From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763254AbXGFHIr (ORCPT ); Fri, 6 Jul 2007 03:08:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763095AbXGFHIi (ORCPT ); Fri, 6 Jul 2007 03:08:38 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:56926 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763091AbXGFHIh convert rfc822-to-8bit (ORCPT ); Fri, 6 Jul 2007 03:08:37 -0400 From: "Rafael J. Wysocki" To: Pavel Machek Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway Date: Fri, 6 Jul 2007 09:16:15 +0200 User-Agent: KMail/1.9.5 Cc: Miklos Szeredi , oliver@neukum.org, paulus@samba.org, stern@rowland.harvard.edu, johannes@sipsolutions.net, linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, mjg59@srcf.ucam.org, benh@kernel.crashing.org References: <18059.10554.955290.148535@cargo.ozlabs.ibm.com> <20070705220444.GD3881@elf.ucw.cz> In-Reply-To: <20070705220444.GD3881@elf.ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8BIT Content-Disposition: inline Message-Id: <200707060916.16368.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Friday, 6 July 2007 00:04, Pavel Machek wrote: > Hi! > > > > > > > > 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. > > > > Actually fuse allows SIGKILL, because it's always fatal, and the > > syscall may not be restarted. > > Okay, and you should handle refrigerator in the same paths where you > handle SIGKILL. Just add try_to_freeze() there... In fact the problem is more complicated than that, because some tasks may be waiting on VFS locks related to FUSE. Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth