driver core: Fix possible supplier PM-usage counter imbalance

If a stateless device link to a certain supplier with
DL_FLAG_PM_RUNTIME set in the flags is added and then removed by the
consumer driver's probe callback, the supplier's PM-runtime usage
counter will be nonzero after that which effectively causes the
supplier to remain "always on" going forward.

Namely, device_link_add() called to add the link invokes
device_link_rpm_prepare() which notices that the consumer driver is
probing, so it increments the supplier's PM-runtime usage counter
with the assumption that the link will stay around until
pm_runtime_put_suppliers() is called by driver_probe_device(),
but if the link goes away before that point, the supplier's
PM-runtime usage counter will remain nonzero.

To prevent that from happening, first rework pm_runtime_get_suppliers()
and pm_runtime_put_suppliers() to use the rpm_active refounts of device
links and make the latter only drop rpm_active and the supplier's
PM-runtime usage counter for each link by one, unless rpm_active is
one already for it.  Next, modify device_link_add() to bump up the
new link's rpm_active refcount and the suppliers PM-runtime usage
counter by two, to prevent pm_runtime_put_suppliers(), if it is
called subsequently, from suspending the supplier prematurely (in
case its PM-runtime usage counter goes down to 0 in there).

Due to the way rpm_put_suppliers() works, this change does not
affect runtime suspend of the consumer ends of new device links (or,
generally, device links for which DL_FLAG_PM_RUNTIME has just been
set).

Fixes: e2f3cd831a28 ("driver core: Fix handling of runtime PM flags in device_link_add()")
Reported-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 17 deletions

diff --git a/drivers/base/core.c b/drivers/base/core.c
index abfce4f613f8..787190238753 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -165,19 +165,6 @@ void device_pm_move_to_tail(struct device *dev)
 	device_links_read_unlock(idx);
 }
 
-static void device_link_rpm_prepare(struct device *consumer,
-				    struct device *supplier)
-{
-	pm_runtime_new_link(consumer);
-	/*
-	 * If the link is being added by the consumer driver at probe time,
-	 * balance the decrementation of the supplier's runtime PM usage counter
-	 * after consumer probe in driver_probe_device().
-	 */
-	if (consumer->links.status == DL_DEV_PROBING)
-		pm_runtime_get_noresume(supplier);
-}
-
 /**
  * device_link_add - Create a link between two devices.
  * @consumer: Consumer end of the link.
@@ -286,11 +273,11 @@ struct device_link *device_link_add(struct device *consumer,
 
 		if (flags & DL_FLAG_PM_RUNTIME) {
 			if (!(link->flags & DL_FLAG_PM_RUNTIME)) {
-				device_link_rpm_prepare(consumer, supplier);
+				pm_runtime_new_link(consumer);
 				link->flags |= DL_FLAG_PM_RUNTIME;
 			}
 			if (flags & DL_FLAG_RPM_ACTIVE)
-				refcount_inc(&link->rpm_active);
+				pm_runtime_active_link(link, supplier);
 		}
 
 		if (flags & DL_FLAG_STATELESS) {
@@ -323,9 +310,9 @@ struct device_link *device_link_add(struct device *consumer,
 
 	if (flags & DL_FLAG_PM_RUNTIME) {
 		if (flags & DL_FLAG_RPM_ACTIVE)
-			refcount_inc(&link->rpm_active);
+			pm_runtime_active_link(link, supplier);
 
-		device_link_rpm_prepare(consumer, supplier);
+		pm_runtime_new_link(consumer);
 	}
 
 	get_device(supplier);