linux-kernel - Re: [PATCH 5.10 113/290] net: dsa: implement a central TX reallocation procedure

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Date:   Tue, 16 Mar 2021 09:54:01 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     Vladimir Oltean <vladimir.oltean@....com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Jakub Kicinski <kuba@...nel.org>,
        Christian Eggers <ceggers@...i.de>
Subject: Re: [PATCH 5.10 113/290] net: dsa: implement a central TX
 reallocation procedure

On Tue, Mar 16, 2021 at 06:46:10AM +0100, gregkh@...uxfoundation.org wrote:
>On Mon, Mar 15, 2021 at 07:56:02PM +0000, Vladimir Oltean wrote:
>> +Andrew, Vivien,
>>
>> On Mon, Mar 15, 2021 at 02:53:26PM +0100, gregkh@...uxfoundation.org wrote:
>> > From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> >
>> > From: Vladimir Oltean <vladimir.oltean@....com>
>> >
>> > [ Upstream commit a3b0b6479700a5b0af2c631cb2ec0fb7a0d978f2 ]
>> >
>> > At the moment, taggers are left with the task of ensuring that the skb
>> > headers are writable (which they aren't, if the frames were cloned for
>> > TX timestamping, for flooding by the bridge, etc), and that there is
>> > enough space in the skb data area for the DSA tag to be pushed.
>> >
>> > Moreover, the life of tail taggers is even harder, because they need to
>> > ensure that short frames have enough padding, a problem that normal
>> > taggers don't have.
>> >
>> > The principle of the DSA framework is that everything except for the
>> > most intimate hardware specifics (like in this case, the actual packing
>> > of the DSA tag bits) should be done inside the core, to avoid having
>> > code paths that are very rarely tested.
>> >
>> > So provide a TX reallocation procedure that should cover the known needs
>> > of DSA today.
>> >
>> > Note that this patch also gives the network stack a good hint about the
>> > headroom/tailroom it's going to need. Up till now it wasn't doing that.
>> > So the reallocation procedure should really be there only for the
>> > exceptional cases, and for cloned packets which need to be unshared.
>> >
>> > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
>> > Tested-by: Christian Eggers <ceggers@...i.de> # For tail taggers only
>> > Tested-by: Kurt Kanzenbach <kurt@...utronix.de>
>> > Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
>> > Signed-off-by: Jakub Kicinski <kuba@...nel.org>
>> > Signed-off-by: Sasha Levin <sashal@...nel.org>
>> > ---
>>
>> For context, Sasha explains here:
>> https://www.spinics.net/lists/stable-commits/msg190151.html
>> (the conversation is somewhat truncated, unfortunately, because
>> stable-commits@...r.kernel.org ate my replies)
>> that 13 patches were backported to get the unrelated commit 9200f515c41f
>> ("net: dsa: tag_mtk: fix 802.1ad VLAN egress") to apply cleanly with git-am.
>>
>> I am not strictly against this, even though I would have liked to know
>> that the maintainers were explicitly informed about it.
>>
>> Greg, could you make your stable backporting emails include the output
>> of ./get_maintainer.pl into the list of recipients? Thanks.
>
>I cc: everyone on the signed-off-by list on the patch, why would we need
>to add more?  A maintainer should always be on that list automatically.

Oh, hm, could this be an issue with subsystems that have a shared
maintainership model? In that scenario not all maintainers will sign-off
on a commit.

-- 
Thanks,
Sasha