Re: [PATCH] wl12xx: Fix kernel crash related to hw recovery and interface shutdown

[Luciano Coelho <luciano.coelho@nokia.com>]

On Tue, 2010-11-23 at 07:51 +0200, Juuso Oikarinen wrote:
> On Mon, 2010-11-22 at 14:52 +0200, Luciano Coelho wrote:
> > On Thu, 2010-11-18 at 15:19 +0200, juuso.oikarinen@nokia.com wrote:
> > > From: Juuso Oikarinen <juuso.oikarinen@nokia.com>
> > > 
> > > It is possible that the op_remove_interface function  is invoked exactly at
> > > the same time has hw recovery is started. In this case it is possible for the
> > > interface to be already removed in the op_remove_interface call, which
> > > currently leads to a kernel warning and a subsequent kernel crash.
> > > 
> > > Fix this by ignoring the op_remove_interface call if the interface is already
> > > down at that point.
> > > 
> > > Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
> > > ---
> > 
> > [...]
> > 
> > > diff --git a/drivers/net/wireless/wl12xx/main.c b/drivers/net/wireless/wl12xx/main.c
> > > index 31f0e2f..11b0477 100644
> > > --- a/drivers/net/wireless/wl12xx/main.c
> > > +++ b/drivers/net/wireless/wl12xx/main.c
> > > @@ -1157,10 +1157,16 @@ static void wl1271_op_remove_interface(struct ieee80211_hw *hw,
> > >  	struct wl1271 *wl = hw->priv;
> > >  
> > >  	mutex_lock(&wl->mutex);
> > > -	WARN_ON(wl->vif != vif);
> > > -	__wl1271_op_remove_interface(wl);
> > > -	mutex_unlock(&wl->mutex);
> > > +	/*
> > > +	 * wl->vif can be null here if someone shuts down the interface
> > > +	 * just when hardware recovery has been started.
> > > +	 */
> > > +	if (wl->vif) {
> > > +		WARN_ON(wl->vif != vif);
> > > +		__wl1271_op_remove_interface(wl);
> > > +	}
> > 
> > Should you still remove the interface if the vif you received is wrong?
> > Surely, something is totally wrong if you get a different vif, but maybe
> > removing the interface here will just confuse things even more?
> 
> Dunno if it would be better to remove or leave unremoved - probably does
> not matter. If the vif is wrong, there is some serious bug somewhere,
> and probably the result is serious instability anyway.
> 
> The WARN_ON is there just to validate the assumption the driver makes
> about the vif, and this function call. If there is a bug somewhere, or
> the assumption somehow changes, the warning will be a clear indication
> of it.

Yep, it's okay like this.  And it was like that earlier anyway.  I was
just wondering if it would be possible for a similar thing as wl->vif
being NULL (which your patch addresses) happen, such as wl->vif changing
before we had the chance to fully remove the interface.  It will
probably not happen and, as you say, the WARN_ON will be a good
indication that something went wrong.

Applied to wl12xx/master.  Thanks!


-- 
Cheers,
Luca.