From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stanislav Kinsbursky Subject: Re: [PATCH v4 1/8] SUNRPC: introduce helpers for reference counted rpcbind clients Date: Tue, 20 Sep 2011 19:03:37 +0400 Message-ID: <4E78AB49.1030303@parallels.com> References: <20110920101031.9861.18444.stgit@localhost6.localdomain6> <20110920101341.9861.51453.stgit@localhost6.localdomain6> <4E788F8C.20103@netapp.com> <2E1EB2CF9ED1CB4AA966F0EB76EAB4430B47FD10@SACMVEXC2-PRD.hq.netapp.com> <4E789679.1060601@parallels.com> <2E1EB2CF9ED1CB4AA966F0EB76EAB4430B47FD22@SACMVEXC2-PRD.hq.netapp.com> <4E78A4AF.1020303@parallels.com> <2E1EB2CF9ED1CB4AA966F0EB76EAB4430B47FD2B@SACMVEXC2-PRD.hq.netapp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE 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" To: "Myklebust, Trond" Return-path: In-Reply-To: <2E1EB2CF9ED1CB4AA966F0EB76EAB4430B47FD2B@SACMVEXC2-PRD.hq.netapp.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 20.09.2011 18:38, Myklebust, Trond =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> -----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 =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> >>>>> >>>>> 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=3D1? >>> >> >> 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 y= ou >> guarantee that rpcb_users !=3D 0 implies rpbc_local_clnt/4 !=3D NULL= ? >>> >> >> We check rpcb_users under spinlock. Gain spinlock forces memory barr= ier, >> 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). --=20 Best regards, Stanislav Kinsbursky