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

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Hello, Roman.

On Thu, Aug 11, 2016 at 11:07:14AM +0200, Roman Penyaev wrote:
> Yes, exactly, this is an illegal operation.  But it is not more illegal
> than calling kill() twice or reinit() when counter is not yet zero.
> And those illegals are covered with warnings, which can be observed
> for example with this freeze/unfreeze blk-mq bug.

I have no objections about adding warnings for these conditions;
however, adding rcu barrier to mask illegal usages is a very different
thing.  That adds a lot of unnecessary latency to the exit function
and makes it unusable from non-sleepable contexts.

Thanks.

-- 
tejun

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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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