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

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Message-ID: <3237315.NCBdGinISd@vostro.rjw.lan>
Date:	Fri, 06 Nov 2015 01:13:35 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Pavel Machek <pavel@....cz>,
	Grygorii Strashko <grygorii.strashko@...com>
Cc:	stern@...land.harvard.edu,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pm@...r.kernel.org, Len Brown <len.brown@...el.com>,
	linux-kernel@...r.kernel.org,
	Thierry Reding <thierry.reding@...il.com>
Subject: Re: [PATCH v2] PM / sleep: prohibit devices probing during suspend/hibernation

On Thursday, November 05, 2015 11:19:03 PM Pavel Machek wrote:
> On Mon 2015-10-19 23:54:24, 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>
> > ---
> > Changes in v2:
> > - DD core API device_defer_all_probes(bool enable) split on two
> >   void device_defer_all_probes_enable(void);
> >   void device_defer_all_probes_disable(void);
> > - more comments added
> > 
> > Link on v1:
> > - https://lkml.org/lkml/2015/10/8/681
> > 
> >  drivers/base/base.h       |  2 ++
> >  drivers/base/dd.c         | 48 ++++++++++++++++++++++++++++++++++++++++++++++-
> >  drivers/base/power/main.c | 17 +++++++++++++++++
> >  3 files changed, 66 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/base/base.h b/drivers/base/base.h
> > index 1782f3a..c332b68 100644
> > --- a/drivers/base/base.h
> > +++ b/drivers/base/base.h
> > @@ -131,6 +131,8 @@ extern void device_remove_groups(struct device *dev,
> >  extern char *make_class_name(const char *name, struct kobject *kobj);
> >  
> >  extern int devres_release_all(struct device *dev);
> > +extern void device_defer_all_probes_enable(void);
> > +extern void device_defer_all_probes_disable(void);
> >  
> >  /* /sys/devices directory */
> >  extern struct kset *devices_kset;
> > diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> > index be0eb46..b8d9e70 100644
> > --- a/drivers/base/dd.c
> > +++ b/drivers/base/dd.c
> > @@ -55,6 +55,13 @@ static struct workqueue_struct *deferred_wq;
> >  static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
> >  
> >  /*
> > + * In some cases, like suspend to RAM or hibernation, It might be reasonable
> > + * to prohibit probing of devices as it could be unsafe.
> > + * Once defer_all_probes is true all drivers probes will be forcibly deferred.
> > + */
> > +static bool defer_all_probes;
> > +
> > +/*
> >   * deferred_probe_work_func() - Retry probing devices in the active list.
> >   */
> >  static void deferred_probe_work_func(struct work_struct *work)
> > @@ -172,6 +179,30 @@ static void driver_deferred_probe_trigger(void)
> >  }
> >  
> >  /**
> > + * device_defer_all_probes_enable() - Enable deferring of device's probes
> > + *
> > + *	It will disable probing of devices and defer their probes.
> > + */
> > +void device_defer_all_probes_enable(void)
> > +{
> > +	defer_all_probes = true;
> > +	/* sync with probes to avoid races. */
> > +	wait_for_device_probe();
> > +}
> 
> device_pause_probing()?
> 
> > +/**
> > + * device_defer_all_probes_disable() - Disable deferring of device's probes
> > + *
> > + *	It will restore normal behavior and trigger re-probing of deferred
> > + * devices.
> > + */
> 
> Hmm. This is not quite a double negative... but it sounds like one.
> 
> device_restart_probing()?

I _start/_stop would be fine by me too.

Thanks,
Rafael

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