Re: conntrack, suspicious RCU usage

[Hans Schillstrom <hans.schillstrom@ericsson.com>]

On Wednesday 11 January 2012 14:33:55 Eric Dumazet wrote:
> Le mercredi 11 janvier 2012 à 14:24 +0100, Hans Schillstrom a écrit :
> > On Wednesday 11 January 2012 11:01:51 Eric Dumazet wrote:
> 
> > > Hmm, we either need to take rcu_read_lock() while calling
> > > __nf_ct_l3proto_find(), or define a variant using
> > > rcu_dereference_protected() in places we hold nf_conntrack_lock
> > > 
> > I made a qick test with locks /unlocks in
> > __nf_ct_l3proto_find() and __nf_ct_l4proto_find()
> > 
> > 	rcu_read_lock();
> > ...
> > 	rcu_read_unlock();
> > 	return retp;
> > 
> > It seems to help, I cant see the dump anymore and everything else that I run works ...
> > 
> > 
> 
> You cant do that, its just a brown paper bag :)
> 
OK it didn't feel right ...

> If "retp" is returned, then the caller must handle the rcu_read_unlock()
> itself, after all possible "retp" dereferences.
> 
> But really adding rcu_read_lock() should not be necessary on paths we
> own the conntrack lock. We should use rcu_dereference_protected()
> instead.
> 
> I'll send a patch.

Thanks
Hans
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