netdev - Re: [PATCH] af_packet: Fix softirq mismatch in tpacket

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Message-ID: <66ed3904738bb_3136a8294eb@willemb.c.googlers.com.notmuch>
Date: Fri, 20 Sep 2024 04:57:40 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Ben Greear <greearb@...delatech.com>, 
 David Ahern <dsahern@...nel.org>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 netdev@...r.kernel.org, 
 Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH] af_packet: Fix softirq mismatch in tpacket_rcv

Ben Greear wrote:
> On 9/19/24 13:00, David Ahern wrote:
> > On 9/19/24 10:44 AM, Willem de Bruijn wrote:
> >> Yes, it seems that VRF calls dev_queue_xmit_nit without the same BH
> >> protections that it expects.
> >>
> >> I suspect that the fix is in VRF, to disable BH the same way that
> >> __dev_queue_xmit does, before calling dev_queue_xmit_nit.
> >>
> > 
> > commit 504fc6f4f7f681d2a03aa5f68aad549d90eab853 removed the bh around
> > dev_queue_xmit_nit:
> > 
> > diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
> > index 6043e63b42f9..43f374444684 100644
> > --- a/drivers/net/vrf.c
> > +++ b/drivers/net/vrf.c
> > @@ -638,9 +638,7 @@ static void vrf_finish_direct(struct sk_buff *skb)
> >                  eth_zero_addr(eth->h_dest);
> >                  eth->h_proto = skb->protocol;
> > 
> > -               rcu_read_lock_bh();
> >                  dev_queue_xmit_nit(skb, vrf_dev);
> > -               rcu_read_unlock_bh();
> > 
> >                  skb_pull(skb, ETH_HLEN);
> >          }
> 
> So I guess we should revert this? 

Looks like it to me.

In which case good to not just revert, but explain why, and probably
copy the comment that is present in __dev_queue_xmit.

> Maybe original testing passed because veth doesn't do
> xmit/rcv quite like a real Eth driver will?
>
> Thanks,
> Ben
> 
> -- 
> Ben Greear <greearb@...delatech.com>
> Candela Technologies Inc  http://www.candelatech.com
> 
>