linux-kernel - Re: [RFC PATCH] ACPICA: Tables: Fix regression introduced by a too early mechanism enabling

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Date:   Wed, 26 Apr 2017 08:34:26 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Zheng, Lv" <lv.zheng@...el.com>
Cc:     "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        "Brown, Len" <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [RFC PATCH] ACPICA: Tables: Fix regression introduced by a too
 early mechanism enabling

On Wed, Apr 26, 2017 at 7:13 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Tue, Apr 25, 2017 at 10:15 PM, Zheng, Lv <lv.zheng@...el.com> wrote:
>> Hi,
>>
>>> From: Dan Williams [mailto:dan.j.williams@...el.com]
>>> Subject: Re: [RFC PATCH] ACPICA: Tables: Fix regression introduced by a too early mechanism enabling
>>>
>>> On Tue, Apr 25, 2017 at 6:49 PM, Lv Zheng <lv.zheng@...el.com> wrote:
>>> > In the Linux kernel side, acpi_get_table() hasn't been fully balanced by
>>> > acpi_put_table() invocations. So it is not a good timing to report errors.
>>> > The strict balanced validation count check should only be enabled after
>>> > confirming that all kernel side invocations are safe.
>>>
>>> We've been living with this bug for 7 years, let's just go fix all
>>> acpi_get_table() invocations to make sure they have a corresponding
>>> acpi_put_table().
>>
>> We knew that, you should have already seen a series internally or
>> externally from me achieving this.
>> It's done several years ago. But it takes long time to make the
>> ACPICA part upstreamed.
>>
>> Now my plan is:
>> 1. introduce the APIs but allow old usage models in order not to
>>    change old ACPICA behavior and its users.
>> 2. fix all users
>> 3. disallow old usage models.
>> It's just my mistake to leak the final stage approach to the ACPICA
>> upstream from my local repo.
>> Now we can try to jump to the final step, but as far as I know,
>> not only Linux, ACPICA itself also contains several broken cases.
>>
>> Bottom line of Linux kernel is we shouldn't break any running system.
>> So IMO, we will need this commit during this special period.
>>
>> I didn't say the final step is wrong or is not required.
>> We can do both in parallel.
>>
>> So could you please help to confirm if it's working.
>> And I would like to suggest linux to take this first step fix along
>> with other final step fixes during this period.
>
> I just think "this period" is very short and we can skip the band-aid
> and go straight to auditing the 48 call sites of acpi_get_table.

Moreover, I don't think this workaround is a workable approach because
it leaves the ACPI_ERROR() in place to continue to spam the logs.