From: Manfred Schlaegl <manfred.schlaegl@gmx.at>
To: Oliver Hartkopp <socketcan@hartkopp.net>,
netdev@vger.kernel.org, davem@davemloft.net,
linux-kernel@vger.kernel.org, mkl@pengutronix.de
Subject: Re: [PATCH - regression 4.1-rc8] can: fix loss of CAN frames in raw_rcv
Date: Mon, 22 Jun 2015 12:10:14 +0200 [thread overview]
Message-ID: <5587DF06.3010509@gmx.at> (raw)
In-Reply-To: <1434905444-11438-1-git-send-email-socketcan@hartkopp.net>
Hello!
On 2015-06-21 18:50, Oliver Hartkopp wrote:
> As reported by Manfred Schlaegl here
>
> http://marc.info/?l=linux-netdev&m=143482089824232&w=2
>
> commit 514ac99c64b "can: fix multiple delivery of a single CAN frame for
> overlapping CAN filters" requires the skb->tstamp to be set to check for
> identical CAN skbs.
>
> As net timestamping is influenced by several players (netstamp_needed and
> netdev_tstamp_prequeue) Manfred missed a proper timestamp which leads to
> CAN frame loss.
>
> As skb timestamping became now mandatory for CAN related skbs this patch
> makes sure that received CAN skbs always have a proper timestamp set.
> Maybe there's a better solution in the future but this patch fixes the
> CAN frame loss so far.
>
I'm not sure, but maybe this patch (and also my original one) opens a new potential issue with timestamps.
If the timestamp is set at allocation time, this cancels setting the timestamp at delivery (by net_timestamp_check in, for example, netif_receive_skb_internal.) -> So it changes the behavior of timestamping (http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/networking/timestamping.txt?id=b953c0d234bc72e8489d3bf51a276c5c4ec85345) generally.
Hypothetical example: If timestamping is enabled by the user and there is a significant delay between allocation and delivery of a skb (early allocation in driver or something) the timestamp does not reflect the reception time anymore.
What do you thing about this?
best regards,
Manfred
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next prev parent reply other threads:[~2015-06-22 10:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-21 16:50 [PATCH - regression 4.1-rc8] can: fix loss of CAN frames in raw_rcv Oliver Hartkopp
2015-06-21 16:57 ` Marc Kleine-Budde
2015-06-21 17:10 ` Oliver Hartkopp
2015-06-22 10:10 ` Manfred Schlaegl [this message]
2015-06-22 10:34 ` Oliver Hartkopp
2015-06-22 11:49 ` Manfred Schlaegl
2015-06-22 15:09 ` Oliver Hartkopp
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