netdev - Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry

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Date:	Wed, 29 May 2013 13:17:52 +0400
From:	Roman Gushchin <klamm@...dex-team.ru>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Jesper Dangaard Brouer <brouer@...hat.com>,
	paulmck@...ux.vnet.ibm.com, Dipankar Sarma <dipankar@...ibm.com>,
	zhmurov@...dex-team.ru, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH v2] rcu: fix a race in hlist_nulls_for_each_entry_rcu
 macro

On 29.05.2013 04:34, Eric Dumazet wrote:
> On Tue, 2013-05-28 at 13:10 +0400, Roman Gushchin wrote:
>> On 28.05.2013 04:12, Eric Dumazet wrote:
>
>>> Adding a barrier() is probably what we want.
>>
>> I agree, inserting barrier() is also a correct and working fix.
>
> Yeah, but I can not find a clean way to put it inside the "for (;;)"

diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
index 2ae1371..74d5065 100644
--- a/include/linux/rculist_nulls.h
+++ b/include/linux/rculist_nulls.h
@@ -107,7 +107,7 @@ static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
   *
   */
  #define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member)                        \
-       for (pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));            \
+       for (({barrier();}), pos = rcu_dereference_raw(hlist_nulls_first_rcu(head)); \
                 (!is_a_nulls(pos)) &&                                           \
                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
                 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))



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