Re: [PATCH] io_uring/zcrx: return early from io_zcrx_recv_skb if readlen is 0

[Jens Axboe <axboe@kernel.dk>]

On 4/1/25 12:28 PM, David Wei wrote:
> When readlen is set for a recvzc request, tcp_read_sock() will call
> io_zcrx_recv_skb() one final time with len == desc->count == 0. This is
> caused by the !desc->count check happening too late. The offset + 1 !=
> skb->len happens earlier and causes the while loop to continue.
> 
> Fix this in io_zcrx_recv_skb() instead of tcp_read_sock(). Return early
> if len is 0 i.e. the read is done.

Needs a Fixes tag, which looks like it should be:

Fixes: 6699ec9a23f8 ("io_uring/zcrx: add a read limit to recvzc requests")

?

> Signed-off-by: David Wei <dw@davidwei.uk>
> ---
>  io_uring/zcrx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
> index 9c95b5b6ec4e..d1dd25e7cf4a 100644
> --- a/io_uring/zcrx.c
> +++ b/io_uring/zcrx.c
> @@ -818,6 +818,8 @@ io_zcrx_recv_skb(read_descriptor_t *desc, struct sk_buff *skb,
>  	int ret = 0;
>  
>  	len = min_t(size_t, len, desc->count);
> +	if (!len)
> +		goto out;

just return 0 here? Jumping to out would make more sense if there
are things to fixup/account at this point, but it's just going
to find offset == start_off and return 'ret', which is 0 anyway.

-- 
Jens Axboe