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

[Willem de Bruijn]

wangyunjian wrote:
> 
> 
> > -----Original Message-----
> > From: Willem de Bruijn [mailto:willemdebruijn.kernel@xxxxxxxxx]
> > Sent: Tuesday, February 20, 2024 11:59 PM
> > To: wangyunjian <wangyunjian@xxxxxxxxxx>;
> > willemdebruijn.kernel@xxxxxxxxx; jasowang@xxxxxxxxxx; kuba@xxxxxxxxxx;
> > davem@xxxxxxxxxxxxx
> > Cc: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > brouer@xxxxxxxxxx; xudingke <xudingke@xxxxxxxxxx>; wangyunjian
> > <wangyunjian@xxxxxxxxxx>
> > 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@xxxxxxxxxx>
> > > ---
> > >  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.

Oh yes. This looks correct to me. Let's cc: the author of the patch listed as Fixed too.

> 
> 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;