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

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Date:   Tue, 11 Apr 2017 19:00:08 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        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.

Tyrel Datwyler <tyreld@...ux.vnet.ibm.com> writes:

> 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.

Yes I agree. Which means it might be broken in existing distros.

> I'll look into it again this week.

Thanks.

cheers