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PM: runtime: Add safety net to supplier device release

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[ Upstream commit d1579e6119 ]

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: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Rafael J. Wysocki 2021-12-10 17:10:13 +01:00 committed by Greg Kroah-Hartman
parent 4586d164c3
commit fddbdd20c8
3 changed files with 34 additions and 13 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
drivers/base/core.c
View file

@ -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);

41
drivers/base/power/runtime.c
View file

@ -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)
@ -1770,9 +1791,7 @@ 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)

3
include/linux/pm_runtime.h
View file

@ -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 */