PM / sleep: prohibit devices probing during suspend/hibernation

It is unsafe [1] 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 in dpm_prepare() and defer their
probing instead. The normal behavior will be restored in
dpm_complete().

This patch introduces new DD core APIs:
 device_block_probing()
   It will disable probing of devices and defer their probes instead.
 device_unblock_probing()
   It will restore normal behavior and trigger re-probing of deferred
   devices.

[1] https://lkml.org/lkml/2015/9/11/554

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/base/base.h b/drivers/base/base.h
index 1782f3a..e05db38 100644 (file)
--- 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_block_probing(void);
+extern void device_unblock_probing(void);
 
 /* /sys/devices directory */
 extern struct kset *devices_kset;

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index a641cf3..b605f73 100644 (file)
--- 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_block_probing() - Block/defere device's probes
+ *
+ *     It will disable probing of devices and defer their probes instead.
+ */
+void device_block_probing(void)
+{
+       defer_all_probes = true;
+       /* sync with probes to avoid races. */
+       wait_for_device_probe();
+}
+
+/**
+ * device_unblock_probing() - Unblock/enable device's probes
+ *
+ *     It will restore normal behavior and trigger re-probing of deferred
+ * devices.
+ */
+void device_unblock_probing(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));
@@ -393,6 +435,10 @@ 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..9d626ac 100644 (file)
--- 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_unblock_probing();
        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_block_probing();
+
        mutex_lock(&dpm_list_mtx);
        while (!list_empty(&dpm_list)) {
                struct device *dev = to_device(dpm_list.next);