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Subject[PATCH] driver core: Fix PM-runtime for links added during consumer probe
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Commit 4c06c4e6cf63 ("driver core: Fix possible supplier PM-usage
counter imbalance") introduced a regression that causes suppliers
to be suspended prematurely for device links added during consumer
driver probe if the initial PM-runtime status of the consumer is
"suspended" and the consumer is resumed after adding the link and
before pm_runtime_put_suppliers() is called. In that case,
pm_runtime_put_suppliers() will drop the rpm_active refcount for
the link by one and (since rpm_active is equal to two after the
preceding consumer resume) the supplier's PM-runtime usage counter
will be decremented, which may cause the supplier to suspend even
though the consumer's PM-runtime status is "active".

For this reason, partially revert commit 4c06c4e6cf63 as the problem
it tried to fix needs to be addressed somewhat differently, and
change pm_runtime_get_suppliers() and pm_runtime_put_suppliers() so
that the latter only drops rpm_active references acquired by the
former. [This requires adding a new field to struct device_link,
but I coulnd't find a cleaner way to address the issue that would
work in all cases.]

This causes pm_runtime_put_suppliers() to effectively ignore device
links added during consumer probe, so device_link_add() doesn't need
to worry about ensuring that suppliers will remain active after
pm_runtime_put_suppliers() for links created with DL_FLAG_RPM_ACTIVE
set and it only needs to bump up rpm_active by one for those links,
so pm_runtime_active_link() is not necessary any more.

Fixes: 4c06c4e6cf63 ("driver core: Fix possible supplier PM-usage counter imbalance")
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

Changes from the RFC version:
- T-by and R-by tags from Jon and Ulf.
- More details in the changelog.

---
drivers/base/core.c | 4 ++--
drivers/base/power/runtime.c | 29 ++++++-----------------------
include/linux/device.h | 1 +
include/linux/pm_runtime.h | 4 ----
4 files changed, 9 insertions(+), 29 deletions(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -277,7 +277,7 @@ struct device_link *device_link_add(stru
link->flags |= DL_FLAG_PM_RUNTIME;
}
if (flags & DL_FLAG_RPM_ACTIVE)
- pm_runtime_active_link(link, supplier);
+ refcount_inc(&link->rpm_active);
}

if (flags & DL_FLAG_STATELESS) {
@@ -310,7 +310,7 @@ struct device_link *device_link_add(stru

if (flags & DL_FLAG_PM_RUNTIME) {
if (flags & DL_FLAG_RPM_ACTIVE)
- pm_runtime_active_link(link, supplier);
+ refcount_inc(&link->rpm_active);

pm_runtime_new_link(consumer);
}
Index: linux-pm/drivers/base/power/runtime.c
===================================================================
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -1656,6 +1656,7 @@ void pm_runtime_get_suppliers(struct dev

list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
if (link->flags & DL_FLAG_PM_RUNTIME) {
+ link->supplier_preactivated = true;
refcount_inc(&link->rpm_active);
pm_runtime_get_sync(link->supplier);
}
@@ -1675,9 +1676,11 @@ 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 &&
- refcount_dec_not_one(&link->rpm_active))
- pm_runtime_put(link->supplier);
+ if (link->supplier_preactivated) {
+ link->supplier_preactivated = false;
+ if (refcount_dec_not_one(&link->rpm_active))
+ pm_runtime_put(link->supplier);
+ }

device_links_read_unlock(idx);
}
@@ -1689,26 +1692,6 @@ 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/include/linux/device.h
===================================================================
--- linux-pm.orig/include/linux/device.h
+++ linux-pm/include/linux/device.h
@@ -861,6 +861,7 @@ struct device_link {
#ifdef CONFIG_SRCU
struct rcu_head rcu_head;
#endif
+ bool supplier_preactivated; /* Owned by consumer probe. */
};

/**
Index: linux-pm/include/linux/pm_runtime.h
===================================================================
--- linux-pm.orig/include/linux/pm_runtime.h
+++ linux-pm/include/linux/pm_runtime.h
@@ -59,8 +59,6 @@ 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)
@@ -180,8 +178,6 @@ 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 */
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