From: Roman Gushchin <klamm@yandex-team•ru>
To: paulmck@linux•vnet.ibm.com
Cc: Dipankar Sarma <dipankar@in•ibm.com>,
zhmurov@yandex-team•ru, linux-kernel@vger•kernel.org,
netdev@vger•kernel.org, "David S. Miller" <davem@davemloft•net>,
Eric Dumazet <eric.dumazet@gmail•com>,
Alexey Kuznetsov <kuznet@ms2•inr.ac.ru>,
James Morris <jmorris@namei•org>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6•org>,
Patrick McHardy <kaber@trash•net>
Subject: Re: [PATCH] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro
Date: Tue, 21 May 2013 16:46:54 +0400 [thread overview]
Message-ID: <519B6CBE.1020002@yandex-team.ru> (raw)
In-Reply-To: <20130521120906.GD3578@linux.vnet.ibm.com>
On 21.05.2013 16:09, Paul E. McKenney wrote:
> On Tue, May 21, 2013 at 01:05:48PM +0400, Roman Gushchin wrote:
>> Hi, all!
>>
>> This is a fix for a problem described here:
>> https://lkml.org/lkml/2013/4/16/371 .
>> ---
>>
>> Some network functions (udp4_lib_lookup2(), for instance) use the
>> hlist_nulls_for_each_entry_rcu macro in a way that assumes restarting
>> of a loop. In this case, it is strictly necessary to reread the head->first
>> value from the memory before each scan.
>> Without additional hints, gcc caches this value in a register. In this case,
>> if a cached node is moved to another chain during the scan, we can loop
>> forever getting wrong nulls values and restarting the loop uninterruptedly.
>>
>> Signed-off-by: Roman Gushchin <klamm@yandex-team•ru>
>> Reported-by: Boris Zhmurov <zhmurov@yandex-team•ru>
>> ---
>> include/linux/rculist_nulls.h | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
>> index 2ae1371..efd51bf 100644
>> --- a/include/linux/rculist_nulls.h
>> +++ b/include/linux/rculist_nulls.h
>> @@ -37,8 +37,9 @@ static inline void hlist_nulls_del_init_rcu(struct
>> hlist_nulls_node *n)
>> }
>> }
>>
>> -#define hlist_nulls_first_rcu(head) \
>> - (*((struct hlist_nulls_node __rcu __force **)&(head)->first))
>> +#define hlist_nulls_first_rcu(head) \
>> + (*((struct hlist_nulls_node __rcu __force **) \
>> + &((volatile typeof(*head) *)head)->first))
>
> Why not use ACCESS_ONCE() or (better) rcu_dereference_raw() here?
It will be nice, but will require to keep the old variant too (for using
in hlist_nulls_add_head_rcu() as in rcu_assign_pointer() argument). Do
you think, it's better?
Regards,
Roman
next prev parent reply other threads:[~2013-05-21 12:46 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-21 9:05 [PATCH] rcu: fix a race in hlist_nulls_for_each_entry_rcu macro Roman Gushchin
2013-05-21 10:40 ` David Laight
2013-05-21 11:55 ` Roman Gushchin
2013-05-21 13:42 ` David Laight
2013-05-21 12:09 ` Paul E. McKenney
2013-05-21 12:46 ` Roman Gushchin [this message]
2013-05-21 12:58 ` Paul E. McKenney
2013-05-21 13:37 ` Eric Dumazet
2013-05-21 13:44 ` Eric Dumazet
2013-05-21 14:47 ` Roman Gushchin
2013-05-21 15:16 ` Eric Dumazet
2013-05-21 15:51 ` Roman Gushchin
2013-05-21 15:38 ` Eric Dumazet
2013-05-21 15:51 ` Roman Gushchin
2013-05-21 18:12 ` [PATCH v2] " Roman Gushchin
2013-05-22 2:01 ` Eric Dumazet
2013-05-22 5:49 ` Eric Dumazet
2013-05-22 11:58 ` Roman Gushchin
2013-05-22 12:30 ` Eric Dumazet
2013-05-22 13:07 ` Roman Gushchin
2013-05-22 17:45 ` Paul E. McKenney
2013-05-22 19:17 ` Roman Gushchin
2013-05-25 11:37 ` Paul E. McKenney
2013-05-27 11:34 ` Roman Gushchin
2013-05-27 17:55 ` Roman Gushchin
2013-05-28 0:12 ` Eric Dumazet
2013-05-28 9:10 ` Roman Gushchin
2013-05-29 0:34 ` Eric Dumazet
2013-05-29 1:31 ` Paul E. McKenney
2013-05-29 5:08 ` Eric Dumazet
2013-05-29 10:09 ` Roman Gushchin
2013-05-29 19:06 ` Eric Dumazet
2013-05-30 8:25 ` Roman Gushchin
2013-06-02 23:31 ` Eric Dumazet
2013-06-03 2:58 ` David Miller
2013-06-03 3:12 ` Eric Dumazet
2013-06-03 3:27 ` David Miller
2013-06-03 3:42 ` Paul E. McKenney
2013-06-03 3:47 ` Eric Dumazet
2013-06-03 3:49 ` David Miller
2013-06-03 6:05 ` Paul E. McKenney
2013-06-10 18:29 ` Boris B. Zhmurov
2013-06-10 18:51 ` Eric Dumazet
2013-06-03 3:48 ` Paul E. McKenney
2013-06-03 3:42 ` Paul E. McKenney
2013-05-29 9:17 ` Roman Gushchin
2013-05-29 1:19 ` Paul E. McKenney
2013-05-22 13:27 ` David Laight
2013-05-22 13:36 ` Eric Dumazet
2013-05-22 14:23 ` David Laight
2013-05-22 13:55 ` Roman Gushchin
2013-05-22 9:58 ` Paul E. McKenney
2013-05-22 12:28 ` Eric Dumazet
2013-05-22 13:00 ` Paul E. McKenney
2013-05-22 14:16 ` Eric Dumazet
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