[PATCH] PM / runtime: Drop usage count for suppliers at device link removal

[PATCH] PM / runtime: Drop usage count for suppliers at device link removal

[Ulf Hansson]

In the case consumer device is runtime resumed, while the link to the
supplier is removed, the earlier call to pm_runtime_get_sync() made from
rpm_get_suppliers() does not get properly balanced with a corresponding
call to pm_runtime_put(). This leads to that suppliers remains to be
runtime resumed forever, while they don't need to.

Let's fix the behaviour by calling rpm_put_suppliers() when dropping a
device link. Not that, since rpm_put_suppliers() checks the
link->rpm_active flag, we can correctly avoid to call pm_runtime_put() in
cases when we shouldn't.

Reported-by: Todor Tomov <todor.tomov@linaro.org>
Fixes: 21d5c57b3726 ("PM / runtime: Use device links")
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---

Rafael, I am not sure if this is safe from locking point of view. The device
link write lock has been taken when pm_runtime_drop_link() is called, hence I
assume calling rpm_put_suppliers() should be fine!? If not, can you please
advise how to change?

Kind regards
Uffe

---
 drivers/base/power/runtime.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 8bef3cb..beb85c3 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -1607,6 +1607,8 @@ void pm_runtime_new_link(struct device *dev)
 
 void pm_runtime_drop_link(struct device *dev)
 {
+	rpm_put_suppliers(dev);
+
 	spin_lock_irq(&dev->power.lock);
 	WARN_ON(dev->power.links_count == 0);
 	dev->power.links_count--;
-- 
2.7.4

Re: [PATCH] PM / runtime: Drop usage count for suppliers at device link removal

[Rafael J. Wysocki]

On Thu, May 24, 2018 at 10:33 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> In the case consumer device is runtime resumed, while the link to the
> supplier is removed, the earlier call to pm_runtime_get_sync() made from
> rpm_get_suppliers() does not get properly balanced with a corresponding
> call to pm_runtime_put(). This leads to that suppliers remains to be
> runtime resumed forever, while they don't need to.
>
> Let's fix the behaviour by calling rpm_put_suppliers() when dropping a
> device link. Not that, since rpm_put_suppliers() checks the
> link->rpm_active flag, we can correctly avoid to call pm_runtime_put() in
> cases when we shouldn't.
>
> Reported-by: Todor Tomov <todor.tomov@linaro.org>
> Fixes: 21d5c57b3726 ("PM / runtime: Use device links")
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
>
> Rafael, I am not sure if this is safe from locking point of view. The device
> link write lock has been taken when pm_runtime_drop_link() is called, hence I
> assume calling rpm_put_suppliers() should be fine!? If not, can you please
> advise how to change?

Holding the lock should be sufficient for the list to be stable, so
AFAICS it is OK.

Thanks,
Rafael

Re: [PATCH] PM / runtime: Drop usage count for suppliers at device link removal

[Rafael J. Wysocki]

On Sunday, May 27, 2018 12:18:05 PM CEST Rafael J. Wysocki wrote:
> On Thu, May 24, 2018 at 10:33 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > In the case consumer device is runtime resumed, while the link to the
> > supplier is removed, the earlier call to pm_runtime_get_sync() made from
> > rpm_get_suppliers() does not get properly balanced with a corresponding
> > call to pm_runtime_put(). This leads to that suppliers remains to be
> > runtime resumed forever, while they don't need to.
> >
> > Let's fix the behaviour by calling rpm_put_suppliers() when dropping a
> > device link. Not that, since rpm_put_suppliers() checks the
> > link->rpm_active flag, we can correctly avoid to call pm_runtime_put() in
> > cases when we shouldn't.
> >
> > Reported-by: Todor Tomov <todor.tomov@linaro.org>
> > Fixes: 21d5c57b3726 ("PM / runtime: Use device links")
> > Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> > ---
> >
> > Rafael, I am not sure if this is safe from locking point of view. The device
> > link write lock has been taken when pm_runtime_drop_link() is called, hence I
> > assume calling rpm_put_suppliers() should be fine!? If not, can you please
> > advise how to change?
> 
> Holding the lock should be sufficient for the list to be stable, so
> AFAICS it is OK.

So the patch has been applied, thanks!