netdev - Re: [PATCH iwl-net v3 4/6] ice: check ICE_VSI_DOWN under rtnl

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Message-ID: <Zsc1ktk/oX+LpFxl@lzaremba-mobl.ger.corp.intel.com>
Date: Thu, 22 Aug 2024 14:56:50 +0200
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
CC: <intel-wired-lan@...ts.osuosl.org>, Tony Nguyen
	<anthony.l.nguyen@...el.com>, "David S. Miller" <davem@...emloft.net>, "Jacob
 Keller" <jacob.e.keller@...el.com>, Eric Dumazet <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Alexei
 Starovoitov" <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jesper
 Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<bpf@...r.kernel.org>, <magnus.karlsson@...el.com>, Michal Kubiak
	<michal.kubiak@...el.com>, Wojciech Drewek <wojciech.drewek@...el.com>,
	Amritha Nambiar <amritha.nambiar@...el.com>, Chandan Kumar Rout
	<chandanx.rout@...el.com>
Subject: Re: [PATCH iwl-net v3 4/6] ice: check ICE_VSI_DOWN under rtnl_lock
 when preparing for reset

On Thu, Aug 22, 2024 at 01:34:33PM +0200, Maciej Fijalkowski wrote:
> On Mon, Aug 19, 2024 at 12:05:41PM +0200, Larysa Zaremba wrote:
> > Consider the following scenario:
> > 
> > .ndo_bpf()		| ice_prepare_for_reset()		|
> > ________________________|_______________________________________|
> > rtnl_lock()		|					|
> > ice_down()		|					|
> > 			| test_bit(ICE_VSI_DOWN) - true		|
> > 			| ice_dis_vsi() returns			|
> > ice_up()		|					|
> > 			| proceeds to rebuild a running VSI	|
> > 
> > .ndo_bpf() is not the only rtnl-locked callback that toggles the interface
> > to apply new configuration. Another example is .set_channels().
> > 
> > To avoid the race condition above, act only after reading ICE_VSI_DOWN
> > under rtnl_lock.
> > 
> > Fixes: 0f9d5027a749 ("ice: Refactor VSI allocation, deletion and rebuild flow")
> > Reviewed-by: Wojciech Drewek <wojciech.drewek@...el.com>
> > Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
> > Tested-by: Chandan Kumar Rout <chandanx.rout@...el.com>
> > Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> > ---
> >  drivers/net/ethernet/intel/ice/ice_lib.c | 12 ++++++------
> >  1 file changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/intel/ice/ice_lib.c b/drivers/net/ethernet/intel/ice/ice_lib.c
> > index b72338974a60..94029e446b99 100644
> > --- a/drivers/net/ethernet/intel/ice/ice_lib.c
> > +++ b/drivers/net/ethernet/intel/ice/ice_lib.c
> > @@ -2665,8 +2665,7 @@ int ice_ena_vsi(struct ice_vsi *vsi, bool locked)
> >   */
> >  void ice_dis_vsi(struct ice_vsi *vsi, bool locked)
> >  {
> > -	if (test_bit(ICE_VSI_DOWN, vsi->state))
> > -		return;
> > +	bool already_down = test_bit(ICE_VSI_DOWN, vsi->state);
> >  
> >  	set_bit(ICE_VSI_NEEDS_RESTART, vsi->state);
> >  
> > @@ -2674,15 +2673,16 @@ void ice_dis_vsi(struct ice_vsi *vsi, bool locked)
> >  		if (netif_running(vsi->netdev)) {
> >  			if (!locked)
> >  				rtnl_lock();
> > -
> > -			ice_vsi_close(vsi);
> > +			already_down = test_bit(ICE_VSI_DOWN, vsi->state);
> > +			if (!already_down)
> > +				ice_vsi_close(vsi);
> 
> ehh sorry for being sloppy reviewer. we still are testing ICE_VSI_DOWN in
> ice_vsi_close(). wouldn't all of this be cleaner if we would bail out of
> the called function when bit was already set?
>

I am not sure I see the possibility to rewrite this as you suggest, we cannot 
bail out for the netif_running() case due to needing to unlock after 
ice_vsi_close() finishes. This leaves bailing out in case of CTRL VSI and 
non-running PF, which we could do, but it would require a lengthy if condition, 
which is not that much better than nested code, IMO.

> >  
> >  			if (!locked)
> >  				rtnl_unlock();
> > -		} else {
> > +		} else if (!already_down) {
> >  			ice_vsi_close(vsi);
> >  		}
> > -	} else if (vsi->type == ICE_VSI_CTRL) {
> > +	} else if (vsi->type == ICE_VSI_CTRL && !already_down) {
> >  		ice_vsi_close(vsi);
> >  	}
> >  }
> > -- 
> > 2.43.0
> >