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Message-ID: <5148641.xH2horsriG@vostro.rjw.lan>
Date: Mon, 02 Nov 2015 02:25 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Grygorii Strashko <grygorii.strashko@...com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: 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 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?
> ---
> 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
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