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

[Sasha Levin]

On Tue, Mar 16, 2021 at 06:46:10AM +0100, gregkh@xxxxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxxxxxx wrote:
> > > From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > >
> > > From: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> > >
> > > [ 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@xxxxxxx>
> > > Tested-by: Christian Eggers <ceggers@xxxxxxx> # For tail taggers only
> > > Tested-by: Kurt Kanzenbach <kurt@xxxxxxxxxxxxx>
> > > Reviewed-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> > > Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
> > > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > > ---
> >
> > For context, Sasha explains here:
> > https://www.spinics.net/lists/stable-commits/msg190151.html
> > (the conversation is somewhat truncated, unfortunately, because
> > stable-commits@xxxxxxxxxxxxxxx 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