netdev - Re: Re: [B.A.T.M.A.N.] [PATCH] net: fix possible deadlocks in rtnl

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Message-ID: <10264267.HX5FJDguj3@sven-laptop.home.narfation.org>
Date:	Sat, 01 Dec 2012 20:04:26 +0100
From:	Sven Eckelmann <sven@...fation.org>
To:	b.a.t.m.a.n@...ts.open-mesh.org
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Simon Wunderlich <simon.wunderlich@...03.tu-chemnitz.de>,
	netdev@...r.kernel.org, davem@...emloft.net,
	Simon Wunderlich <siwu@....tu-chemnitz.de>
Subject: Re: Re: [B.A.T.M.A.N.] [PATCH] net: fix possible deadlocks in rtnl_trylock/unlock

On Saturday 01 December 2012 10:36:12 Eric Dumazet wrote:
[...]
> > diff --git a/net/batman-adv/sysfs.c b/net/batman-adv/sysfs.c
> > index 66518c7..41b74aa 100644
> > --- a/net/batman-adv/sysfs.c
> > +++ b/net/batman-adv/sysfs.c
> > @@ -635,7 +635,7 @@ static ssize_t batadv_store_mesh_iface(struct kobject
> > *kobj,> 
> >  	ret = batadv_hardif_enable_interface(hard_iface, buff);
> >  
> >  unlock:
> > -	rtnl_unlock();
> > +	__rtnl_unlock();
> > 
> >  out:
> >  	batadv_hardif_free_ref(hard_iface);
> >  	return ret;
> > 
> > diff --git a/net/bridge/br_sysfs_br.c b/net/bridge/br_sysfs_br.c
> > index c5c0593..c122782 100644
> > --- a/net/bridge/br_sysfs_br.c
> > +++ b/net/bridge/br_sysfs_br.c
> > @@ -142,7 +142,7 @@ static ssize_t store_stp_state(struct device *d,
> > 
> >  	if (!rtnl_trylock())
> >  	
> >  		return restart_syscall();
> >  	
> >  	br_stp_set_enabled(br, val);
> > 
> > -	rtnl_unlock();
> > +	__rtnl_unlock();
> > 
> >  	return len;
> >  
> >  }
> 
> I have no idea of why you believe there is a problem here.
> 
> Could you explain how net_todo_list could be not empty ?
> 
> As long as no device is unregistered between
> rtnl_trylock()/rtnl_unlock(), there is no possible deadlock.

I am not sure what "here" means for your. At least batman-adv tries to 
unregister a device -> problem [1]. I will not make any judgements about the 
other uses in the kernel/other parts patched by Simon.

Kind regards,
	Sven

[1] http://article.gmane.org/gmane.linux.kernel/1392295
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