Re: WARNING: suspicious RCU usage - sdhci-pltfm: SDHCI platform and OF driver helper

[Ulf Hansson]

On Wed, 2 Sep 2020 at 14:14, <peterz@xxxxxxxxxxxxx> wrote:
>
> On Wed, Sep 02, 2020 at 09:03:37AM +0200, Ulf Hansson wrote:
> > Lots of cpuidle drivers are using CPU_PM notifiers (grep for
> > cpu_pm_enter and you will see) from their idlestates ->enter()
> > callbacks. And for those we are already calling
> > rcu_irq_enter_irqson|off() in cpu_pm_notify() when firing them.
>
> Yeah, that particular trainwreck is on my todo list already ... then
> again, that list is forever overflowing.
>
> I'm thinking cpu_pm_unregister_notifier() is not a common thing? The few
> I looked at seem to suggest 'never' is a good approximation.

The trend is that drivers are turning into regular modules that may
also need to manage "->remove()", which may mean unregistering the
notifier. Of course, I don't know for sure whether that becomes a
problem, but it seems quite limiting.

>
> It would be fairly trivial to replace the atomic_notifier usage with a
> raw_notifier a lock and either stop-machine or IPIs. Better still would
> be if we can get rid of it entirely, but I can't tell in a hurry if that
> is possible.

Okay, let's see.

In any case, I was thinking that the patch with CPU idle flag, for
letting CPU idle drivers deal with RCU, that you proposed, seems like
a good first step.

At least it should enable us to solve the problem for runtime PM in
psci_enter_domain_idle_state(). Let me update the patch and send it
out, then we can continue the discussion over there.

Kind regards
Uffe