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Subject[PATCH v2 4/9] driver core: Fix handling of runtime PM flags in device_link_add()
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

After commit ead18c23c263 ("driver core: Introduce device links
reference counting"), if there is a link between the given supplier
and the given consumer already, device_link_add() will refcount it
and return it unconditionally without updating its flags. It is
possible, however, that the second (or any subsequent) caller of
device_link_add() for the same consumer-supplier pair will pass
DL_FLAG_PM_RUNTIME, possibly along with DL_FLAG_RPM_ACTIVE, in flags
to it and the existing link may not behave as expected then.

First, if DL_FLAG_PM_RUNTIME is not set in the existing link's flags
at all, it needs to be set like during the original initialization of
the link.

Second, if DL_FLAG_RPM_ACTIVE is passed to device_link_add() in flags
(in addition to DL_FLAG_PM_RUNTIME), the existing link should to be
updated to reflect the "active" runtime PM configuration of the
consumer-supplier pair and extra care must be taken here to avoid
possible destructive races with runtime PM of the consumer.

To that end, redefine the rpm_active field in struct device_link
as a refcount, initialize it to 1 and make rpm_resume() (for the
consumer) and device_link_add() increment it whenever they acquire
a runtime PM reference on the supplier device. Accordingly, make
rpm_suspend() (for the consumer) and pm_runtime_clean_up_links()
decrement it and drop runtime PM references to the supplier
device in a loop until rpm_active becones 1 again.

Fixes: ead18c23c263 ("driver core: Introduce device links reference counting")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/base/core.c | 45 ++++++++++++++++++++++++++++---------------
drivers/base/power/runtime.c | 26 ++++++++++--------------
include/linux/device.h | 2 -
3 files changed, 42 insertions(+), 31 deletions(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -165,6 +165,19 @@ void device_pm_move_to_tail(struct devic
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.
@@ -201,7 +214,6 @@ struct device_link *device_link_add(stru
struct device *supplier, u32 flags)
{
struct device_link *link;
- bool rpm_put_supplier = false;

if (!consumer || !supplier ||
(flags & DL_FLAG_STATELESS &&
@@ -213,7 +225,6 @@ struct device_link *device_link_add(stru
pm_runtime_put_noidle(supplier);
return NULL;
}
- rpm_put_supplier = true;
}

device_links_write_lock();
@@ -249,6 +260,15 @@ struct device_link *device_link_add(stru
if (flags & DL_FLAG_AUTOREMOVE_SUPPLIER)
link->flags |= DL_FLAG_AUTOREMOVE_SUPPLIER;

+ if (flags & DL_FLAG_PM_RUNTIME) {
+ if (!(link->flags & DL_FLAG_PM_RUNTIME)) {
+ device_link_rpm_prepare(consumer, supplier);
+ link->flags |= DL_FLAG_PM_RUNTIME;
+ }
+ if (flags & DL_FLAG_RPM_ACTIVE)
+ refcount_inc(&link->rpm_active);
+ }
+
kref_get(&link->kref);
goto out;
}
@@ -257,20 +277,15 @@ struct device_link *device_link_add(stru
if (!link)
goto out;

+ refcount_set(&link->rpm_active, 1);
+
if (flags & DL_FLAG_PM_RUNTIME) {
- if (flags & DL_FLAG_RPM_ACTIVE) {
- link->rpm_active = true;
- rpm_put_supplier = false;
- }
- 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);
+ if (flags & DL_FLAG_RPM_ACTIVE)
+ refcount_inc(&link->rpm_active);
+
+ device_link_rpm_prepare(consumer, supplier);
}
+
get_device(supplier);
link->supplier = supplier;
INIT_LIST_HEAD(&link->s_node);
@@ -333,7 +348,7 @@ struct device_link *device_link_add(stru
device_pm_unlock();
device_links_write_unlock();

- if (rpm_put_supplier)
+ if ((flags & DL_FLAG_PM_RUNTIME && flags & DL_FLAG_RPM_ACTIVE) && !link)
pm_runtime_put(supplier);

return link;
Index: linux-pm/include/linux/device.h
===================================================================
--- linux-pm.orig/include/linux/device.h
+++ linux-pm/include/linux/device.h
@@ -853,7 +853,7 @@ struct device_link {
struct list_head c_node;
enum device_link_state status;
u32 flags;
- bool rpm_active;
+ refcount_t rpm_active;
struct kref kref;
#ifdef CONFIG_SRCU
struct rcu_head rcu_head;
Index: linux-pm/drivers/base/power/runtime.c
===================================================================
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -259,11 +259,8 @@ static int rpm_get_suppliers(struct devi
list_for_each_entry_rcu(link, &dev->links.suppliers, c_node) {
int retval;

- if (!(link->flags & DL_FLAG_PM_RUNTIME))
- continue;
-
- if (READ_ONCE(link->status) == DL_STATE_SUPPLIER_UNBIND ||
- link->rpm_active)
+ if (!(link->flags & DL_FLAG_PM_RUNTIME) ||
+ READ_ONCE(link->status) == DL_STATE_SUPPLIER_UNBIND)
continue;

retval = pm_runtime_get_sync(link->supplier);
@@ -272,7 +269,7 @@ static int rpm_get_suppliers(struct devi
pm_runtime_put_noidle(link->supplier);
return retval;
}
- link->rpm_active = true;
+ refcount_inc(&link->rpm_active);
}
return 0;
}
@@ -281,12 +278,13 @@ static void rpm_put_suppliers(struct dev
{
struct device_link *link;

- list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
- if (link->rpm_active &&
- READ_ONCE(link->status) != DL_STATE_SUPPLIER_UNBIND) {
+ list_for_each_entry_rcu(link, &dev->links.suppliers, c_node) {
+ if (READ_ONCE(link->status) == DL_STATE_SUPPLIER_UNBIND)
+ continue;
+
+ while (refcount_dec_not_one(&link->rpm_active))
pm_runtime_put(link->supplier);
- link->rpm_active = false;
- }
+ }
}

/**
@@ -1539,7 +1537,7 @@ void pm_runtime_remove(struct device *de
*
* Check links from this device to any consumers and if any of them have active
* runtime PM references to the device, drop the usage counter of the device
- * (once per link).
+ * (as many times as needed).
*
* Links with the DL_FLAG_STATELESS flag set are ignored.
*
@@ -1561,10 +1559,8 @@ void pm_runtime_clean_up_links(struct de
if (link->flags & DL_FLAG_STATELESS)
continue;

- if (link->rpm_active) {
+ while (refcount_dec_not_one(&link->rpm_active))
pm_runtime_put_noidle(dev);
- link->rpm_active = false;
- }
}

device_links_read_unlock(idx);
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