linux-kernel - Re: [PATCH net] tun: Fix xdp_rxq_info's queue

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Date: Tue, 20 Feb 2024 10:59:07 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Yunjian Wang <wangyunjian@...wei.com>, 
 willemdebruijn.kernel@...il.com, 
 jasowang@...hat.com, 
 kuba@...nel.org, 
 davem@...emloft.net
Cc: netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 brouer@...hat.com, 
 xudingke@...wei.com, 
 Yunjian Wang <wangyunjian@...wei.com>
Subject: Re: [PATCH net] tun: Fix xdp_rxq_info's queue_index when detaching

Yunjian Wang wrote:
> When a queue(tfile) is detached, we only update tfile's queue_index,
> but do not update xdp_rxq_info's queue_index. This patch fixes it.
> 
> Fixes: 8bf5c4ee1889 ("tun: setup xdp_rxq_info")
> Signed-off-by: Yunjian Wang <wangyunjian@...wei.com>
> ---
>  drivers/net/tun.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index bc80fc1d576e..be37235af55d 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -652,6 +652,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
>  				   tun->tfiles[tun->numqueues - 1]);
>  		ntfile = rtnl_dereference(tun->tfiles[index]);
>  		ntfile->queue_index = index;
> +		ntfile->xdp_rxq.queue_index = index;
>  		rcu_assign_pointer(tun->tfiles[tun->numqueues - 1],
>  				   NULL);

Does it matter that this value is stale when undetached?

It is replaced in tun_attach if previously attached:

		/* Re-attach detached tfile, updating XDP queue_index */
                WARN_ON(!xdp_rxq_info_is_reg(&tfile->xdp_rxq));

                if (tfile->xdp_rxq.queue_index    != tfile->queue_index)
                        tfile->xdp_rxq.queue_index = tfile->queue_index;