Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

From: David Hildenbrand
Date: Mon Dec 08 2014 - 14:30:29 EST

> > active_writer is cleared while holding cpuhp_lock, so this should be safe,
> > right?
> You lost me on that one. Don't we get to that piece of code precisely
> because we don't hold any of the CPU-hotplug locks? If so, the
> writer might well hold all the locks it needs, and might well change
> cpu_hotplug.active_writer out from under us.
> What am I missing here?
> Thanx, Paul

I was missing that cpuhp_lock_* are simply lockdep anotations ... it's
getting late :)

So you're right, we need to verify that we don't get a 0 on the second access.

Will send an updated version soon.


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