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

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Message-ID: <CAJrWOzD5U6f9skNEWRvJjRe01EF1s=aESM_Qe+PjVar_Z98=-Q@mail.gmail.com>
Date:	Thu, 11 Aug 2016 19:29:34 +0200
From:	Roman Penyaev <roman.penyaev@...fitbricks.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier()
 just before freeing

Hi,

On Thu, Aug 11, 2016 at 6:29 PM, Tejun Heo <tj@...nel.org> wrote:
> 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.
>

Yes, for sure that makes sense.  I changed the patch a little.
Have sent.

--
Roman