netdev - Re: suspicious RCU usage (netlink/rhashtable)

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Message-ID: <20151222215400.GA14148@codemonkey.org.uk>
Date:	Tue, 22 Dec 2015 16:54:00 -0500
From:	Dave Jones <davej@...emonkey.org.uk>
To:	David Miller <davem@...emloft.net>
Cc:	kraigatgoog@...il.com, netdev@...r.kernel.org,
	herbert@...dor.apana.org.au
Subject: Re: suspicious RCU usage (netlink/rhashtable)

On Tue, Dec 22, 2015 at 04:50:20PM -0500, David Miller wrote:
 
 > >  > > Simple fix is below.  Though, I don't understand the history of the
 > >  > > multiple locks in this structure to be sure it's correct.  I'll send
 > >  > > it as a formal patch.  Please reject if it's not the right approach.
 > >  > > 
 > >  > > diff --git a/lib/rhashtable.c b/lib/rhashtable.c
 > >  > > index 1c149e9..cc80870 100644
 > >  > > --- a/lib/rhashtable.c
 > >  > > +++ b/lib/rhashtable.c
 > >  > > @@ -516,7 +516,8 @@ int rhashtable_walk_init(struct rhashtable *ht,
 > >  > > struct rhashtable_iter *iter)
 > >  > >                 return -ENOMEM;
 > >  > > 
 > >  > >         spin_lock(&ht->lock);
 > >  > > -       iter->walker->tbl = rht_dereference(ht->tbl, ht);
 > >  > > +       iter->walker->tbl =
 > >  > > +               rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));
 > >  > >         list_add(&iter->walker->list, &iter->walker->tbl->walkers);
 > >  > >         spin_unlock(&ht->lock);
 > >  > 
 > >  > How can this be the "fix"?  That's exactly what's in the tree.
 > > 
 > > I should have made clear, this is Linus' tree I'm hitting this on,
 > > which matches what Craig posted.
 > 
 > Ok, so this should be fixed in my 'net' tree and I'll send that to Linus
 > soon.

Great, thanks Dave.  Sorry for the fire-alarm :)

	Dave
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