From: John Fastabend <john.fastabend@gmail•com>
To: Jesper Dangaard Brouer <brouer@redhat•com>
Cc: netdev@vger•kernel.org
Subject: Re: [PATCH 2/2] xdp: adjust xdp redirect tracepoint to include return error code
Date: Thu, 17 Aug 2017 12:43:18 -0700 [thread overview]
Message-ID: <5995F1D6.8040103@gmail.com> (raw)
In-Reply-To: <20170817212857.1de3f557@redhat.com>
On 08/17/2017 12:28 PM, Jesper Dangaard Brouer wrote:
>
> 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);
I think we should drop the warn_invalid now that we have a tracepoint.
The tracepoint is much nicer for debugging vs a warning for what might
be a valid case depending on xdp program.
>>> - 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
Great thanks.
next prev parent reply other threads:[~2017-08-17 19:43 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
2017-08-17 19:43 ` John Fastabend [this message]
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
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