linux-kernel - Re: WARN @lib/refcount.c:128 during hot unplug of I/O adapter.

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Message-Id: <89aec36c-e352-e055-5e80-1235449762ce@linux.vnet.ibm.com>
Date:   Mon, 10 Apr 2017 10:53:08 -0700
From:   Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Sachin Sant <sachinp@...ux.vnet.ibm.com>,
        linuxppc-dev@...abs.org
Cc:     Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: WARN @lib/refcount.c:128 during hot unplug of I/O adapter.

On 04/06/2017 09:04 PM, Michael Ellerman wrote:
> Tyrel Datwyler <tyreld@...ux.vnet.ibm.com> writes:
> 
>> On 04/06/2017 03:27 AM, Sachin Sant wrote:
>>> On a POWER8 LPAR running 4.11.0-rc5, a hot unplug operation on
>>> any I/O adapter results in the following warning
>>>
>>> This problem has been in the code for some time now. I had first seen this in
>>> -next tree.
>>>

<snip>

>>> Have attached the dmesg log from the system. Let me know if any additional
>>> information is required to help debug this problem.
>>
>> I remember you mentioning this when the issue was brought up for CPUs. I
>> assume the case is the same here where the issue is only seen with
>> adapters that were hot-added after boot (ie. hot-remove of adapter
>> present at boot doesn't trip the warning)?
> 
> So who's fixing this?

I started looking at it when Bharata submitted a patch trying to fix the
issue for CPUs, but got side tracked by other things. I suspect that
this underflow has actually been an issue for quite some time, and we
are just now becoming aware of it thanks to the recount_t patchset being
merged. I'll look into it again this week.

-Tyrel

> 
> cheers
>