PM: runtime: Fix supplier device management during consumer probe

From: Rafael J. Wysocki <[email protected]>

Because pm_runtime_get_suppliers() bumps up the rpm_active counter of each device link to a supplier of the given device in addition to bumping up the supplier's PM-runtime usage counter, a runtime suspend of the consumer device may case the latter to go down to 0 when pm_runtime_put_suppliers() is running on a remote CPU. If that happens after pm_runtime_put_suppliers() has released power.lock for the consumer device, and a runtime resume of that device takes place immediately after it, before pm_runtime_put() is called for the supplier, that pm_runtime_put() call may cause the supplier to be suspended even though the consumer is active.

To prevent that from happening, modify pm_runtime_get_suppliers() to call pm_runtime_get_sync() for the given device's suppliers without touching the rpm_active counters of the involved device links Accordingly, modify pm_runtime_put_suppliers() to call pm_runtime_put() for the given device's suppliers without looking at the rpm_active counters of the device links at hand. [This is analogous to what happened before commit 4c06c4e6cf63 ("driver core: Fix possible supplier PM-usage counter imbalance").]

Since pm_runtime_get_suppliers() sets supplier_preactivated for each device link where the supplier's PM-runtime usage counter has been incremented and pm_runtime_put_suppliers() calls pm_runtime_put() for the suppliers whose device links have supplier_preactivated set, the PM-runtime usage counter is balanced for each supplier and this is independent of the runtime suspend and resume of the consumer device.

However, in case a device link with DL_FLAG_PM_RUNTIME set is dropped during the consumer device probe, so pm_runtime_get_suppliers() bumps up the supplier's PM-runtime usage counter, but it cannot be dropped by pm_runtime_put_suppliers(), make device_link_release_fn() take care of that.

Fixes 4c06c4e6cf63 ("driver core: Fix possible supplier PM-usage counter imbalance")

Reported-by Peter Wang <[email protected]>

Signed-off-by Rafael J. Wysocki <[email protected]>

---
 drivers/base/core.c          |   10 ++++++++++
 drivers/base/power/runtime.c |   14 +-------------
 2 files changed, 11 insertions(+), 13 deletions(-)

From: Rafael J. Wysocki <[email protected]>

Because pm_runtime_get_suppliers() bumps up the rpm_active counter of each device link to a supplier of the given device in addition to bumping up the supplier's PM-runtime usage counter, a runtime suspend of the consumer device may case the latter to go down to 0 when pm_runtime_put_suppliers() is running on a remote CPU. If that happens after pm_runtime_put_suppliers() has released power.lock for the consumer device, and a runtime resume of that device takes place immediately after it, before pm_runtime_put() is called for the supplier, that pm_runtime_put() call may cause the supplier to be suspended even though the consumer is active.

To prevent that from happening, modify pm_runtime_get_suppliers() to call pm_runtime_get_sync() for the given device's suppliers without touching the rpm_active counters of the involved device links Accordingly, modify pm_runtime_put_suppliers() to call pm_runtime_put() for the given device's suppliers without looking at the rpm_active counters of the device links at hand. [This is analogous to what happened before commit 4c06c4e6cf63 ("driver core: Fix possible supplier PM-usage counter imbalance").]

Since pm_runtime_get_suppliers() sets supplier_preactivated for each device link where the supplier's PM-runtime usage counter has been incremented and pm_runtime_put_suppliers() calls pm_runtime_put() for the suppliers whose device links have supplier_preactivated set, the PM-runtime usage counter is balanced for each supplier and this is independent of the runtime suspend and resume of the consumer device.

However, in case a device link with DL_FLAG_PM_RUNTIME set is dropped during the consumer device probe, so pm_runtime_get_suppliers() bumps up the supplier's PM-runtime usage counter, but it cannot be dropped by pm_runtime_put_suppliers(), make device_link_release_fn() take care of that.

Fixes 4c06c4e6cf63 ("driver core: Fix possible supplier PM-usage counter imbalance")

Reported-by Peter Wang <[email protected]>

Signed-off-by Rafael J. Wysocki <[email protected]>

---
  drivers/base/core.c          |   10 ++++++++++
  drivers/base/power/runtime.c |   14 +-------------
  2 files changed, 11 insertions(+), 13 deletions(-)

Index: linux-pm/drivers/base/power/runtime.c
===================================================================

drivers/base/power/runtime.c +1 -13

@@ -1768,7 +1768,6 @@ void pm_runtime_get_suppliers(struct dev
  		if (link->flags & DL_FLAG_PM_RUNTIME) {
  			link->supplier_preactivated = true;
  			pm_runtime_get_sync(link->supplier);
-			refcount_inc(&link->rpm_active);
  		}
 
  	device_links_read_unlock(idx);

@@ -1788,19 +1787,8 @@ void pm_runtime_put_suppliers(struct dev
  	list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,
  				device_links_read_lock_held())
  		if (link->supplier_preactivated) {
-			bool put;
-
  			link->supplier_preactivated = false;
-
-			spin_lock_irq(&dev->power.lock);
-
-			put = pm_runtime_status_suspended(dev) &&
-			      refcount_dec_not_one(&link->rpm_active);
-
-			spin_unlock_irq(&dev->power.lock);
-
-			if (put)
-				pm_runtime_put(link->supplier);
+			pm_runtime_put(link->supplier);
  		}
 
  	device_links_read_unlock(idx);

Index: linux-pm/drivers/base/core.c
===================================================================

drivers/base/core.c +3 -0

@@ -487,6 +487,16 @@ static void device_link_release_fn(struc
  	device_link_synchronize_removal();
 
  	pm_runtime_release_supplier(link);
+	/*
+	 * If supplier_preactivated is set, the link has been dropped between
+	 * the pm_runtime_get_suppliers() and pm_runtime_put_suppliers() calls