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Subject: Re: [PATCH v3] LoongArch: Add support to clone a time namespace
To:     Tiezhu Yang <yangtiezhu@loongson.cn>
References: <1685519761-20425-1-git-send-email-yangtiezhu@loongson.cn>
 <87bki0hn4y.ffs@tglx> <d9684f7b-871a-e759-d6b8-4556719702a1@loongson.cn>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>,
        Christian Brauner <brauner@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
        loongson-kernel@lists.loongnix.cn
From:   Youling Tang <tangyouling@loongson.cn>
Message-ID: <cc45475e-3d87-efa5-1c3a-c2c70d6aca94@loongson.cn>
Date:   Sat, 3 Jun 2023 10:07:50 +0800
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Hi, Tiezhu

On 05/31/2023 06:04 PM, Tiezhu Yang wrote:
>
>
> On 05/31/2023 05:21 PM, Thomas Gleixner wrote:
>> On Wed, May 31 2023 at 15:56, Tiezhu Yang wrote:
>>> When execute the following command to test clone3 on LoongArch:
>>>
>>>   # cd tools/testing/selftests/clone3 && make && ./clone3
>>>
>>> we can see the following error info:
>>>
>>>   # [5719] Trying clone3() with flags 0x80 (size 0)
>>>   # Invalid argument - Failed to create new process
>>>   # [5719] clone3() with flags says: -22 expected 0
>>>   not ok 18 [5719] Result (-22) is different than expected (0)
>>>
>>> This is because if CONFIG_TIME_NS is not set, but the flag
>>> CLONE_NEWTIME (0x80) is used to clone a time namespace, it
>>> will return -EINVAL in copy_time_ns().
>>
>> Which means that test case is broken.
>>
>>> With this patch, the following failed test can be fixed too:
>>
>> You cannot fix a broken test case by enabling functionality which
>> is not guaranteed to be available on all platforms.
>>
>> Adding time name spaces on loongarch is a completely separate issue and
>> has absolutely nothing to do with broken test cases.
>>
>> They are still broken when CONFIG_TIME_NS is disabled in Kconfig, no?
>>
>> So this wants to be two separate things:
>>
>>    1) Fix the broken test cases so they handle CONFIG_TIME_NS=n
>>       situations correctly
>>
>>    2) Add support for TIME_NS to loongarch
>>

With this patch, we should also modify the stack_top() implementation,
because the vvar size is not PAGE_SIZE at this time.

'maps' before the patch,
  # sudo cat /proc/1/maps
  ...
  7ffffbec8000-7ffffbeec000 rw-p 00000000 00:00 0 
   [stack]
  7ffffc7d8000-7ffffc7dc000 r--p 00000000 00:00 0 
   [vvar]
  7ffffc7dc000-7ffffc7e0000 r-xp 00000000 00:00 0 
   [vdso]

STACK_TOP = TASK_SIZE - PAGE_ALIGN(current->thread.vdso->size) - VVAR_SIZE

Thanks,
Youling.

>
>
> Thanks for your reply and detailed suggestions,
> I will do it in the next version.
>
> Thanks,
> Tiezhu
>