Messages in this thread | | | Date | Tue, 9 Dec 2014 19:18:09 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v3] CPU hotplug: active_writer not woken up in some cases - deadlock |
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On Wed, Dec 10, 2014 at 01:26:19AM +0100, Oleg Nesterov wrote: > 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?
Seems like that should be possible. That would certainly simplify the wakeup logic from put_online_cpus(). It might even be possible to avoid acquiring cpu_hotplug.lock in put_online_cpus(), though that would of course require more luck than anyone deserves.
> 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).
Careful! You might end up re-introducing the deadlock that I used puts_pending to get rid of. ;-)
Thanx, Paul
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