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

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

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?

> ---
> 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