From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:57256 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753044AbeD3Nlz (ORCPT ); Mon, 30 Apr 2018 09:41:55 -0400 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w3UDfE9r034802 for ; Mon, 30 Apr 2018 09:41:54 -0400 Received: from e14.ny.us.ibm.com (e14.ny.us.ibm.com [129.33.205.204]) by mx0a-001b2d01.pphosted.com with ESMTP id 2hp1vsxvmf-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 30 Apr 2018 09:41:54 -0400 Received: from localhost by e14.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 30 Apr 2018 09:41:53 -0400 Date: Mon, 30 Apr 2018 06:43:08 -0700 From: "Paul E. McKenney" To: Josh Triplett Cc: NeilBrown , Trond Myklebust , Mathieu Desnoyers , Anna Schumaker , linux-nfs@vger.kernel.org, Lai Jiangshan , Steven Rostedt , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/4] rculist: add list_for_each_entry_from_rcu() Reply-To: paulmck@linux.vnet.ibm.com References: <152506256513.7246.13171564155614823841.stgit@noble> <152506269061.7246.13075216914692813995.stgit@noble> <20180430052032.GA16963@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180430052032.GA16963@localhost> Message-Id: <20180430134308.GT26088@linux.vnet.ibm.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Sun, Apr 29, 2018 at 10:20:33PM -0700, Josh Triplett wrote: > On Mon, Apr 30, 2018 at 02:31:30PM +1000, NeilBrown wrote: > > list_for_each_entry_from_rcu() is an RCU version of > > list_for_each_entry_from(). It walks a linked list under rcu > > protection, from a given start point. > > > > It is similar to list_for_each_entry_continue_rcu() but starts *at* > > the given position rather than *after* it. > > > > Naturally, the start point must be known to be in the list. > > I'd suggest giving an explicit advisory comment to clarify and suggest > correct usage: > > "This would typically require either that you obtained the node from a > previous walk of the list in the same RCU read-side critical section, or > that you held some sort of non-RCU reference (such as a reference count) > to keep the node alive *and* in the list." > > (Feel free to wordsmith the exact wording, but something like that seems > like it would help people understand how to use this correctly, and make > it less likely that they'd use it incorrectly.) What Josh said! Could you also contrast this with the existing list_for_each_entry_continue_rcu() macro in the header comment as well as in the commit log? Thanx, Paul