linux-kernel - Re: [PATCH v2] PM / sleep: prohibit devices probing during suspend/hibernation

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Message-ID: <20151106000957.GB10347@kroah.com>
Date:	Thu, 5 Nov 2015 16:09:57 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Grygorii Strashko <grygorii.strashko@...com>,
	stern@...land.harvard.edu, linux-pm@...r.kernel.org,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	linux-kernel@...r.kernel.org,
	Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH v2] PM / sleep: prohibit devices probing during
 suspend/hibernation

On Thu, Nov 05, 2015 at 11:38:23PM +0100, Rafael J. Wysocki wrote:
> On Monday, November 02, 2015 02:25:00 AM Rafael J. Wysocki wrote:
> > On Monday, October 19, 2015 11:54:24 PM Grygorii Strashko wrote:
> > > It is unsafe [1] if probing of devices will happen during suspend or
> > > hibernation and system behavior will be unpredictable in this case
> > > (for example: after successful probe the device potentially has a different
> > >  set of PM callbacks than before [2]).
> > > So, let's prohibit device's probing in dpm_prepare() and defer their
> > > probes instead. The normal behavior will be restored in dpm_complete().
> > > 
> > > This patch introduces new DD core APIs:
> > >  device_defer_all_probes_enable()
> > >    It will disable probing of devices and defer their probes.
> > >  device_defer_all_probes_disable()
> > >    It will restore normal behavior and trigger re-probing of deferred
> > >    devices.
> > > 
> > > [1] https://lkml.org/lkml/2015/9/11/554
> > > [2] https://lkml.org/lkml/2015/9/15/1039
> > > Cc: Alan Stern <stern@...land.harvard.edu>
> > > Cc: Rafael J. Wysocki <rjw@...ysocki.net>
> > > Cc: Thierry Reding <thierry.reding@...il.com>
> > > Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> > 
> > Greg, any objections against this one?
> 
> Greg, if this isn't problematic, I'd still like to take it for v4.4.

What?  The merge window for new stuff closed a few weeks ago, how can
you add this for 4.4 when it needs to be in linux-next for a while
first?

I don't have any real objection to it, but I don't see how defering
probing until "later" really solves anything, no one should be "changing
pm callbacks" after some other probe succeeds, that sounds like someone
just wants to have a broken system.

thanks,

greg k-h
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