From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031217Ab2CNXJj (ORCPT ); Wed, 14 Mar 2012 19:09:39 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:45437 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758999Ab2CNXJe (ORCPT ); Wed, 14 Mar 2012 19:09:34 -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 00:13:45 +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> <4F60EFBB.5050703@codeaurora.org> <201203150004.17076.rjw@sisk.pl> In-Reply-To: <201203150004.17076.rjw@sisk.pl> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201203150013.45749.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, 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). In all other cases, thaw_processes() is used to thaw kernel threads and user space at the same time, so I believe we don't need the changes you're proposing in that area. Thanks, Rafael