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SubjectRe: [PATCH v6 4/5] PM / runtime: Use device links
On Sun, Dec 18, 2016 at 5:37 PM, Lukas Wunner <lukas@wunner.de> wrote:
> On Sun, Dec 18, 2016 at 04:53:26PM +0100, Rafael J. Wysocki wrote:
>> On Sun, Dec 18, 2016 at 3:01 PM, Lukas Wunner <lukas@wunner.de> wrote:
>> > Hi Rafael,
>> >
>> > spotted what looks like a bug in the device links runtime PM code:
>> >
>> > When resuming a device, __rpm_callback() calls rpm_get_suppliers(dev):
>> >
>> >> + retval = rpm_get_suppliers(dev);
>> >> + if (retval)
>> >> + goto fail;
>> >
>> >
>> > This will walk the list of suppliers and call pm_runtime_get_sync()
>> > for each of them:
>> >
>> >> +static int rpm_get_suppliers(struct device *dev)
>> >> +{
>> >> + struct device_link *link;
>> >> +
>> >> + list_for_each_entry_rcu(link, &dev->links.suppliers, c_node) {
>> >> + int retval;
>> > [...]
>> >> + retval = pm_runtime_get_sync(link->supplier);
>> >> + if (retval < 0) {
>> >> + pm_runtime_put_noidle(link->supplier);
>> >> + return retval;
>> >
>> >
>> > If pm_runtime_get_sync() failed, e.g. because runtime PM is disabled
>> > on a supplier, the function will put the reference of the failed
>> > supplier and return.
>> >
>> > Back in __rpm_callback() we jump to the fail mark, where we call
>> > rpm_put_suppliers().
>> >
>> >> + fail:
>> >> + rpm_put_suppliers(dev);
>> >> +
>> >> + device_links_read_unlock(idx);
>> >
>> >
>> > This walks the list of suppliers and releases a ref for each of them:
>> >
>> >> +static void rpm_put_suppliers(struct device *dev)
>> >> +{
>> >> + struct device_link *link;
>> >> +
>> >> + list_for_each_entry_rcu(link, &dev->links.suppliers, c_node)
>> >> + if (link->rpm_active &&
>> >> + READ_ONCE(link->status) != DL_STATE_SUPPLIER_UNBIND) {
>> >> + pm_runtime_put(link->supplier);
>> >> + link->rpm_active = false;
>> >> + }
>> >> +}
>> >
>> >
>> > This looks wrong: We've already put a ref on the failed supplier, so here
>> > we're putting another one.
>>
>> Are we? I would think link->rpm_active would be false for the failed
>> one, wouldn't it?
>
> Ah, so link->rpm_active means the consumer is holding a ref on the supplier.

Yes, that's the idea. :-)

> Missed that, sorry for the false alarm and thanks for the clarification.

No problem.

Thanks,
Rafael

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