From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757232Ab0IBVcI (ORCPT ); Thu, 2 Sep 2010 17:32:08 -0400 Received: from smtp-out.google.com ([216.239.44.51]:57821 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754305Ab0IBVcF convert rfc822-to-8bit (ORCPT ); Thu, 2 Sep 2010 17:32:05 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=e9gC5YURQ+dp5aon66jOEw1v/qyvLe6WNQre79JN/I7+6g1xzP9VizZY5j3BeZCoCS We0zrezzpZIK0W6EZtPA== MIME-Version: 1.0 In-Reply-To: <201009022305.09187.rjw@sisk.pl> References: <201009022146.03359.rjw@sisk.pl> <201009022305.09187.rjw@sisk.pl> Date: Thu, 2 Sep 2010 14:31:55 -0700 X-Google-Sender-Auth: hcGbpE4j2h1eQbWzyIDT8c_Z6e8 Message-ID: Subject: Re: [PATCH] PM: Prevent waiting forever on asynchronous resume after abort From: Colin Cross To: "Rafael J. Wysocki" Cc: Alan Stern , linux-kernel@vger.kernel.org, linux-pm@lists.linux-foundation.org, Pavel Machek , Len Brown , Greg Kroah-Hartman , Randy Dunlap , Andrew Morton Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 2, 2010 at 2:05 PM, Rafael J. Wysocki wrote: > On Thursday, September 02, 2010, Colin Cross wrote: >> On Thu, Sep 2, 2010 at 12:46 PM, Rafael J. Wysocki wrote: >> > On Thursday, September 02, 2010, Alan Stern wrote: >> >> On Wed, 1 Sep 2010, Colin Cross wrote: >> >> >> >> > Only wait on a parent device during resume if the parent device is >> >> > suspended. >> >> > >> >> > Consider three drivers, A, B, and C.  The parent of A is C, and C >> >> > has async_suspend set.  On boot, C->power.completion is initialized >> >> > to 0. >> >> > >> >> > During the first suspend: >> >> > suspend_devices_and_enter(...) >> >> >  dpm_resume(...) >> >> >   device_suspend(A) >> >> >   device_suspend(B) returns error, aborts suspend >> >> >  dpm_resume_end(...) >> >> >    dpm_resume(...) >> >> >     device_resume(A) >> >> >      dpm_wait(A->parent == C) >> >> >       wait_for_completion(C->power.completion) >> >> > >> >> > The wait_for_completion will never complete, because >> >> > complete_all(C->power.completion) will only be called from >> >> > device_suspend(C) or device_resume(C), neither of which is called >> >> > if suspend is aborted before C. >> >> >> >> This would work okay if C->power.completion had been initialized to the >> >> completed state during boot, right? >> >> >> >> > After a successful suspend->resume cycle, where B doesn't abort >> >> > suspend, C->power.completion is left in the completed state by the >> >> > call to device_resume(C), and the same call path will work if B >> >> > aborts suspend. >> >> > >> >> > Signed-off-by: Colin Cross >> >> > --- >> >> >  drivers/base/power/main.c |    3 ++- >> >> >  1 files changed, 2 insertions(+), 1 deletions(-) >> >> > >> >> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c >> >> > index cb784a0..e159910 100644 >> >> > --- a/drivers/base/power/main.c >> >> > +++ b/drivers/base/power/main.c >> >> > @@ -526,7 +526,8 @@ static int device_resume(struct device *dev, pm_message_t state, bool async) >> >> >     TRACE_DEVICE(dev); >> >> >     TRACE_RESUME(0); >> >> > >> >> > -   dpm_wait(dev->parent, async); >> >> > +   if (dev->parent && dev->parent->power.status >= DPM_OFF) >> >> > +           dpm_wait(dev->parent, async); >> >> >     device_lock(dev); >> >> > >> >> >     dev->power.status = DPM_RESUMING; >> >> >> >> I think it would be better to change device_pm_init() and add a >> >> complete_all(). >> > >> > I agree. >> That would work, and was my first solution, but it increases the >> reliance on the completion variable being left completed between state >> transitions, which is undocumented and unnecessary. > > In fact it is necessary, because dpm_wait() may be called by external code > through device_pm_wait_for_dev() which is exported for a reason.  That may > lead to problems analogous to the one you described if the completion > variables are not completed initially. > >> It seems more straightforward to me to only wait on the parent if the parent is >> suspended. >> >> > Who's writing the patch? >> I'll write it if you still don't like this one. > > Yes, please. OK - do you prefer it in dpm_prepare or device_pm_init?