PM: Handle device registrations during suspend/resume

Modify the PM core to protect its data structures, specifically the
dpm_active list, from being corrupted if a child of the currently
suspending device is registered concurrently with its ->suspend()
callback.  In that case, since the new device (the child) is added
to dpm_active after its parent, the PM core will attempt to
suspend it after the parent, which is wrong.

Introduce a new member of struct dev_pm_info, called 'sleeping',
and use it to check if the parent of the device being added to
dpm_active has been suspended, in which case the device registration
fails.  Also, use 'sleeping' for checking if the ordering of devices
on dpm_active is correct.

Introduce variable 'all_sleeping' that will be set to 'true' once all
devices have been suspended and make new device registrations fail
until 'all_sleeping' is reset to 'false', in order to avoid having
unsuspended devices around while the system is going into a sleep state.

Remove pm_sleep_rwsem which is not necessary any more.

Special thanks to Alan Stern for discussions and suggestions that
lead to the creation of this patch.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 29 insertions, 51 deletions

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 26de2c0fda80..0e3991a437c6 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -54,7 +54,8 @@ static LIST_HEAD(dpm_destroy);
 
 static DEFINE_MUTEX(dpm_list_mtx);
 
-static DECLARE_RWSEM(pm_sleep_rwsem);
+/* 'true' if all devices have been suspended, protected by dpm_list_mtx */
+static bool all_sleeping;
 
 int (*platform_enable_wakeup)(struct device *dev, int is_on);
 
@@ -62,14 +63,28 @@ int (*platform_enable_wakeup)(struct device *dev, int is_on);
  *      device_pm_add - add a device to the list of active devices
  *      @dev:   Device to be added to the list
  */
-void device_pm_add(struct device *dev)
+int device_pm_add(struct device *dev)
 {
+        int error = 0;
+
         pr_debug("PM: Adding info for %s:%s\n",
                  dev->bus ? dev->bus->name : "No Bus",
                  kobject_name(&dev->kobj));
         mutex_lock(&dpm_list_mtx);
-        list_add_tail(&dev->power.entry, &dpm_active);
+        if ((dev->parent && dev->parent->power.sleeping) || all_sleeping) {
+                if (dev->parent->power.sleeping)
+                        dev_warn(dev,
+                                "parent %s is sleeping, will not add\n",
+                                dev->parent->bus_id);
+                else
+                        dev_warn(dev, "devices are sleeping, will not add\n");
+                WARN_ON(true);
+                error = -EBUSY;
+        } else {
+                list_add_tail(&dev->power.entry, &dpm_active);
+        }
         mutex_unlock(&dpm_list_mtx);
+        return error;
 }
 
 /**
@@ -107,32 +122,6 @@ void device_pm_schedule_removal(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(device_pm_schedule_removal);
 
-/**
- *      pm_sleep_lock - mutual exclusion for registration and suspend
- *
- *      Returns 0 if no suspend is underway and device registration
- *      may proceed, otherwise -EBUSY.
- */
-int pm_sleep_lock(void)
-{
-        if (down_read_trylock(&pm_sleep_rwsem))
-                return 0;
-
-        return -EBUSY;
-}
-
-/**
- *      pm_sleep_unlock - mutual exclusion for registration and suspend
- *
- *      This routine undoes the effect of device_pm_add_lock
- *      when a device's registration is complete.
- */
-void pm_sleep_unlock(void)
-{
-        up_read(&pm_sleep_rwsem);
-}
-
-
 /*------------------------- Resume routines -------------------------*/
 
 /**
@@ -242,11 +231,13 @@ static int resume_device(struct device *dev)
 static void dpm_resume(void)
 {
         mutex_lock(&dpm_list_mtx);
+        all_sleeping = false;
         while(!list_empty(&dpm_off)) {
                 struct list_head *entry = dpm_off.next;
                 struct device *dev = to_device(entry);
 
                 list_move_tail(entry, &dpm_active);
+                dev->power.sleeping = false;
                 mutex_unlock(&dpm_list_mtx);
                 resume_device(dev);
                 mutex_lock(&dpm_list_mtx);
@@ -285,7 +276,6 @@ void device_resume(void)
         might_sleep();
         dpm_resume();
         unregister_dropped_devices();
-        up_write(&pm_sleep_rwsem);
 }
 EXPORT_SYMBOL_GPL(device_resume);
 
@@ -421,6 +411,9 @@ static int dpm_suspend(pm_message_t state)
                 struct list_head *entry = dpm_active.prev;
                 struct device *dev = to_device(entry);
 
+                WARN_ON(dev->parent && dev->parent->power.sleeping);
+
+                dev->power.sleeping = true;
                 mutex_unlock(&dpm_list_mtx);
                 error = suspend_device(dev, state);
                 mutex_lock(&dpm_list_mtx);
@@ -432,11 +425,14 @@ static int dpm_suspend(pm_message_t state)
                                         (error == -EAGAIN ?
                                         " (please convert to suspend_late)" :
                                         ""));
+                        dev->power.sleeping = false;
                         break;
                 }
                 if (!list_empty(&dev->power.entry))
                         list_move(&dev->power.entry, &dpm_off);
         }
+        if (!error)
+                all_sleeping = true;
         mutex_unlock(&dpm_list_mtx);
 
         return error;
@@ -454,7 +450,6 @@ int device_suspend(pm_message_t state)
         int error;
 
         might_sleep();
-        down_write(&pm_sleep_rwsem);
         error = dpm_suspend(state);
         if (error)
                 device_resume();
diff --git a/drivers/base/power/power.h b/drivers/base/power/power.h
index e32d3bdb92c1..a6894f2a4b99 100644
--- a/drivers/base/power/power.h
+++ b/drivers/base/power/power.h
@@ -11,30 +11,13 @@ static inline struct device *to_device(struct list_head *entry)
         return container_of(entry, struct device, power.entry);
 }
 
-extern void device_pm_add(struct device *);
+extern int device_pm_add(struct device *);
 extern void device_pm_remove(struct device *);
-extern int pm_sleep_lock(void);
-extern void pm_sleep_unlock(void);
 
 #else /* CONFIG_PM_SLEEP */
 
-
-static inline void device_pm_add(struct device *dev)
-{
-}
-
-static inline void device_pm_remove(struct device *dev)
-{
-}
-
-static inline int pm_sleep_lock(void)
-{
-        return 0;
-}
-
-static inline void pm_sleep_unlock(void)
-{
-}
+static inline int device_pm_add(struct device *dev) { return 0; }
+static inline void device_pm_remove(struct device *dev) {}
 
 #endif