lkml.org 
[lkml]   [2019]   [Feb]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 2/2] driver core: Fix possible supplier PM-usage counter imbalance
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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>
---

Note that the issue had been there before commit e2f3cd831a28, but it was
overlooked by that commit and this change is a fix on top of it, so make
the Fixes: tag point to commit e2f3cd831a28 (instead of an earlier one
that the patch will not be applicable to).

---
drivers/base/core.c | 21 ++++-----------------
drivers/base/power/runtime.c | 27 +++++++++++++++++++++++++--
include/linux/pm_runtime.h | 4 ++++
3 files changed, 33 insertions(+), 19 deletions(-)

Index: linux-pm/drivers/base/power/runtime.c
===================================================================
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -1655,8 +1655,10 @@ void pm_runtime_get_suppliers(struct dev
idx = device_links_read_lock();

list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
- if (link->flags & DL_FLAG_PM_RUNTIME)
+ if (link->flags & DL_FLAG_PM_RUNTIME) {
+ refcount_inc(&link->rpm_active);
pm_runtime_get_sync(link->supplier);
+ }

device_links_read_unlock(idx);
}
@@ -1673,7 +1675,8 @@ void pm_runtime_put_suppliers(struct dev
idx = device_links_read_lock();

list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
- if (link->flags & DL_FLAG_PM_RUNTIME)
+ if (link->flags & DL_FLAG_PM_RUNTIME &&
+ refcount_dec_not_one(&link->rpm_active))
pm_runtime_put(link->supplier);

device_links_read_unlock(idx);
@@ -1686,6 +1689,26 @@ void pm_runtime_new_link(struct device *
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);
Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -165,19 +165,6 @@ 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.
@@ -286,11 +273,11 @@ struct device_link *device_link_add(stru

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(stru

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);
Index: linux-pm/include/linux/pm_runtime.h
===================================================================
--- linux-pm.orig/include/linux/pm_runtime.h
+++ linux-pm/include/linux/pm_runtime.h
@@ -59,6 +59,8 @@ extern void pm_runtime_clean_up_links(st
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)
@@ -178,6 +180,8 @@ static inline void pm_runtime_clean_up_l
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 */
\
 
 \ /
  Last update: 2019-02-12 13:11    [W:0.129 / U:0.184 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site