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Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier() just before freeing

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On Wed, Aug 10, 2016 at 09:55:39PM +0200, Roman Pen wrote:
> percpu issues some RCU callbacks to synchronize its state, so before
> freeing we have to wait all those callbacks to finish.
> 
> E.g. the following simple sequence on stack causes nasty crash:
> 
>     struct percpu_ref ref;
> 
>     percpu_ref_init(&ref, release, 0, GFP_KERNEL);
>     percpu_ref_kill(&ref);
>     percpu_ref_exit(&ref);

Hmmm... that's just an illegal sequence of operations.  You can't exit
a ref which hasn't completed killing yet (the kill callback hasn't
been called).

Thanks.

-- 
tejun

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[PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier() just before freeing Roman Pen <roman.penyaev@profitbricks.com> - 2016-08-10 22:00 +0200
  Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier()  just before freeing Tejun Heo <tj@kernel.org> - 2016-08-11 00:10 +0200
    Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier()  just before freeing Roman Penyaev <roman.penyaev@profitbricks.com> - 2016-08-11 11:10 +0200
      Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier()  just before freeing Tejun Heo <tj@kernel.org> - 2016-08-11 18:30 +0200
        Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier()  just before freeing Roman Penyaev <roman.penyaev@profitbricks.com> - 2016-08-11 19:40 +0200

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