driver core: Fix PM-runtime for links added during consumer probe

Commit 4c06c4e6cf ("driver core: Fix possible supplier PM-usage
counter imbalance") introduced a regression that causes suppliers
to be suspended prematurely for device links added during consumer
driver probe if the initial PM-runtime status of the consumer is
"suspended" and the consumer is resumed after adding the link and
before pm_runtime_put_suppliers() is called.  In that case,
pm_runtime_put_suppliers() will drop the rpm_active refcount for
the link by one and (since rpm_active is equal to two after the
preceding consumer resume) the supplier's PM-runtime usage counter
will be decremented, which may cause the supplier to suspend even
though the consumer's PM-runtime status is "active".

For this reason, partially revert commit 4c06c4e6cf as the problem
it tried to fix needs to be addressed somewhat differently, and
change pm_runtime_get_suppliers() and pm_runtime_put_suppliers() so
that the latter only drops rpm_active references acquired by the
former.  [This requires adding a new field to struct device_link,
but I coulnd't find a cleaner way to address the issue that would
work in all cases.]

This causes pm_runtime_put_suppliers() to effectively ignore device
links added during consumer probe, so device_link_add() doesn't need
to worry about ensuring that suppliers will remain active after
pm_runtime_put_suppliers() for links created with DL_FLAG_RPM_ACTIVE
set and it only needs to bump up rpm_active by one for those links,
so pm_runtime_active_link() is not necessary any more.

Fixes: 4c06c4e6cf ("driver core: Fix possible supplier PM-usage counter imbalance")
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/core.c

@@ -277,7 +277,7 @@ struct device_link *device_link_add(struct device *consumer,
 				link->flags |= DL_FLAG_PM_RUNTIME;
 			}
 			if (flags & DL_FLAG_RPM_ACTIVE)
-				pm_runtime_active_link(link, supplier);
+				refcount_inc(&link->rpm_active);
 		}
 
 		if (flags & DL_FLAG_STATELESS) {
@@ -310,7 +310,7 @@ struct device_link *device_link_add(struct device *consumer,
 
 	if (flags & DL_FLAG_PM_RUNTIME) {
 		if (flags & DL_FLAG_RPM_ACTIVE)
-			pm_runtime_active_link(link, supplier);
+			refcount_inc(&link->rpm_active);
 
 		pm_runtime_new_link(consumer);
 	}

drivers/base/power/runtime.c

@@ -1626,6 +1626,7 @@ void pm_runtime_get_suppliers(struct device *dev)
 
 	list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
 		if (link->flags & DL_FLAG_PM_RUNTIME) {
+			link->supplier_preactivated = true;
 			refcount_inc(&link->rpm_active);
 			pm_runtime_get_sync(link->supplier);
 		}
@@ -1645,9 +1646,11 @@ void pm_runtime_put_suppliers(struct device *dev)
 	idx = device_links_read_lock();
 
 	list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
-		if (link->flags & DL_FLAG_PM_RUNTIME &&
-		    refcount_dec_not_one(&link->rpm_active))
-			pm_runtime_put(link->supplier);
+		if (link->supplier_preactivated) {
+			link->supplier_preactivated = false;
+			if (refcount_dec_not_one(&link->rpm_active))
+				pm_runtime_put(link->supplier);
+		}
 
 	device_links_read_unlock(idx);
 }
@@ -1659,26 +1662,6 @@ void pm_runtime_new_link(struct device *dev)
 	spin_unlock_irq(&dev->power.lock);
 }
 
-/**
- * pm_runtime_active_link - Set up new device link as active for PM-runtime.
- * @link: Device link to be set up as active.
- * @supplier: Supplier end of the link.
- *
- * Add 2 to the rpm_active refcount of @link and increment the PM-runtime
- * usage counter of @supplier once more in case the link is being added while
- * the consumer driver is probing and pm_runtime_put_suppliers() will be called
- * subsequently.
- *
- * Note that this doesn't prevent rpm_put_suppliers() from decreasing the link's
- * rpm_active refcount down to one, so runtime suspend of the consumer end of
- * @link is not affected.
- */
-void pm_runtime_active_link(struct device_link *link, struct device *supplier)
-{
-	refcount_add(2, &link->rpm_active);
-	pm_runtime_get_noresume(supplier);
-}
-
 void pm_runtime_drop_link(struct device *dev)
 {
 	spin_lock_irq(&dev->power.lock);

include/linux/device.h

@@ -861,6 +861,7 @@ struct device_link {
 #ifdef CONFIG_SRCU
 	struct rcu_head rcu_head;
 #endif
+	bool supplier_preactivated; /* Owned by consumer probe. */
 };
 
 /**

include/linux/pm_runtime.h

@@ -59,8 +59,6 @@ extern void pm_runtime_clean_up_links(struct device *dev);
 extern void pm_runtime_get_suppliers(struct device *dev);
 extern void pm_runtime_put_suppliers(struct device *dev);
 extern void pm_runtime_new_link(struct device *dev);
-extern void pm_runtime_active_link(struct device_link *link,
-				   struct device *supplier);
 extern void pm_runtime_drop_link(struct device *dev);
 
 static inline void pm_suspend_ignore_children(struct device *dev, bool enable)
@@ -178,8 +176,6 @@ static inline void pm_runtime_clean_up_links(struct device *dev) {}
 static inline void pm_runtime_get_suppliers(struct device *dev) {}
 static inline void pm_runtime_put_suppliers(struct device *dev) {}
 static inline void pm_runtime_new_link(struct device *dev) {}
-static inline void pm_runtime_active_link(struct device_link *link,
-					  struct device *supplier) {}
 static inline void pm_runtime_drop_link(struct device *dev) {}
 
 #endif /* !CONFIG_PM */