From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754001AbXJ3ILO (ORCPT ); Tue, 30 Oct 2007 04:11:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753256AbXJ3ILB (ORCPT ); Tue, 30 Oct 2007 04:11:01 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:34717 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752267AbXJ3IK6 (ORCPT ); Tue, 30 Oct 2007 04:10:58 -0400 Date: Tue, 30 Oct 2007 01:10:36 -0700 (PDT) Message-Id: <20071030.011036.43329108.davem@davemloft.net> To: paulmck@linux.vnet.ibm.com Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, SteveW@ACM.org, dipankar@in.ibm.com Subject: Re: dn_route.c momentarily exiting RCU read-side critical section From: David Miller In-Reply-To: <20071029211540.GA12893@linux.vnet.ibm.com> References: <20071029211540.GA12893@linux.vnet.ibm.com> X-Mailer: Mew version 5.2 on Emacs 22.1 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Date: Mon, 29 Oct 2007 14:15:40 -0700 > net/decnet/dn_route.c in dn_rt_cache_get_next() is as follows: > > static struct dn_route *dn_rt_cache_get_next(struct seq_file *seq, struct dn_route *rt) > { > struct dn_rt_cache_iter_state *s = rcu_dereference(seq->private); > > rt = rt->u.dst.dn_next; > while(!rt) { > rcu_read_unlock_bh(); > if (--s->bucket < 0) > break; > > ... But what happens if seq->private is freed up right here? > ... Or what prevents this from happening? ... > Similar code is in rt_cache_get_next(). > > So, what am I missing here? seq->private is allocated on file open (here via seq_open_private()), and freed up on file close (via seq_release_private). So it cannot be freed up in the middle of an iteration.