From: Jesper Dangaard Brouer <brouer@redhat•com>
To: John Fastabend <john.fastabend@gmail•com>
Cc: netdev@vger•kernel.org, brouer@redhat•com
Subject: Re: [PATCH 2/2] xdp: adjust xdp redirect tracepoint to include return error code
Date: Thu, 17 Aug 2017 21:28:57 +0200 [thread overview]
Message-ID: <20170817212857.1de3f557@redhat.com> (raw)
In-Reply-To: <5995E472.70609@gmail.com>
On Thu, 17 Aug 2017 11:46:10 -0700 John Fastabend <john.fastabend@gmail•com> wrote:
> On 08/17/2017 09:22 AM, Jesper Dangaard Brouer wrote:
> > The return error code need to be included in the tracepoint
> > xdp:xdp_redirect, else its not possible to distinguish successful or
> > failed XDP_REDIRECT transmits.
> >
> > XDP have no queuing mechanism. Thus, it is fairly easily to overrun a
> > NIC transmit queue. The eBPF program invoking helpers (bpf_redirect
> > or bpf_redirect_map) to redirect a packet doesn't get any feedback
> > whether the packet was actually transmitted.
> >
> > Info on failed transmits in the tracepoint xdp:xdp_redirect, is
> > interesting as this opens for providing a feedback-loop to the
> > receiving XDP program.
> >
> > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat•com>
> > ---
>
> [...]
>
> > @@ -2532,12 +2535,14 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
> > ri->map = NULL;
> > if (unlikely(!fwd)) {
> > bpf_warn_invalid_xdp_redirect(index);
> > - return -EINVAL;
> > + err = -EINVAL;
> > + goto out;
>
> It doesn't look like there is a check in trace_xdp_redirect to
> avoid dereferencing a NULL fwd pointer here (*to in trace code
> path). Did I miss something?
Nice that you spotted this in your review, but the __string() macro
used in trace code already takes case of this, see output:
xdp:xdp_redirect: prog=39cf08f65683838a from=ixgbe2 to=(null) action=REDIRECT err=-22
> > }
> >
> > - trace_xdp_redirect(dev, fwd, xdp_prog, XDP_REDIRECT);
> > -
> > - return __bpf_tx_xdp(fwd, NULL, xdp, 0);
> > + err = __bpf_tx_xdp(fwd, NULL, xdp, 0);
> > +out:
> > + trace_xdp_redirect(dev, fwd, xdp_prog, XDP_REDIRECT, err);
> > + return err;
> > }
> > EXPORT_SYMBOL_GPL(xdp_do_redirect);
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2017-08-17 19:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-17 16:22 [PATCH 0/2] xdp: adjust xdp redirect tracepoint Jesper Dangaard Brouer
2017-08-17 16:22 ` [PATCH 1/2] ixgbe: change ndo_xdp_xmit return code on xmit errors Jesper Dangaard Brouer
2017-08-17 18:32 ` John Fastabend
2017-08-17 16:22 ` [PATCH 2/2] xdp: adjust xdp redirect tracepoint to include return error code Jesper Dangaard Brouer
2017-08-17 18:46 ` John Fastabend
2017-08-17 19:28 ` Jesper Dangaard Brouer [this message]
2017-08-17 19:43 ` John Fastabend
2017-08-18 12:29 ` Jesper Dangaard Brouer
2017-08-18 12:38 ` Daniel Borkmann
2017-08-18 23:19 ` [PATCH 0/2] xdp: adjust xdp redirect tracepoint David Miller
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170817212857.1de3f557@redhat.com \
--to=brouer@redhat$(echo .)com \
--cc=john.fastabend@gmail$(echo .)com \
--cc=netdev@vger$(echo .)kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox