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

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Message-ID: <20151105221903.GA4919@amd>
Date:	Thu, 5 Nov 2015 23:19:03 +0100
From:	Pavel Machek <pavel@....cz>
To:	Grygorii Strashko <grygorii.strashko@...com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>, 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 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()?

Thanks,
									Pavel

-- 
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