netdev - RE: [PATCH net] ice: Fix race during aux device (un)plugging

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Message-ID: <MW5PR11MB5811D6D5245206C5A37B803DDDEE9@MW5PR11MB5811.namprd11.prod.outlook.com>
Date:   Fri, 15 Apr 2022 17:53:44 +0000
From:   "Ertman, David M" <david.m.ertman@...el.com>
To:     ivecera <ivecera@...hat.com>, mschmidt <mschmidt@...hat.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        poros <poros@...hat.com>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "Saleem, Shiraz" <shiraz.saleem@...el.com>,
        "moderated list:INTEL ETHERNET DRIVERS" 
        <intel-wired-lan@...ts.osuosl.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net] ice: Fix race during aux device (un)plugging

> -----Original Message-----
> From: Ivan Vecera <ivecera@...hat.com>
> Sent: Friday, April 15, 2022 8:50 AM
> To: mschmidt <mschmidt@...hat.com>
> Cc: netdev@...r.kernel.org; poros <poros@...hat.com>; Brandeburg,
> Jesse <jesse.brandeburg@...el.com>; Nguyen, Anthony L
> <anthony.l.nguyen@...el.com>; David S. Miller <davem@...emloft.net>;
> Jakub Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>;
> Saleem, Shiraz <shiraz.saleem@...el.com>; Ertman, David M
> <david.m.ertman@...el.com>; moderated list:INTEL ETHERNET DRIVERS
> <intel-wired-lan@...ts.osuosl.org>; open list <linux-kernel@...r.kernel.org>
> Subject: Re: [PATCH net] ice: Fix race during aux device (un)plugging
> 
> On Fri, 15 Apr 2022 13:12:03 +0200
> Michal Schmidt <mschmidt@...hat.com> wrote:
> 
> > On Thu, Apr 14, 2022 at 6:39 PM Ivan Vecera <ivecera@...hat.com> wrote:
> >
> > > Function ice_plug_aux_dev() assigns pf->adev field too early prior
> > > aux device initialization and on other side ice_unplug_aux_dev()
> > > starts aux device deinit and at the end assigns NULL to pf->adev.
> > > This is wrong and can causes a crash when ice_send_event_to_aux()
> > > call occurs during these operations because that function depends
> > > on non-NULL value of pf->adev and does not assume that aux device
> > > is half-initialized or half-destroyed.
> > >
> > > Modify affected functions so pf->adev field is set after aux device
> > > init and prior aux device destroy.
> > >
> > [...]
> >
> > > @@ -320,12 +319,14 @@ int ice_plug_aux_dev(struct ice_pf *pf)
> > >   */
> > >  void ice_unplug_aux_dev(struct ice_pf *pf)
> > >  {
> > > -       if (!pf->adev)
> > > +       struct auxiliary_device *adev = pf->adev;
> > > +
> > > +       if (!adev)
> > >                 return;
> > >
> > > -       auxiliary_device_delete(pf->adev);
> > > -       auxiliary_device_uninit(pf->adev);
> > >         pf->adev = NULL;
> > > +       auxiliary_device_delete(adev);
> > > +       auxiliary_device_uninit(adev);
> > >  }
> > >
> >
> > Hi Ivan,
> > What prevents ice_unplug_aux_dev() from running immediately after
> > ice_send_event_to_aux() gets past its "if (!pf->adev)" test ?
> > Michal
> 
> ice_send_event_to_aux() takes aux device lock. ice_unplug_aux_dev()
> calls auxiliary_device_delete() that calls device_del(). device_del()
> takes device_lock() prior kill_device(). So if ice_send_event_to_aux()
> is in progress then device_del() waits for its completion.
> 
> Thanks,
> Ivan

Thanks for the patch Ivan!

Reviewed-by: Dave Ertman <david.m.ertman@...el.com>