linux-kernel - Re: Change behaviour when tracing ... nasty trap (was Re: [PATCH] PM/Trace: get rid of synchronous resume limit during PM trace)

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Date:	Mon, 26 Jan 2015 14:41:02 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Pavel Machek <pavel@....cz>
Cc:	"Liu, Chuansheng" <chuansheng.liu@...el.com>,
	"Fu, Zhonghui" <zhonghui.fu@...ux.intel.com>,
	"Brown, Len" <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Change behaviour when tracing ... nasty trap (was Re: [PATCH] PM/Trace: get rid of synchronous resume limit during PM trace)

On Monday, January 26, 2015 12:05:16 PM Pavel Machek wrote:
> On Mon 2015-01-26 10:39:04, Liu, Chuansheng wrote:
> > Hello Pavel,
> > 
> > > > There are some kind of dependency between devices in some
> > > > hardware platforms. So, asynchronous resuming devices may
> > > > hang system due to wrong resume order. As a result, should
> > > > not fore synchronously resuming devices during tracing
> > > > PM events.
> > > >
> > > > Signed-off-by: Zhonghui Fu <zhonghui.fu@...ux.intel.com>
> > > > ---
> > > >  drivers/base/power/main.c    |    3 +--
> > > >  include/linux/resume-trace.h |    7 -------
> > > >  2 files changed, 1 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > > > index 9717d5f..5df148b 100644
> > > > --- a/drivers/base/power/main.c
> > > > +++ b/drivers/base/power/main.c
> > > > @@ -517,8 +517,7 @@ static int device_resume_noirq(struct device *dev,
> > > pm_message_t state, bool asyn
> > > >
> > > >  static bool is_async(struct device *dev)
> > > >  {
> > > > -	return dev->power.async_suspend && pm_async_enabled
> > > > -		&& !pm_trace_is_enabled();
> > > > +	return dev->power.async_suspend && pm_async_enabled;
> > > >  }
> > > >
> > > 
> > > Actually... whoever did the original patch was evil person. Changing
> > > behaviour when tracing is requested is evil, evil, evil. Git blame
> > > tells me
> > > 
> > > Signed-off-by: Chuansheng Liu <chuansheng.liu@...el.com>
> > > 
> > > went to the dark side.
> > 
> > Although I didn't get where is something wrong, but the is_async() is not created by my commit,
> > it is from commit (PM: Start asynchronous resume threads upfront), I just moved it ahead.
> > 
> > And like other phases, I added it into resum/suspend_noirq()...
> 
> I see, blame blamed wrong person. It looks like Rafael is evil:
> 
> commit 97df8c12995c5bac73e3bfeea4c5be155c1f4401
> Author: Rafael J. Wysocki <rjw@...k.pl>
> Date:   Sat Jan 23 22:25:31 2010 +0100
> 
>     PM: Start asynchronous resume threads upfront

This only means we won't use asyc suspend/resume at all when the RTC-based
resume debug is enabled, because it wouldn't make sense (the RTC-based
debug requires strict ordering of callbacks between devices or we may find
that device A hanged the resume while actually device B that was running in
parallel with A did that).

And I shouldn't even need to explain this ...  Sad.

Rafael

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