netdev - Re: mmotm 2010-04-28

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Message-ID: <20100503181629.GJ2597@linux.vnet.ibm.com>
Date:	Mon, 3 May 2010 11:16:29 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Valdis.Kletnieks@...edu, Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: mmotm 2010-04-28 - RCU whinges

On Mon, May 03, 2010 at 06:14:53PM +0200, Eric Dumazet wrote:
> Le lundi 03 mai 2010 à 08:43 -0700, Paul E. McKenney a écrit :
> 
> > Highly recommended.  ;-)
> > 
> > And thanks to you for your testing efforts and to Eric for the fixes!!!
> > 
> 
> For this last one, I think you should push following patch Paul

I would be happy to if I could find the commit creating
hlist_for_each_entry_continue_rcu()...

I do see a ca. 2008 patch from Stephen Hemminger:

	http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg264661.html

According to http://patchwork.ozlabs.org/patch/47997/, this is
going up the networking tree as of March 18, 2010.

So I would be happy to push the patch below, but to do so, I will need
to adopt the portion of Stephen's patch that created this primitive.

Please let me know how you would like to proceed!

							Thanx, Paul

> Followup of commit 3120438ad6
> (rcu: Disable lockdep checking in RCU list-traversal primitives)
> 
> Or we might introduce a hlist_for_each_entry_continue_rcu_bh() macro...
> 
> 
> 
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index 004908b..b0c7e24 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -435,10 +435,10 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev,
>   * @member:	the name of the hlist_node within the struct.
>   */
>  #define hlist_for_each_entry_continue_rcu(tpos, pos, member)		\
> -	for (pos = rcu_dereference((pos)->next);			\
> +	for (pos = rcu_dereference_raw((pos)->next);			\
>  	     pos && ({ prefetch(pos->next); 1; }) &&			\
>  	     ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1; });  \
> -	     pos = rcu_dereference(pos->next))
> +	     pos = rcu_dereference_raw(pos->next))
> 
> 
>  #endif	/* __KERNEL__ */
> 
> 
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