netdev - Re: [PATCH tip/core/rcu 05/13] net: add checking to rcu

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Message-ID: <e2d7436a1002140034h74617164p1a5dc90df3587095@mail.gmail.com>
Date:	Sun, 14 Feb 2010 09:34:43 +0100
From:	Michał Mirosław <mirqus@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH tip/core/rcu 05/13] net: add checking to rcu_dereference() 
	primitives

2010/2/12 Eric Dumazet <eric.dumazet@...il.com>:
> Le jeudi 11 février 2010 à 16:00 -0800, Paul E. McKenney a écrit :
[...]
>> @@ -1654,12 +1654,12 @@ static struct dn_route *dn_rt_cache_get_first(struct seq_file *seq)
>>
>>       for(s->bucket = dn_rt_hash_mask; s->bucket >= 0; --s->bucket) {
>>               rcu_read_lock_bh();
>> -             rt = dn_rt_hash_table[s->bucket].chain;
>> +             rt = rcu_dereference_bh(dn_rt_hash_table[s->bucket].chain);
>>               if (rt)
>>                       break;
>>               rcu_read_unlock_bh();
>>       }
>> -     return rcu_dereference(rt);
>> +     return rt;
>>  }

Isn't there a bug? Looks like data pointed to by rt should be
protected by RCU, but the rcu_read_lock is withdrawn before access.

Best Regards,
Michał Mirosław
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