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Subject[PATCH 4.19 221/639] driver core: Fix PM-runtime for links added during consumer probe
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

[ Upstream commit 36003d4cf57ca431fb3f94d317bcca426a2394d6 ]

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>
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index ab08211ba5d2d..742bc60e9ccac 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -253,7 +253,7 @@ struct device_link *device_link_add(struct device *consumer,
link->flags |= DL_FLAG_PM_RUNTIME;
}
if (flags & DL_FLAG_RPM_ACTIVE)
- pm_runtime_active_link(link, supplier);
+ refcount_inc(&link->rpm_active);
}

kref_get(&link->kref);
@@ -268,7 +268,7 @@ struct device_link *device_link_add(struct device *consumer,

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);
}
diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 0527890b4c191..303ce7d54a306 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -1571,6 +1571,7 @@ void pm_runtime_get_suppliers(struct device *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);
}
@@ -1590,9 +1591,11 @@ 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 &&
- 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);
}
@@ -1604,26 +1607,6 @@ 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);
diff --git a/include/linux/device.h b/include/linux/device.h
index b8fd2a1f859db..e9d1c768f972a 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -854,6 +854,7 @@ struct device_link {
#ifdef CONFIG_SRCU
struct rcu_head rcu_head;
#endif
+ bool supplier_preactivated; /* Owned by consumer probe. */
};

/**
diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
index bace7df51af4d..f0fc4700b6ff5 100644
--- a/include/linux/pm_runtime.h
+++ b/include/linux/pm_runtime.h
@@ -59,8 +59,6 @@ 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)
@@ -178,8 +176,6 @@ 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 */
--
2.20.1


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