linux-kernel - Re: [PATCH v2] io_uring: Fix reversed nonblock flag

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Date:   Fri, 4 Oct 2019 07:05:21 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Pavel Begunkov (Silence)" <asml.silence@...il.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH v2] io_uring: Fix reversed nonblock flag

On 10/4/19 4:07 AM, Pavel Begunkov (Silence) wrote:
> From: Pavel Begunkov <asml.silence@...il.com>
> 
> io_queue_link_head() accepts @force_nonblock flag, but io_ring_submit()
> passes something opposite.
> 
> v2: fix build error by test robot: Rebase from custom tree
> Reported-by: kbuild test robot <lkp@...el.com>
> 
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
>   fs/io_uring.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index c934f91c51e9..c909ea2b84e9 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2703,6 +2703,7 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit,
>   	struct io_kiocb *shadow_req = NULL;
>   	bool prev_was_link = false;
>   	int i, submit = 0;
> +	bool force_nonblock = true;
>   
>   	if (to_submit > IO_PLUG_THRESHOLD) {
>   		io_submit_state_start(&state, ctx, to_submit);
> @@ -2710,9 +2711,9 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit,
>   	}
>   
>   	for (i = 0; i < to_submit; i++) {
> -		bool force_nonblock = true;
>   		struct sqe_submit s;
>   
> +		force_nonblock = true;
>   		if (!io_get_sqring(ctx, &s))
>   			break;
>   
> @@ -2761,7 +2762,7 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit,
>   
>   	if (link)
>   		io_queue_link_head(ctx, link, &link->submit, shadow_req,
> -					block_for_last);
> +					force_nonblock);
>   	if (statep)
>   		io_submit_state_end(statep);

Shouldn't this just be:

   		io_queue_link_head(ctx, link, &link->submit, shadow_req,
 					!block_for_last);

We're outside the loop, so by definition at the end of what we need to
do. We don't need to factor in the fiddling of force_nonblock here,
it'll be false at this point anyway. Only exception is error handling,
if the caller asked for more than what was in the ring. Not a big
deal...

-- 
Jens Axboe