RE: [PATCH net] tun: Fix xdp_rxq_info's queue_index when detaching

[wangyunjian <wangyunjian@huawei.com>]

> -----Original Message-----
> From: Willem de Bruijn [mailto:willemdebruijn.kernel@gmail.com]
> Sent: Tuesday, February 20, 2024 11:59 PM
> To: wangyunjian <wangyunjian@huawei.com>;
> willemdebruijn.kernel@gmail.com; jasowang@redhat.com; kuba@kernel.org;
> davem@davemloft.net
> Cc: netdev@vger.kernel.org; linux-kernel@vger.kernel.org;
> brouer@redhat.com; xudingke <xudingke@huawei.com>; wangyunjian
> <wangyunjian@huawei.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@huawei.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?

Yes, the detach tfile'queue_index is not important because the re-attach will update.
But this patch is to fix the 'ntfile'(that replaces the detach tfile)'s queue_index, it is wrong.

Thanks
> 
> 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;