linux-kernel - Re: BUG: scheduling while atomic: ifconfig/0x00000002/4170

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Date:	Fri, 7 Sep 2007 07:25:38 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>, satyam@...radead.org,
	flo@...822.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
	michal.k.k.piotrowski@...il.com,
	ipw3945-devel@...ts.sourceforge.net, yi.zhu@...el.com,
	flamingice@...rmilk.net
Subject: Re: BUG: scheduling while atomic: ifconfig/0x00000002/4170

On Fri, Sep 07, 2007 at 03:27:15PM +0200, Johannes Berg wrote:
> On Thu, 2007-09-06 at 08:46 -0700, Paul E. McKenney wrote:
> 
> > Looks good to me from an RCU viewpoint.  I cannot claim familiarity with
> > this code.  I therefore especially like the indications of where RTNL
> > is held and not!!!
> 
> :)
> 
> > Some questions below based on a quick scan.  And a global question:
> > should the comments about RTNL being held be replaced by ASSERT_RTNL()?
> 
> I don't like ASSERT_RTNL() much because it actually tries to lock it.
> I'd be much happer if it was WARN_ON(!mutex_locked(&rtnl_mutex)) or
> something equivalent.

Ah!  It would indeed be nice to have a lower-overhead ASSERT_RTNL_LIGHT()
or whatever.

> In any case, I have an updated patch I'll be sending soon, and it
> requires a new list walking primitive I'll also send.

Look forward to seeing it!

> > > -	write_lock_bh(&local->sub_if_lock);
> > > +	/* we're under RTNL so all this is fine */
> > >  	if (unlikely(local->reg_state == IEEE80211_DEV_UNREGISTERED)) {
> > > -		write_unlock_bh(&local->sub_if_lock);
> > >  		__ieee80211_if_del(local, sdata);
> > >  		return -ENODEV;
> > >  	}
> > > -	list_add(&sdata->list, &local->sub_if_list);
> > > +	list_add_tail_rcu(&sdata->list, &local->interfaces);
> > 
> > The _rcu is required because this list isn't protected by RTNL?
> 
> Yes, not all walkers of the list are protected by the RTNL.

K.

> > > @@ -226,22 +225,22 @@ void ieee80211_if_reinit(struct net_devi
> > >  		/* Remove all virtual interfaces that use this BSS
> > >  		 * as their sdata->bss */
> > >  		struct ieee80211_sub_if_data *tsdata, *n;
> > > -		LIST_HEAD(tmp_list);
> > > 
> > > -		write_lock_bh(&local->sub_if_lock);
> > 
> > This code is also protected by RTNL?
> 
> Yes.

Comment?  (Or is it in the function header?)

> > >  	ASSERT_RTNL();
> > 
> > I -like- this!!!  ;-)
> 
> :)

							Thanx, Paul
-
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