb *req)
> +static void __io_fail_links(struct io_kiocb *req)
>  {
>  	struct io_ring_ctx *ctx = req->ctx;
>  
> @@ -1620,6 +1620,23 @@ static void io_fail_links(struct io_kiocb *req)
>  	io_cqring_ev_posted(ctx);
>  }
>  
> +static void io_fail_links(struct io_kiocb *req)
> +{
> +	struct io_ring_ctx *ctx = req->ctx;
> +
> +	if (!(req->flags & REQ_F_COMP_LOCKED)) {
> +		unsigned long flags;
> +
> +		spin_lock_irqsave(&ctx->completion_lock, flags);
> +		__io_fail_links(req);
> +		spin_unlock_irqrestore(&ctx->completion_lock, flags);
> +	} else {
> +		__io_fail_links(req);
> +	}
> +
> +	io_cqring_ev_posted(ctx);
> +}
> +
>  static void io_req_find_next(struct io_kiocb *req, struct io_kiocb **nxt)
>  {
>  	if (likely(!(req->flags & REQ_F_LINK_HEAD)))
> 

-- 
Pavel Begunkov