Re: [PATCH v4 1/8] SUNRPC: introduce helpers for reference counted rpcbind clients

[Stanislav Kinsbursky <skinsbursky@parallels.com>]

20.09.2011 18:38, Myklebust, Trond пишет:
>> -----Original Message-----
>> From: Stanislav Kinsbursky [mailto:skinsbursky@parallels.com]
>> Sent: Tuesday, September 20, 2011 10:35 AM
>> To: Myklebust, Trond
>> Cc: Schumaker, Bryan; linux-nfs@vger.kernel.org; Pavel Emelianov;
>> neilb@suse.de; netdev@vger.kernel.org; linux-kernel@vger.kernel.org;
>> bfields@fieldses.org; davem@davemloft.net
>> Subject: Re: [PATCH v4 1/8] SUNRPC: introduce helpers for reference
>> counted rpcbind clients
>>
>> 20.09.2011 18:14, Myklebust, Trond пишет:
>>
>>>>>
>>>>> Doesn't it  need to be protected by rpcb_clnt_lock too?
>>>>>
>>>>
>>>> Nope from my pow. It's protected by rpcb_create_local_mutex. I.e. no
>>>> one will change rpcb_users since it's zero. If it's non zero - we
>>>> willn't get to rpcb_set_local().
>>>
>>> OK, so you are saying that the rpcb_users++ below could be replaced by
>> rpcb_users=1?
>>>
>>
>> Yes, you right.
>>
>>> In that case, don't you need a smp_wmb() between the setting of
>> rpcb_local_clnt/4 and the setting of rpcb_users? Otherwise, how do you
>> guarantee that rpcb_users != 0 implies rpbc_local_clnt/4 != NULL?
>>>
>>
>> We check rpcb_users under spinlock. Gain spinlock forces memory barrier,
>> doesn't it?
>
> Yes, and so you don't need an smp_rmb() on the reader side. However, you still need to ensure that the processor which _sets_ the rpcb_users and rpcb_local_clnt/4 actually writes them in the correct order.
>

Yep, now I understand what are you talking about.
Will fix both places (set and put).

-- 
Best regards,
Stanislav Kinsbursky