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 17:05:11 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Sasha Levin <sashal@...nel.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 09:54:01AM -0400, Sasha Levin wrote:
> 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.

So a shared maintainer trusts their co-maintainer for reviewing patches
for Linus's tree and all future kernels, but NOT into an old backported
stable tree?  I doubt that, trust should be the same for both.

thanks,

greg k-h