Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946444AbXBCLHR (ORCPT ); Sat, 3 Feb 2007 06:07:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1946448AbXBCLHR (ORCPT ); Sat, 3 Feb 2007 06:07:17 -0500 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:46704 "EHLO amd.ucw.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1946444AbXBCLHP (ORCPT ); Sat, 3 Feb 2007 06:07:15 -0500 Date: Sat, 3 Feb 2007 01:01:53 +0100 From: Pavel Machek To: "Rafael J. Wysocki" Cc: paulmck@linux.vnet.ibm.com, Ingo Molnar , Andrew Morton , dipankar@in.ibm.com, Gautham Shenoy , linux-kernel@vger.kernel.org Subject: Re: Fw: Re: [mm PATCH 4/6] RCU: (now) CPU hotplug Message-ID: <20070203000153.GA1712@elf.ucw.cz> References: <20070126112837.059502fc.akpm@osdl.org> <20070130073340.GC30160@elte.hu> <20070130160244.GB2092@linux.vnet.ibm.com> <200701301744.48601.rjw@sisk.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200701301744.48601.rjw@sisk.pl> X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.11+cvs20060126 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1783 Lines: 50 Hi! > > > > static int _cpu_down(unsigned int cpu) > > > > { > > > > int err; > > > > struct task_struct *p; > > > > cpumask_t old_allowed, tmp; > > > > > > > > if (num_online_cpus() == 1) > > > > return -EBUSY; > > > > > > > > if (!cpu_online(cpu)) > > > > return -EINVAL; > > > > > > > > if (freeze_processes()) { > > > > err = -EBUSY; > > > > goto out_freeze_notify_failed; > > > > } > > > > err = raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE, > > > > (void *)(long)cpu); > > > > > > yeah. This all looks so nice that i almost cannot believe it's true :-) > > > > Well, it turns out that maybe it is in fact untrue. :-/ > > > > I need to look at all uses of PF_NOFREEZE -- as I understand the > > code, processes marked PF_NOFREEZE will continue running, potentially > > interfering with the hotplug operation. :-( > > > > I will pass my findings on to this list. > > Well, I did it some time ago, although not very thoroughly. > > AFAICS there are not so many, but one that stands out is the worker threads. > We needed two of them to actually go to sleep, so now it's possible to create > a "freezeable workqueue" the worker thread of which will not set PF_NOFREEZE, > but currently this is only used by XFS. We should slowly move as workqueues to freezeable ones... Having too much stuff NOFREEZE is evil, even for swsusp. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/