From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751578AbWFUNXN (ORCPT ); Wed, 21 Jun 2006 09:23:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751580AbWFUNXN (ORCPT ); Wed, 21 Jun 2006 09:23:13 -0400 Received: from omta01sl.mx.bigpond.com ([144.140.92.153]:37799 "EHLO omta01sl.mx.bigpond.com") by vger.kernel.org with ESMTP id S1751578AbWFUNXM (ORCPT ); Wed, 21 Jun 2006 09:23:12 -0400 Message-ID: <4499483D.3010509@bigpond.net.au> Date: Wed, 21 Jun 2006 23:23:09 +1000 From: Peter Williams User-Agent: Thunderbird 1.5.0.4 (X11/20060614) MIME-Version: 1.0 To: Peter Williams CC: Matt Helsley , Andrew Morton , nagar@watson.ibm.com, sekharan@us.ibm.com, jtk@us.ibm.com, balbir@in.ibm.com, jes@sgi.com, linux-kernel@vger.kernel.org, stern@rowland.harvard.edu, lse-tech@lists.sourceforge.net Subject: Re: [Lse-tech] [PATCH 09/11] Task watchers: Add support for per-task watchers References: <20060613235122.130021000@localhost.localdomain> <1150242901.21787.149.camel@stark> <44978793.8070109@bigpond.net.au> <1150844177.21787.774.camel@stark> <20060620161524.7c132eea.akpm@osdl.org> <1150852848.21787.828.camel@stark> <20060620184617.7dbefed8.akpm@osdl.org> <4498A728.207@bigpond.net.au> <44994311.5030707@bigpond.net.au> In-Reply-To: <44994311.5030707@bigpond.net.au> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Authentication-Info: Submitted using SMTP AUTH PLAIN at omta01sl.mx.bigpond.com from [147.10.133.38] using ID pwil3058@bigpond.net.au at Wed, 21 Jun 2006 13:23:10 +0000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Peter Williams wrote: > Peter Williams wrote: >> Andrew Morton wrote: >>> On Tue, 20 Jun 2006 18:20:48 -0700 >>> Matt Helsley wrote: >>> >>>>>>>> +static inline int notify_per_task_watchers(unsigned int val, >>>>>>>> + struct task_struct *task) >>>>>>>> +{ >>>>>>>> + if (get_watch_event(val) != WATCH_TASK_INIT) >>>>>>>> + return raw_notifier_call_chain(&task->notify, val, task); >>>>>>>> + RAW_INIT_NOTIFIER_HEAD(&task->notify); >>>>>>>> + if (task->real_parent) >>>>>>>> + return raw_notifier_call_chain(&task->real_parent->notify, >>>>>>>> + val, task); >>>>>>>> +} >>>>>>> It's possible for this task to exit without returning a result. >>>>>> Assuming you meant s/task/function/: >>>>>> >>>>>> In the common case this will return a result because most >>>>>> tasks have a >>>>>> real parent. The only exception should be the init task. However, the >>>>>> init task does not "fork" from another task so this function will >>>>>> never >>>>>> get called with WATCH_TASK_INIT and the init task. >>>>>> >>>>>> This means that if one wants to use per-task watchers to >>>>>> associate data >>>>>> and a function call with *every* task, special care will need to be >>>>>> taken to register with the init task. >>>>> no...... >>>> I've been looking through the source and, from what I can see, >>>> the end >>>> of the function is not reachable. I think I need to add: >>>> >>>> notify_watchers(WATCH_TASK_INIT, &init_task); >>>> >>>> to make this into an applicable warning. >>> >>> If the end of the function isn't reachable then the >>> `if (task->real_parent)' can simply be removed. >> >> Perhaps with a comment to say that it's safe (and why) to dereference >> task->real_parent to help code reviewers? > > Now that I understand this code better, I'm at a loss to understand why > you're calling the parent with the notifier. I can't think of any > circumstances where this would be useful. I spoke to soon and can now see how I can use this functionality. If I register my per task watcher with init_task, this functionality will allow me to do away with the normal watcher. Sorry for doubting, Peter -- Peter Williams pwil3058@bigpond.net.au "Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce