linux-kernel - Re: [PATCH] kunit: tool: Force the use of the 'tty' console for UML

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Message-ID: <578de82c-5119-78e4-4497-c8a8d642388d@linuxfoundation.org>
Date:   Thu, 7 Jan 2021 11:13:54 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Petr Mladek <pmladek@...e.com>, David Gow <davidgow@...gle.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] kunit: tool: Force the use of the 'tty' console for UML

On 1/7/21 9:53 AM, Petr Mladek wrote:
> On Wed 2021-01-06 12:29:12, David Gow wrote:
>> On Wed, Jan 6, 2021 at 3:52 AM Shuah Khan <skhan@...uxfoundation.org> wrote:
>>>
>>> On 1/5/21 11:57 AM, Andy Shevchenko wrote:
>>>> On Tue, Jan 05, 2021 at 09:34:33AM -0700, Shuah Khan wrote:
>>>>> On 1/5/21 9:21 AM, Petr Mladek wrote:
>>>>>> On Mon 2021-01-04 09:23:57, Shuah Khan wrote:
>>>>>>> On 12/22/20 4:11 AM, Andy Shevchenko wrote:
>>>>>>>> On Mon, Dec 21, 2020 at 11:39:00PM -0800, David Gow wrote:
>>>>>>>>> kunit_tool relies on the UML console outputting printk() output to the
>>>>>>>>> tty in order to get results. Since the default console driver could
>>>>>>>>> change, pass 'console=tty' to the kernel.
>>>>>>>>>
>>>>>>>>> This is triggered by a change[1] to use ttynull as a fallback console
>>>>>>>>> driver which -- by chance or by design -- seems to have changed the
>>>>>>>>> default console output on UML, breaking kunit_tool. While this may be
>>>>>>>>> fixed, we should be less fragile to such changes in the default.
>>>>>>>>>
>>>>>>>>> [1]:
>>>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=757055ae8dedf5333af17b3b5b4b70ba9bc9da4e
>>>>>>>>
>>>>>>>> Reported-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>>>>>>>> Tested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>>>>>>>>
>>>>>>>
>>>>>>> Thank you all. Now in linux-kselftest kunit-fixes branch.
>>>>>>>
>>>>>>> Will send this up for rc3.
>>>>>>>
>>>>>>> Sorry for the delay - have been away from the keyboard for a
>>>>>>> bit.
>>>>>>
>>>>>> JFYI, I am not sure that this is the right solution. I am
>>>>>> looking into it, see
>>>>>> https://lore.kernel.org/linux-kselftest/X%2FSRA1P8t+ONZFKb@alley/
>>>>>> for more details.
>>>>>>
>>>>>
>>>>> Thanks Petr. I will hold off on sending the patch up to Linus and
>>>>> let you find a the right solution.
>>>>
>>>> Please. leave it in Linux Next at least. Otherwise kunit will be broken for a
>>>> long time which is not good.
>>>>
>>>>
>>>
>>> Yes. That is the plan. It will be in there until real fix comes in.
> 
> The real fix would be too complicated for 5.11-rc3. Instead, I
> proposed to revert the problematic commit, see
> https://lore.kernel.org/lkml/20210107164400.17904-2-pmladek@suse.com/
> I would like to push it for 5.11-rc3.
> 
>> Personally, I think that this patch makes some sense to keep even if
>> the underlying issue with ttynull is resolved. Given that kunit.py
>> requires the console output, explicitly stating we want console=tty
>> set is probably worth doing rather than relying on it being the
>> default.
> 
> I agree that the patch makes sense on its own. kunit depends on the
> particular console. Note that "tty" is actually the UML-specific
> stdio console implemented in arch/um/drivers/stdio_console.c.
> 

The proposal sounds like revert the problem commit 
https://lore.kernel.org/lkml/20210107164400.17904-2-pmladek@suse.com/

and also send kunit fix up. Sounds reasonable to me. I will send
it for 5.11-rc3

thanks,
-- Shuah