PM: Block enabling of runtime PM during system suspend

If device_prepare() runs on a device that has never had runtime
PM enabled so far, it may reasonably assume that runtime PM will
not be enabled for that device during the system suspend-resume
cycle currently in progress, but this has never been guaranteed.

To verify this assumption, make device_prepare() arrange for
triggering a device warning accompanied by a call trace dump if
runtime PM is enabled for such a device after it has returned.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://patch.msgid.link/6131109.lOV4Wx5bFT@rjwysocki.net

drivers/base/power/main.c

@@ -1109,6 +1109,8 @@ static void device_complete(struct device *dev, pm_message_t state)
 	device_unlock(dev);
 
 out:
+	/* If enabling runtime PM for the device is blocked, unblock it. */
+	pm_runtime_unblock(dev);
 	pm_runtime_put(dev);
 }
 
@@ -1815,6 +1817,13 @@ static int device_prepare(struct device *dev, pm_message_t state)
 	 * it again during the complete phase.
 	 */
 	pm_runtime_get_noresume(dev);
+	/*
+	 * If runtime PM is disabled for the device at this point and it has
+	 * never been enabled so far, it should not be enabled until this system
+	 * suspend-resume cycle is complete, so prepare to trigger a warning on
+	 * subsequent attempts to enable it.
+	 */
+	pm_runtime_block_if_disabled(dev);
 
 	if (dev->power.syscore)
 		return 0;

drivers/base/power/runtime.c

@@ -1460,6 +1460,26 @@ int pm_runtime_barrier(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(pm_runtime_barrier);
 
+void pm_runtime_block_if_disabled(struct device *dev)
+{
+	spin_lock_irq(&dev->power.lock);
+
+	if (dev->power.disable_depth && dev->power.last_status == RPM_INVALID)
+		dev->power.last_status = RPM_BLOCKED;
+
+	spin_unlock_irq(&dev->power.lock);
+}
+
+void pm_runtime_unblock(struct device *dev)
+{
+	spin_lock_irq(&dev->power.lock);
+
+	if (dev->power.last_status == RPM_BLOCKED)
+		dev->power.last_status = RPM_INVALID;
+
+	spin_unlock_irq(&dev->power.lock);
+}
+
 void __pm_runtime_disable(struct device *dev, bool check_resume)
 {
 	spin_lock_irq(&dev->power.lock);
@@ -1518,6 +1538,10 @@ void pm_runtime_enable(struct device *dev)
 	if (--dev->power.disable_depth > 0)
 		goto out;
 
+	if (dev->power.last_status == RPM_BLOCKED) {
+		dev_warn(dev, "Attempt to enable runtime PM when it is blocked\n");
+		dump_stack();
+	}
 	dev->power.last_status = RPM_INVALID;
 	dev->power.accounting_timestamp = ktime_get_mono_fast_ns();
 

include/linux/pm.h

@@ -597,6 +597,7 @@ enum rpm_status {
 	RPM_RESUMING,
 	RPM_SUSPENDED,
 	RPM_SUSPENDING,
+	RPM_BLOCKED,
 };
 
 /*

include/linux/pm_runtime.h

@@ -77,6 +77,8 @@ extern int pm_runtime_get_if_in_use(struct device *dev);
 extern int pm_schedule_suspend(struct device *dev, unsigned int delay);
 extern int __pm_runtime_set_status(struct device *dev, unsigned int status);
 extern int pm_runtime_barrier(struct device *dev);
+extern void pm_runtime_block_if_disabled(struct device *dev);
+extern void pm_runtime_unblock(struct device *dev);
 extern void pm_runtime_enable(struct device *dev);
 extern void __pm_runtime_disable(struct device *dev, bool check_resume);
 extern void pm_runtime_allow(struct device *dev);
@@ -271,6 +273,8 @@ static inline int pm_runtime_get_if_active(struct device *dev)
 static inline int __pm_runtime_set_status(struct device *dev,
 					    unsigned int status) { return 0; }
 static inline int pm_runtime_barrier(struct device *dev) { return 0; }
+static inline void pm_runtime_block_if_disabled(struct device *dev) {}
+static inline void pm_runtime_unblock(struct device *dev) {}
 static inline void pm_runtime_enable(struct device *dev) {}
 static inline void __pm_runtime_disable(struct device *dev, bool c) {}
 static inline void pm_runtime_allow(struct device *dev) {}