From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-nfs-owner@vger.kernel.org>
Received: from mail.kernel.org ([198.145.29.99]:37140 "EHLO mail.kernel.org"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1752255AbeD3PO5 (ORCPT <rfc822;linux-nfs@vger.kernel.org>);
        Mon, 30 Apr 2018 11:14:57 -0400
Date: Mon, 30 Apr 2018 11:14:54 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>, NeilBrown <neilb@suse.com>,
        Trond Myklebust <trond.myklebust@primarydata.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Anna Schumaker <anna.schumaker@netapp.com>,
        linux-nfs@vger.kernel.org, Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/4] rculist: add list_for_each_entry_from_rcu()
Message-ID: <20180430111454.722c2aa8@gandalf.local.home>
In-Reply-To: <20180430134308.GT26088@linux.vnet.ibm.com>
References: <152506256513.7246.13171564155614823841.stgit@noble>
        <152506269061.7246.13075216914692813995.stgit@noble>
        <20180430052032.GA16963@localhost>
        <20180430134308.GT26088@linux.vnet.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-nfs-owner@vger.kernel.org
List-ID: <linux-nfs.vger.kernel.org>

On Mon, 30 Apr 2018 06:43:08 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> 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?
> 

Should Documentation/RCU/whatisRCU.txt be updated?

Specifically section: 7.  FULL LIST OF RCU APIs

-- Steve