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driver core: Fix possible supplier PM-usage counter imbalance

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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: e2f3cd831a ("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>
This commit is contained in:
Rafael J. Wysocki 2019-02-12 13:08:10 +01:00 committed by Greg Kroah-Hartman
parent c1567f813a
commit 4c06c4e6cf
3 changed files with 33 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
drivers/base/core.c
View File

@ -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);

27
drivers/base/power/runtime.c
View File

@ -1625,8 +1625,10 @@ void pm_runtime_get_suppliers(struct device *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);
}
@ -1643,7 +1645,8 @@ void pm_runtime_put_suppliers(struct device *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);
@ -1656,6 +1659,26 @@ void pm_runtime_new_link(struct device *dev)
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);

4
include/linux/pm_runtime.h
View File

@ -59,6 +59,8 @@ extern void pm_runtime_clean_up_links(struct device *dev);
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)
@ -176,6 +178,8 @@ static inline void pm_runtime_clean_up_links(struct device *dev) {}
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 */