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    SubjectRe: [PATCH v6 4/5] PM / runtime: Use device links
    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?

    > And if there are further suppliers in the list
    > following the failed one, we'll decrement their refcount even though we've
    > never incremented it.

    I'm not following you here, sorry.

    Thanks,
    Rafael

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