From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760641AbXGEJSR (ORCPT ); Thu, 5 Jul 2007 05:18:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758876AbXGEJSH (ORCPT ); Thu, 5 Jul 2007 05:18:07 -0400 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:57254 "EHLO amd.ucw.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758811AbXGEJSE (ORCPT ); Thu, 5 Jul 2007 05:18:04 -0400 Date: Thu, 5 Jul 2007 11:18:01 +0200 From: Pavel Machek To: Miklos Szeredi Cc: oliver@neukum.org, paulus@samba.org, stern@rowland.harvard.edu, johannes@sipsolutions.net, rjw@sisk.pl, linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, mjg59@srcf.ucam.org, benh@kernel.crashing.org Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway Message-ID: <20070705091801.GB3084@elf.ucw.cz> References: <18059.10554.955290.148535@cargo.ozlabs.ibm.com> <18060.14856.824473.325660@cargo.ozlabs.ibm.com> <200707050858.03638.oliver@neukum.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 On Thu 2007-07-05 10:17:17, Miklos Szeredi wrote: > > > > I have discussed the benefits elsewhere.  As for the deadlocks -- do > > > > you still observe them if you use the version of the freezer which > > > > doesn't freeze kernel threads? > > > > > > In general the only way to guarantee there are no deadlocks is to > > > construct the graph of dependencies between tasks.  Those dependencies > > > are not in practice observable from outside the tasks, so it is > > > virtually impossible to construct the graph. > > > > In which way can user space tasks depend on each other in a way that > > allows a them members of that cycle to be in uninterruptible sleep? > > - process A calls rename() on a fuse fs > - process B, the fuse server, starts to process the rename request > - process B is frozen before it can reply > > Now process A is unfreezable. We cannot make rename() restartable, > hence it cannot be interruptible. Yes, we are claiming fuse is very special in this regard, and perhaps even broken. Let's see. If I SIGSTOP the fuse server, I can get unrelated tasks unkillable (even for SIGKILL!) forever. That's very special, and maybe even a FUSE bug. And that is also what makes FUSE special w.r.t. s2ram. So no, you can't claim "FUSE is just IPC". It is very special IPC. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html