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

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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@rowland.harvard.edu>
> > Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> > Cc: Thierry Reding <thierry.reding@gmail.com>
> > Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
> 
> Greg, any objections against this one?

Greg, if this isn't problematic, I'd still like to take it for v4.4.

Any chance you can have a look at it?

> > ---
> > 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_defer_all_probes_disable() - Disable deferring of device's probes
> > + *
> > + *	It will restore normal behavior and trigger re-probing of deferred
> > + * devices.
> > + */
> > +void device_defer_all_probes_disable(void)
> > +{
> > +	defer_all_probes = false;
> > +	driver_deferred_probe_trigger();
> > +}
> > +
> > +/**
> >   * deferred_probe_initcall() - Enable probing of deferred devices
> >   *
> >   * We don't want to get in the way when the bulk of drivers are getting probed.
> > @@ -277,9 +308,20 @@ static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
> >  
> >  static int really_probe(struct device *dev, struct device_driver *drv)
> >  {
> > -	int ret = 0;
> > +	int ret = -EPROBE_DEFER;
> >  	int local_trigger_count = atomic_read(&deferred_trigger_count);
> >  
> > +	if (defer_all_probes) {
> > +		/*
> > +		 * Value of defer_all_probes can be set only by
> > +		 * device_defer_all_probes_enable() which, in turn, will call
> > +		 * wait_for_device_probe() right after that to avoid any races.
> > +		 */
> > +		dev_dbg(dev, "Driver %s force probe deferral\n", drv->name);
> > +		driver_deferred_probe_add(dev);
> > +		return ret;
> > +	}
> > +
> >  	atomic_inc(&probe_count);
> >  	pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
> >  		 drv->bus->name, __func__, drv->name, dev_name(dev));
> > @@ -391,6 +433,10 @@ int driver_probe_done(void)
> >   */
> >  void wait_for_device_probe(void)
> >  {
> > +	/* wait for the deferred probe workqueue to finish */
> > +	if (driver_deferred_probe_enable)
> > +		flush_workqueue(deferred_wq);
> > +
> >  	/* wait for the known devices to complete their probing */
> >  	wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
> >  	async_synchronize_full();
> > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> > index 1710c26..eeb2bb7 100644
> > --- a/drivers/base/power/main.c
> > +++ b/drivers/base/power/main.c
> > @@ -963,6 +963,9 @@ void dpm_complete(pm_message_t state)
> >  	}
> >  	list_splice(&list, &dpm_list);
> >  	mutex_unlock(&dpm_list_mtx);
> > +
> > +	/* Allow device probing and trigger re-probing of deferred devices */
> > +	device_defer_all_probes_disable();
> >  	trace_suspend_resume(TPS("dpm_complete"), state.event, false);
> >  }
> >  
> > @@ -1624,6 +1627,20 @@ int dpm_prepare(pm_message_t state)
> >  	trace_suspend_resume(TPS("dpm_prepare"), state.event, true);
> >  	might_sleep();
> >  
> > +	/*
> > +	 * Give a chance for the known devices to complete their probes, before
> > +	 * disable probing of devices. This sync point is important at least
> > +	 * at boot time + hibernation restore.
> > +	 */
> > +	wait_for_device_probe();
> > +	/*
> > +	 * It is unsafe if probing of devices will happen during suspend or
> > +	 * hibernation and system behavior will be unpredictable in this case.
> > +	 * So, let's prohibit device's probing here and defer their probes
> > +	 * instead. The normal behavior will be restored in dpm_complete().
> > +	 */
> > +	device_defer_all_probes_enable();
> > +
> >  	mutex_lock(&dpm_list_mtx);
> >  	while (!list_empty(&dpm_list)) {
> >  		struct device *dev = to_device(dpm_list.next);
> > 
> 

Thanks,
Rafael