netdev - Re: [Intel-wired-lan] [PATCH iwl-next v2 3/3] igb: allow configuring RSS key via ethtool set

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Message-ID: <20260116062410.80174-2-takkozu@amazon.com>
Date: Fri, 16 Jan 2026 15:24:11 +0900
From: Takashi Kozu <takkozu@...zon.com>
To: <aleksandr.loktionov@...el.com>
CC: <andrew+netdev@...n.ch>, <anthony.l.nguyen@...el.com>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <enjuk@...zon.com>,
	<intel-wired-lan@...ts.osuosl.org>, <kuba@...nel.org>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>,
	<przemyslaw.kitszel@...el.com>, <takkozu@...zon.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v2 3/3] igb: allow configuring RSS key via ethtool set_rxfh

> -----Original Message-----
> From: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>
> To: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>,
> Kohei Enju <enjuk@...zon.com>
> Cc: "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
> "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
> "davem@...emloft.net" <davem@...emloft.net>,
> "edumazet@...gle.com" <edumazet@...gle.com>,
> "intel-wired-lan@...ts.osuosl.org"
> <intel-wired-lan@...ts.osuosl.org>,
> "kuba@...nel.org" <kuba@...nel.org>,
> "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
> "pabeni@...hat.com" <pabeni@...hat.com>,
> "Kitszel, Przemyslaw" <przemyslaw.kitszel@...el.com>,
> "takkozu@...zon.com" <takkozu@...zon.com>
> Subject: Re: [Intel-wired-lan] [PATCH iwl-next v2 3/3] igb: allow configuring RSS key via ethtool set_rxfh
> Date: Thu, 8 Jan 2026 13:03:12 +0000 [thread overview]
> Message-ID: <IA3PR11MB898612B0CDA9C5A5448733EEE585A@...PR11MB8986.namprd11.prod.outlook.com> (raw)
> In-Reply-To: <IA3PR11MB89865D0189D37BB3393B57F5E585A@...PR11MB8986.namprd11.prod.outlook.com>
> 
> 
> 
> > -----Original Message-----
> > From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf
> > Of Loktionov, Aleksandr
> > Sent: Thursday, January 8, 2026 1:28 PM
> > To: Kohei Enju <enjuk@...zon.com>
> > Cc: andrew+netdev@...n.ch; Nguyen, Anthony L
> > <anthony.l.nguyen@...el.com>; davem@...emloft.net;
> > edumazet@...gle.com; intel-wired-lan@...ts.osuosl.org;
> > kuba@...nel.org; netdev@...r.kernel.org; pabeni@...hat.com; Kitszel,
> > Przemyslaw <przemyslaw.kitszel@...el.com>; takkozu@...zon.com
> > Subject: Re: [Intel-wired-lan] [PATCH iwl-next v2 3/3] igb: allow
> > configuring RSS key via ethtool set_rxfh
> >
> >
> >
> > > -----Original Message-----
> > > From: Kohei Enju <enjuk@...zon.com>
> > > Sent: Thursday, January 8, 2026 1:04 PM
> > > To: Loktionov, Aleksandr <aleksandr.loktionov@...el.com>
> > > Cc: andrew+netdev@...n.ch; Nguyen, Anthony L
> > > <anthony.l.nguyen@...el.com>; davem@...emloft.net;
> > > edumazet@...gle.com; enjuk@...zon.com; intel-wired-
> > > lan@...ts.osuosl.org; kuba@...nel.org; netdev@...r.kernel.org;
> > > pabeni@...hat.com; Kitszel, Przemyslaw
> > <przemyslaw.kitszel@...el.com>;
> > > takkozu@...zon.com
> > > Subject: Re: RE: [Intel-wired-lan] [PATCH iwl-next v2 3/3] igb:
> > allow
> > > configuring RSS key via ethtool set_rxfh
> > >
> > > On Thu, 8 Jan 2026 07:29:19 +0000, Loktionov, Aleksandr wrote:
> > >
> > > >>
> > > >> - igb_write_rss_indir_tbl(adapter);
> > > >> + if (rxfh->key) {
> > > >> + adapter->has_user_rss_key = true;
> > > >> + memcpy(adapter->rss_key, rxfh->key, sizeof(adapter-
> > > >> >rss_key));
> > > >> + igb_write_rss_key(adapter);
> > > >It leads to race between ethtool RSS update and concurrent resets.
> > > >Because igb_setup_mrqc() (called during resets) also calls
> > > igb_write_rss_key(adapter).
> > > >Non-fatal but breaks RSS configuration guarantees.
> > >
> > > At my first glance, rtnl lock serializes those operation, so it
> > > doesn't seem to be racy as long as they are under the rtnl lock.
> > >
> > > As far as I skimmed the codes, functions such as igb_open()/
> > > igb_up()/igb_reset_task(), which finally call igb_write_rss_key()
> > are
> > > serialized by rtnl lock or serializes igb_write_rss_key() call by
> > > locking rtnl.
> > >
> > > Please let me know if I'm missing something and it's truly racy.
> > I think you're right, and I've missed that missing rtnl_lock was added
> > in upstream.
> >
> > Thank you for clarification
> > Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@...el.com>
> >
> 
> Afterthought, I think it could be nice to place ASSERT_RTNL() to show it explicitly.
> What do you think about this idea?

Sorry for the late reply. 
I think it's a good idea. I will add ASSERT_RTNL().