From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751344AbVI2XbG (ORCPT ); Thu, 29 Sep 2005 19:31:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751366AbVI2XbG (ORCPT ); Thu, 29 Sep 2005 19:31:06 -0400 Received: from lead.cat.pdx.edu ([131.252.208.91]:47599 "EHLO lead.cat.pdx.edu") by vger.kernel.org with ESMTP id S1751344AbVI2XbF (ORCPT ); Thu, 29 Sep 2005 19:31:05 -0400 Date: Thu, 29 Sep 2005 16:30:28 -0700 (PDT) From: Suzanne Wood Message-Id: <200509292330.j8TNUSmH019572@rastaban.cs.pdx.edu> To: herbert@gondor.apana.org.au Cc: Robert.Olsson@data.slu.se, davem@davemloft.net, linux-kernel@vger.kernel.org, netdev@oss.sgi.com, paulmck@us.ibm.com, walpole@cs.pdx.edu Subject: Re: [RFC][PATCH] identify in_dev_get rcu read-side critical sections Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > Date: Fri, 30 Sep 2005 07:28:36 +1000 > From: Herbert Xu > On Thu, Sep 29, 2005 at 09:02:29AM -0700, Suzanne Wood wrote: > > > > The exchange below suggests that it is equally important > > to have the rcu_dereference() in __in_dev_get(), so the > > idea of the only difference between in_dev_get and > > __in_dev_get being the refcnt may be accepted. > With __in_dev_get() it's the caller's responsibility to ensure > that RCU works correctly. Therefore if any rcu_dereference is > needed it should be done by the caller. This sounds reasonable to me. Does everyone agree? > Some callers of __in_dev_get() don't need rcu_dereference at all > because they're protected by the rtnl. > BTW, could you please move the rcu_dereference in in_dev_get() > into the if clause? The barrier is not needed when ip_ptr is > NULL. The trouble with that may be that there are three events, the dereference, the assignment, and the conditional test. The rcu_dereference() is meant to assure deferred destruction throughout. Thank you very much for your suggestions.