linux-kernel - Re: [PATCH] PM: avoid 'autosleep' in shutdown progress

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Date:	Sat, 13 Jul 2013 13:56:32 +0200
From:	Pavel Machek <pavel@....cz>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>, shuox.liu@...el.com,
	linux-kernel@...r.kernel.org, len.brown@...el.com, rjw@...k.pl,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH] PM: avoid 'autosleep' in shutdown progress

On Fri 2013-07-12 10:37:33, Alan Stern wrote:
> On Fri, 12 Jul 2013, Yanmin Zhang wrote:
> 
> > On Thu, 2013-07-11 at 16:03 +0800, shuox.liu@...el.com wrote:
> > > From: Liu ShuoX <shuox.liu@...el.com>
> > > 
> > > In shutdown progress, system is possible to do power transition
> > > (such as suspend-to-ram) in parallel. It is unreasonable. So,
> > > fixes it by adding a system_state checking and queue try_to_suspend
> > > again when system status is not running.
> > > 
> > > Signed-off-by: Liu ShuoX <shuox.liu@...el.com>
> > > ---
> > >  kernel/power/autosleep.c |    3 ++-
> > >  1 files changed, 2 insertions(+), 1 deletions(-)
> > > 
> > Without this patch, we hit an hang issue on Android.
> > 
> > Scenario:
> > Kernel starts shutdown and calls all device driver's shutdown callback.
> > When a driver's shutdown is called, the last wakelock is released and
> > suspend-to-ram starts. However, as some driver's shut down callbacks
> > already shut down devices and disable runtime pm, the suspend-to-ram
> > calls driver's suspend callback without noticing that device is already
> > off and causes crash.
> > We know the drivers should be fixed, but can we also change generic
> > codes a little to make it stronger?
> 
> Indeed, this does seem like the sort of thing we want to have.  
> Allowing an "automatic" or "opportunistic" sleep in the middle of a
> shutdown makes no sense at all.  In fact, it might be a good idea to
> disable system sleep completely at this time -- not even a write to
> /sys/power/state should be allowed to interrupt a shutdown.

I'm not completely sure, but as long as userland is running, we should
have system_state == RUNNING, no?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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