From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965714AbXDEJq6 (ORCPT ); Thu, 5 Apr 2007 05:46:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965927AbXDEJq6 (ORCPT ); Thu, 5 Apr 2007 05:46:58 -0400 Received: from mail.screens.ru ([213.234.233.54]:57491 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965714AbXDEJq5 (ORCPT ); Thu, 5 Apr 2007 05:46:57 -0400 Date: Thu, 5 Apr 2007 13:46:33 +0400 From: Oleg Nesterov To: Gautham R Shenoy Cc: akpm@linux-foundation.org, paulmck@us.ibm.com, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, vatsa@in.ibm.com, "Rafael J. Wysocki" , mingo@elte.hu, dipankar@in.ibm.com, dino@in.ibm.com, masami.hiramatsu.pt@hitachi.com Subject: Re: [PATCH 1/8] Enhance process freezer interface for usage beyond software suspend Message-ID: <20070405094633.GA609@tv-sign.ru> References: <20070402053457.GA9076@in.ibm.com> <20070402053705.GA12962@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070402053705.GA12962@in.ibm.com> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On 04/02, Gautham R Shenoy wrote: > > +/* > + * Exempt the current process from being frozen for a certain event > + */ > +static inline void freezer_exempt(unsigned long exempt_freeze_event) > +{ > + if (exempt_freeze_event == FE_NONE) > + current->flags &= ~PF_FE_ALL; > + else > + current->flags |= exempt_freeze_event; > +} So, a kernel_thread should call freezer_exempt(FE_XXX) somewhere at the beginning if it doesn't want to be considered as freezeable. But what if the freezing is already in progress? In that case freezer_exempt() should somehow clear TIF_FREEZE (if exempt_freeze_event doesn't match freeze_event parameter of freeze_processes()), otherwise we may hit a nasty bug, much worse than a freezing failure (which could be restarted). try_to_freeze_tasks() succeeds because the task is !freezeable(), the task goes to refrigerator (while it should not), thaw_tasks() ignores process and it stays frozen. Alternatively, we can do a re-check in refrigerator() to fix this race. In any case, it looks like freeze_event should be stored in a global var. > --- linux-2.6.21-rc5.orig/kernel/sched.c > +++ linux-2.6.21-rc5/kernel/sched.c > @@ -5057,6 +5057,7 @@ static int migration_thread(void *data) > BUG_ON(rq->migration_thread != current); > > set_current_state(TASK_INTERRUPTIBLE); > + freezer_exempt(FE_ALL); This is a real nitpick, but it was hard to me to understand this change. Because it looks as if we have a subtle reason to set TASK_INTERRUPTIBLE before freezer_exempt(). Unless I missed something, I'd suggest to move freezer_exempt() up, before set_current_state(). The same for apm_mainloop(). Oleg.