netdev - Re: [PATCH net-next 5/8] rtnetlink: do not depend on RTNL for many attributes

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Message-ID: <20240507163814.GE15955@kernel.org>
Date: Tue, 7 May 2024 17:38:14 +0100
From: Simon Horman <horms@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 5/8] rtnetlink: do not depend on RTNL for many
 attributes

On Sun, May 05, 2024 at 05:14:58PM +0200, Eric Dumazet wrote:
> On Sun, May 5, 2024 at 5:06 PM Simon Horman <horms@...nel.org> wrote:
> >
> > On Sun, May 05, 2024 at 05:00:10PM +0200, Eric Dumazet wrote:
> > > On Sun, May 5, 2024 at 4:47 PM Simon Horman <horms@...nel.org> wrote:
> > > >
> > > > On Fri, May 03, 2024 at 07:20:56PM +0000, Eric Dumazet wrote:
> > > > > Following device fields can be read locklessly
> > > > > in rtnl_fill_ifinfo() :
> > > > >
> > > > > type, ifindex, operstate, link_mode, mtu, min_mtu, max_mtu, group,
> > > > > promiscuity, allmulti, num_tx_queues, gso_max_segs, gso_max_size,
> > > > > gro_max_size, gso_ipv4_max_size, gro_ipv4_max_size, tso_max_size,
> > > > > tso_max_segs, num_rx_queues.
> > > >
> > > > Hi Eric,
> > > >
> > > > * Regarding mtu, as the comment you added to sruct net_device
> > > >   some time ago mentions, mtu is written in many places.
> > > >
> > > >   I'm wondering if, in particular wrt ndo_change_mtu implementations,
> > > >   if some it is appropriate to add WRITE_ONCE() annotations.
> > >
> > > Sure thing. I called for these changes in commit
> > > 501a90c94510 ("inet: protect against too small mtu values.")
> > > when I said "Hopefully we will add the missing ones in followup patches."
> >
> > Ok, so basically it would be nice to add them,
> > but they don't block progress of this patchset?
> 
> A patch set adding WRITE_ONCE() on all dev->mtu would be great,
> and seems orthogonal.

Ack. I'm guessing an incremental approach to getting better coverage would
be best. I'll add this to my todo list.

> Note that we already have many points in the
> stack where dev->mtu is read locklessly.

Understood.

For the record, I have no objections to this patch.

Reviewed-by: Simon Horman <horms@...nel.org>