Commit d1579e61 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

PM: runtime: Add safety net to supplier device release 



Because refcount_dec_not_one() returns true if the target refcount
becomes saturated, it is generally unsafe to use its return value as
a loop termination condition, but that is what happens when a device
link's supplier device is released during runtime PM suspend
operations and on device link removal.

To address this, introduce pm_runtime_release_supplier() to be used
in the above cases which will check the supplier device's runtime
PM usage counter in addition to the refcount_dec_not_one() return
value, so the loop can be terminated in case the rpm_active refcount
value becomes invalid, and update the code in question to use it as
appropriate.

This change is not expected to have any visible functional impact.

Reported-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
parent c24efa67

drivers/base/core.c

+1 −2
Original line number Diff line number Diff line
@@ -485,8 +485,7 @@ static void device_link_release_fn(struct work_struct *work) 
	/* Ensure that all references to the link object have been dropped. */

	device_link_synchronize_removal();



	while (refcount_dec_not_one(&link->rpm_active))

		pm_runtime_put(link->supplier);

	pm_runtime_release_supplier(link, true);



	put_device(link->consumer);

	put_device(link->supplier);

drivers/base/power/runtime.c

+30 −11
Original line number Diff line number Diff line
@@ -305,19 +305,40 @@ static int rpm_get_suppliers(struct device *dev) 
	return 0;

}



/**

 * pm_runtime_release_supplier - Drop references to device link's supplier.

 * @link: Target device link.

 * @check_idle: Whether or not to check if the supplier device is idle.

 *

 * Drop all runtime PM references associated with @link to its supplier device

 * and if @check_idle is set, check if that device is idle (and so it can be

 * suspended).

 */

void pm_runtime_release_supplier(struct device_link *link, bool check_idle)

{

	struct device *supplier = link->supplier;



	/*

	 * The additional power.usage_count check is a safety net in case

	 * the rpm_active refcount becomes saturated, in which case

	 * refcount_dec_not_one() would return true forever, but it is not

	 * strictly necessary.

	 */

	while (refcount_dec_not_one(&link->rpm_active) &&

	       atomic_read(&supplier->power.usage_count) > 0)

		pm_runtime_put_noidle(supplier);



	if (check_idle)

		pm_request_idle(supplier);

}



static void __rpm_put_suppliers(struct device *dev, bool try_to_suspend)

{

	struct device_link *link;



	list_for_each_entry_rcu(link, &dev->links.suppliers, c_node,

				device_links_read_lock_held()) {



		while (refcount_dec_not_one(&link->rpm_active))

			pm_runtime_put_noidle(link->supplier);



		if (try_to_suspend)

			pm_request_idle(link->supplier);

	}

				device_links_read_lock_held())

		pm_runtime_release_supplier(link, try_to_suspend);

}



static void rpm_put_suppliers(struct device *dev)
@@ -1777,9 +1798,7 @@ void pm_runtime_drop_link(struct device_link *link) 
		return;



	pm_runtime_drop_link_count(link->consumer);



	while (refcount_dec_not_one(&link->rpm_active))

		pm_runtime_put(link->supplier);

	pm_runtime_release_supplier(link, true);

}



static bool pm_runtime_need_not_resume(struct device *dev)

include/linux/pm_runtime.h

+3 −0
Original line number Diff line number Diff line
@@ -58,6 +58,7 @@ 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_drop_link(struct device_link *link);

extern void pm_runtime_release_supplier(struct device_link *link, bool check_idle);



extern int devm_pm_runtime_enable(struct device *dev);
@@ -283,6 +284,8 @@ 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_drop_link(struct device_link *link) {}

static inline void pm_runtime_release_supplier(struct device_link *link,

					       bool check_idle) {}



#endif /* !CONFIG_PM */