PM: sleep: core: Restrict power.set_active propagation

Commit 3775fc5 ("PM: sleep: core: Synchronize runtime PM status of
parents and children") exposed an issue related to simple_pm_bus_pm_ops
that uses pm_runtime_force_suspend() and pm_runtime_force_resume() as
bus type PM callbacks for the noirq phases of system-wide suspend and
resume.

The problem is that pm_runtime_force_suspend() does not distinguish
runtime-suspended devices from devices for which runtime PM has never
been enabled, so if it sees a device with runtime PM status set to
RPM_ACTIVE, it will assume that runtime PM is enabled for that device
and so it will attempt to suspend it with the help of its runtime PM
callbacks which may not be ready for that.  As it turns out, this
causes simple_pm_bus_runtime_suspend() to crash due to a NULL pointer
dereference.

Another problem related to the above commit and simple_pm_bus_pm_ops is
that setting runtime PM status of a device handled by the latter to
RPM_ACTIVE will actually prevent it from being resumed because
pm_runtime_force_resume() only resumes devices with runtime PM status
set to RPM_SUSPENDED.

To mitigate these issues, do not allow power.set_active to propagate
beyond the parent of the device with DPM_FLAG_SMART_SUSPEND set that
will need to be resumed, which should be a sufficient stop-gap for the
time being, but they will need to be properly addressed in the future
because in general during system-wide resume it is necessary to resume
all devices in a dependency chain in which at least one device is going
to be resumed.

Fixes: 3775fc5 ("PM: sleep: core: Synchronize runtime PM status of parents and children")
Closes: https://lore.kernel.org/linux-pm/1c2433d4-7e0f-4395-b841-b8eac7c25651@nvidia.com/
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/6137505.lOV4Wx5bFT@rjwysocki.net

Author: rafaeljw

drivers/base/power/main.c

@@ -1191,24 +1191,18 @@ static pm_message_t resume_event(pm_message_t sleep_state)
 	return PMSG_ON;
 }
 
-static void dpm_superior_set_must_resume(struct device *dev, bool set_active)
+static void dpm_superior_set_must_resume(struct device *dev)
 {
 	struct device_link *link;
 	int idx;
 
-	if (dev->parent) {
+	if (dev->parent)
 		dev->parent->power.must_resume = true;
-		if (set_active)
-			dev->parent->power.set_active = true;
-	}
 
 	idx = device_links_read_lock();
 
-	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node) {
+	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node)
 		link->supplier->power.must_resume = true;
-		if (set_active)
-			link->supplier->power.set_active = true;
-	}
 
 	device_links_read_unlock(idx);
 }
@@ -1287,9 +1281,12 @@ static int device_suspend_noirq(struct device *dev, pm_message_t state, bool asy
 		dev->power.must_resume = true;
 
 	if (dev->power.must_resume) {
-		dev->power.set_active = dev->power.set_active ||
-			dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND);
-		dpm_superior_set_must_resume(dev, dev->power.set_active);
+		if (dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND)) {
+			dev->power.set_active = true;
+			if (dev->parent && !dev->parent->power.ignore_children)
+				dev->parent->power.set_active = true;
+		}
+		dpm_superior_set_must_resume(dev);
 	}
 
 Complete: