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

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Date:	Fri, 12 Jul 2013 10:37:33 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
cc:	shuox.liu@...el.com, <linux-kernel@...r.kernel.org>,
	<len.brown@...el.com>, <pavel@....cz>, <rjw@...k.pl>,
	<linux-pm@...r.kernel.org>
Subject: Re: [PATCH] PM: avoid 'autosleep' in shutdown progress

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.

Alan Stern

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