netdev - Re: [PATCH net-next 2/2] bpf: let bpf_warn_invalid_xdp

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Date:   Wed, 24 Nov 2021 10:13:55 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        netdev@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, bpf@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] bpf: let bpf_warn_invalid_xdp_action()
 report more info

On Mon, 2021-11-22 at 12:32 +0100, Toke Høiland-Jørgensen wrote:
> You still have:
> 
> > diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> > index 585b2b77ccc4..f7359bcb8fa3 100644
> > --- a/kernel/bpf/cpumap.c
> > +++ b/kernel/bpf/cpumap.c
> > @@ -195,7 +195,7 @@ static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu,
> >  			}
> >  			return;
> >  		default:
> > -			bpf_warn_invalid_xdp_action(act);
> > +			bpf_warn_invalid_xdp_action(skb->dev, rcpu->prog, act);
> >  			fallthrough;
> >  		case XDP_ABORTED:
> >  			trace_xdp_exception(skb->dev, rcpu->prog, act);
> > @@ -254,7 +254,7 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
> >  			}
> >  			break;
> >  		default:
> > -			bpf_warn_invalid_xdp_action(act);
> > +			bpf_warn_invalid_xdp_action(xdpf->dev_rx, rcpu->prog, act);
> >  			fallthrough;
> >  		case XDP_DROP:
> >  			xdp_return_frame(xdpf);
> > diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> > index f02d04540c0c..79bcf2169881 100644
> > --- a/kernel/bpf/devmap.c
> > +++ b/kernel/bpf/devmap.c
> > @@ -348,7 +348,7 @@ static int dev_map_bpf_prog_run(struct bpf_prog *xdp_prog,
> >  				frames[nframes++] = xdpf;
> >  			break;
> >  		default:
> > -			bpf_warn_invalid_xdp_action(act);
> > +			bpf_warn_invalid_xdp_action(dev, xdp_prog, act);
> >  			fallthrough;
> >  		case XDP_ABORTED:
> >  			trace_xdp_exception(dev, xdp_prog, act);
> > @@ -507,7 +507,7 @@ static u32 dev_map_bpf_prog_run_skb(struct sk_buff *skb, struct bpf_dtab_netdev
> >  		__skb_push(skb, skb->mac_len);
> >  		break;
> >  	default:
> > -		bpf_warn_invalid_xdp_action(act);
> > +		bpf_warn_invalid_xdp_action(dst->dev, dst->xdp_prog, act);
> >  		fallthrough;
> >  	case XDP_ABORTED:
> >  		trace_xdp_exception(dst->dev, dst->xdp_prog, act);
> 
> ... and ...
> 
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 3ba584bb23f8..658f7a84d9bc 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -8179,13 +8179,13 @@ static bool xdp_is_valid_access(int off, int size,
> >  	return __is_valid_xdp_access(off, size);
> >  }
> >  
> > -void bpf_warn_invalid_xdp_action(u32 act)
> > +void bpf_warn_invalid_xdp_action(struct net_device *dev, struct bpf_prog *prog, u32 act)
> >  {
> >  	const u32 act_max = XDP_REDIRECT;
> >  
> > -	pr_warn_once("%s XDP return value %u, expect packet loss!\n",
> > +	pr_warn_once("%s XDP return value %u on prog %s (id %d) dev %s, expect packet loss!\n",
> >  		     act > act_max ? "Illegal" : "Driver unsupported",
> > -		     act);
> > +		     act, prog->aux->name, prog->aux->id, dev->name);
> >  }
> >  EXPORT_SYMBOL_GPL(bpf_warn_invalid_xdp_action);
> 
> This will still print the dev name for cpumap and devmap programs, which
> is misleading - it will have people looking at the drivers when the
> problem is somewhere else.
> 
> I pointed this out multiple times in comments on your last revision so
> I'm a bit puzzled as to why you're still doing this? :/

I'm sorry, quite a bit of relevant incoming messages keep landing in
the spam folder due to corporate/gmail filters.

> Just pass NULL as the dev from cpumap/devmap and don't print the dev
> name in this case...

No opposition on my side, but I think that is a bit conflicting with
Alexei suggestion of keeping the message handling as simple as
possible?!?

@Alexei, would something like the following:

	pr_warn_once("%s XDP return value %u on prog %s (id %d) dev %s, expect packet loss!\n",
  		     act > act_max ? "Illegal" : "Driver unsupported",
		     act, prog->aux->name, prog->aux->id, dev ? dev->name, "");

fit you?

Thanks!

Paolo