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

[Stanislav Kinsbursky]

20.09.2011 18:38, Myklebust, Trond ÐÐÑÐÑ:
> > -----Original Message-----
> > From: Stanislav Kinsbursky [mailto:skinsbursky@xxxxxxxxxxxxx]
> > Sent: Tuesday, September 20, 2011 10:35 AM
> > To: Myklebust, Trond
> > Cc: Schumaker, Bryan; linux-nfs@xxxxxxxxxxxxxxx; Pavel Emelianov;
> > neilb@xxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > bfields@xxxxxxxxxxxx; davem@xxxxxxxxxxxxx
> > Subject: Re: [PATCH v4 1/8] SUNRPC: introduce helpers for reference
> > counted rpcbind clients
> >
> > 20.09.2011 18:14, Myklebust, Trond ÐÐÑÐÑ:
> >
> > > > > 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
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