Re: [PATCH v3] CPU hotplug: active_writer not woken up in some cases - deadlock

From: Oleg Nesterov
Date: Tue Dec 09 2014 - 20:20:26 EST

On 12/09, Paul E. McKenney wrote:
> Would wait_event()/wake_up() work for the wakeup-writer case?

Yes, and in this case we could probably kill this puts_pending logic
and avoid cpu_hotplug.lock in put_online_cpus() altogether? Can't we
just make cpu_hotplug.refcount atomic_t?

Anyway, this makes me think again that this code should use percpu_rwsem.
Perhaps I'll try to make a patch next week...

(we need down_write_recursive_readers(), and probably rcusync patches).


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