From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760746Ab2CNXaC (ORCPT ); Wed, 14 Mar 2012 19:30:02 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:45497 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751546Ab2CNX36 (ORCPT ); Wed, 14 Mar 2012 19:29:58 -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 00:34:08 +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> <201203150013.45749.rjw@sisk.pl> <4F612706.4060407@codeaurora.org> In-Reply-To: <4F612706.4060407@codeaurora.org> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201203150034.08863.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 16:13, Rafael J. Wysocki wrote: > > On Thursday, March 15, 2012, Rafael J. Wysocki wrote: > >> On Wednesday, March 14, 2012, Stephen Boyd wrote: > >>> On 03/13/12 13:14, Rafael J. Wysocki wrote: > >>>> All of those use cases are in fact of the "wait for user space to be thawed > >>>> and then load the firmware" type, which I believe may be handled without > >>>> changing that code. > >>>> > >>>> Why don't you make your kthread freezable, for one example? > >>>> > >>>> Why don't you use a freezable workqueue instead? > >>>> > >>> If we put it on the freezable workqueue or make it a freezable thread > >>> will it work? > >> That depends on what exactly you want to achieve, which isn't entirely clear > >> to me at this point. > >> > >>> In my scenario a wakeup interrupt comes in that wakes us up from > >>> suspend. Within that wakeup handler a work item is scheduled to the > >>> freezable workqueue. That work item then calls request_firmware(). > >> That should work. > >> > >>> It looks like we call schedule() after thawing the workqueues and tasks > >>> so the work item could run before usermodehelpers are enabled and then > >>> request_firmware() would fail. Do we need something like this (ignore > >>> the fact that we call usermodhelper_enable() twice)? > >>> > >>> diff --git a/kernel/power/process.c b/kernel/power/process.c > >>> index 7e42645..61bfa95 100644 > >>> --- a/kernel/power/process.c > >>> +++ b/kernel/power/process.c > >>> @@ -187,6 +187,7 @@ void thaw_processes(void) > >>> } while_each_thread(g, p); > >>> read_unlock(&tasklist_lock); > >>> > >>> + usermodehelper_enable(); > >> That would be a reasonable change. > >> > >>> schedule(); > >>> printk("done.\n"); > >>> } > >>> > >>> > >>> Is there a reason we disable usermodehelpers if > >>> CONFIG_SUSPEND_FREEZER=n? > >> Not really, but CONFIG_SUSPEND_FREEZER=n can only work reliably in a > >> very limited set of cases, so I don't think it's even worth making the > >> general code depend on it. > >> > >> I'd actually prefer to remove CONFIG_SUSPEND_FREEZER altogether, > >> because it's not very useful nowadays (probably isn't useful at all). > >> > >>> Should we do this instead so that > >>> usermodehelpers are only disabled if we freeze userspace? Also what is > >>> that schedule() call in thaw_kernel_threads() for? It looks like we'll > >>> call schedule between kernel thread thawing and userspace thawing. > >> 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. Thanks, Rafael