Re: [PATCH iwl-net v3 4/6] ice: check ICE_VSI_DOWN under rtnl_lock when preparing for reset

[Maciej Fijalkowski]

On Thu, Aug 22, 2024 at 02:56:50PM +0200, Larysa Zaremba wrote:
> 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@xxxxxxxxx>
> > > Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
> > > Tested-by: Chandan Kumar Rout <chandanx.rout@xxxxxxxxx>
> > > Signed-off-by: Larysa Zaremba <larysa.zaremba@xxxxxxxxx>
> > > ---
> > >  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.

Hmm. I meant to move bit checking onto ice_vsi_close() only, so you would
bail out of it in case bit has already been set.

overall, ice_dis_vsi() is a very cumbersome way of calling ice_vsi_close()
:(

I guess we can progress with what you have but i'd like to brainstorm
later about some simplification around it.

I prototyped something but not tested that, just to maybe spark a
discussion. Feels easier to read and swallow in the end. Not sure if
functionality is kept:)