From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031323Ab2COAHF (ORCPT ); Wed, 14 Mar 2012 20:07:05 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:45613 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031223Ab2COAHB (ORCPT ); Wed, 14 Mar 2012 20:07:01 -0400 From: "Rafael J. Wysocki" To: Stephen Boyd Subject: Re: [PATCH] firmware loader: don't cancel _nowait requests when helper is not yet available Date: Thu, 15 Mar 2012 01:11:05 +0100 User-Agent: KMail/1.13.6 (Linux/3.3.0-rc7+; KDE/4.6.0; x86_64; ; ) Cc: Saravana Kannan , Kay Sievers , Greg KH , Christian Lamparter , linux-kernel@vger.kernel.org, "Srivatsa S. Bhat" , alan@lxorguk.ukuu.org.uk, Linus Torvalds , Linux PM mailing list References: <201203032122.36745.chunkeey@googlemail.com> <201203150034.08863.rjw@sisk.pl> <4F612C05.8010301@codeaurora.org> In-Reply-To: <4F612C05.8010301@codeaurora.org> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201203150111.05724.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday, March 15, 2012, Stephen Boyd wrote: > On 03/14/12 16:34, Rafael J. Wysocki wrote: > > On Thursday, March 15, 2012, Stephen Boyd wrote: > >> On 03/14/12 16:13, Rafael J. Wysocki wrote: > >>> On Thursday, March 15, 2012, Rafael J. Wysocki wrote: > >>> > >>>> Which is OK, I think. > >>> Moreover, thaw_kernel_threads() is _only_ called by (a) freeze_kernel_threads() > >>> on error and (b) user-space hibernate interface in kernel/power/user.c > >>> (and please read the comment in there describing what it's there for, which > >>> also explains why the schedule() call in there is necessary). > >> Exactly. So in case (a) when the error occurs we'll have this call flow: > >> > >> usermodehelpers_disable() > >> suspend_freeze_processes() > >> freeze_processes() > >> freeze_kernel_threads() > >> try_to_freeze_tasks() <-- returns error > >> thaw_kernel_threads() > >> schedule() > >> thaw_processes() > >> usermodehelpers_enable() > >> > >> Shouldn't we schedule only after we thaw all processes (not just tasks)? > >> Otherwise we may run a kernel thread before userspace is thawed? > > Yes, we may, but that isn't wrong, is it? > > > > Only a few kernel threads are freezable, so definitely kernel threads > > can run while user space is frozen. > > > > Yes but if someone calls request_firmware() from a kthread then they > will hit the same problem where the thread runs and requests the > firmware and usermodehelpers are still disabled. Currently my code is > written with kthreads and that thread makes the request firmware call, > so this doesn't seem far fetched (although in my case I can probably fix > it). So again, please consider using suspend/resume notifiers to synchronize your kthread with system power transitions. > It looks like before 379e0be (PM / Freezer: Thaw only kernel > threads if freezing of kernel threads fails, 2012-02-03) schedule wasn't > called until userspace was thawed. It looks like that patch was about > hibernation and not suspend? It was about hibernation and it fixed a real bug. Thanks, Rafael