linux-kernel - Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu

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Message-ID: <20160811162901.GC2695@mtj.duckdns.org>
Date:	Thu, 11 Aug 2016 12:29:01 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Roman Penyaev <roman.penyaev@...fitbricks.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier()
 just before freeing

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