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

[Takashi Kozu <takkozu@amazon.com>]

> -----Original Message-----
> From: "Loktionov, Aleksandr" <aleksandr.loktionov@intel.com>
> To: "Loktionov, Aleksandr" <aleksandr.loktionov@intel.com>,
> Kohei Enju <enjuk@amazon.com>
> Cc: "andrew+netdev@lunn.ch" <andrew+netdev@lunn.ch>,
> "Nguyen, Anthony L" <anthony.l.nguyen@intel.com>,
> "davem@davemloft.net" <davem@davemloft.net>,
> "edumazet@google.com" <edumazet@google.com>,
> "intel-wired-lan@lists.osuosl.org"
> <intel-wired-lan@lists.osuosl.org>,
> "kuba@kernel.org" <kuba@kernel.org>,
> "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
> "pabeni@redhat.com" <pabeni@redhat.com>,
> "Kitszel, Przemyslaw" <przemyslaw.kitszel@intel.com>,
> "takkozu@amazon.com" <takkozu@amazon.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@IA3PR11MB8986.namprd11.prod.outlook.com> (raw)
> In-Reply-To: <IA3PR11MB89865D0189D37BB3393B57F5E585A@IA3PR11MB8986.namprd11.prod.outlook.com>
> 
> 
> 
> > -----Original Message-----
> > From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf
> > Of Loktionov, Aleksandr
> > Sent: Thursday, January 8, 2026 1:28 PM
> > To: Kohei Enju <enjuk@amazon.com>
> > Cc: andrew+netdev@lunn.ch; Nguyen, Anthony L
> > <anthony.l.nguyen@intel.com>; davem@davemloft.net;
> > edumazet@google.com; intel-wired-lan@lists.osuosl.org;
> > kuba@kernel.org; netdev@vger.kernel.org; pabeni@redhat.com; Kitszel,
> > Przemyslaw <przemyslaw.kitszel@intel.com>; takkozu@amazon.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@amazon.com>
> > > Sent: Thursday, January 8, 2026 1:04 PM
> > > To: Loktionov, Aleksandr <aleksandr.loktionov@intel.com>
> > > Cc: andrew+netdev@lunn.ch; Nguyen, Anthony L
> > > <anthony.l.nguyen@intel.com>; davem@davemloft.net;
> > > edumazet@google.com; enjuk@amazon.com; intel-wired-
> > > lan@lists.osuosl.org; kuba@kernel.org; netdev@vger.kernel.org;
> > > pabeni@redhat.com; Kitszel, Przemyslaw
> > <przemyslaw.kitszel@intel.com>;
> > > takkozu@amazon.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@intel.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().