linux-kernel - Re: selftests/vm madv

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Message-ID: <77f4c6a9-141d-e103-7339-0055cc00f752@redhat.com>
Date:   Fri, 15 Oct 2021 18:06:13 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: selftests/vm madv_populate.c test

On 15.10.21 17:47, David Hildenbrand wrote:
> On 15.10.21 17:45, Shuah Khan wrote:
>> On 9/18/21 1:41 AM, David Hildenbrand wrote:
>>> On 18.09.21 00:45, Shuah Khan wrote:
>>>> Hi David,
>>>>
>>>> I am running into the following warning when try to build this test:
>>>>
>>>> madv_populate.c:334:2: warning: #warning "missing MADV_POPULATE_READ or MADV_POPULATE_WRITE definition" [-Wcpp]
>>>>     334 | #warning "missing MADV_POPULATE_READ or MADV_POPULATE_WRITE definition"
>>>>         |  ^~~~~~~
>>>>
>>>>
>>>> I see that the following handling is in place. However there is no
>>>> other information to explain why the check is necessary.
>>>>
>>>> #if defined(MADV_POPULATE_READ) && defined(MADV_POPULATE_WRITE)
>>>>
>>>> #else /* defined(MADV_POPULATE_READ) && defined(MADV_POPULATE_WRITE) */
>>>>
>>>> #warning "missing MADV_POPULATE_READ or MADV_POPULATE_WRITE definition"
>>>>
>>>> I do see these defined in:
>>>>
>>>> include/uapi/asm-generic/mman-common.h:#define MADV_POPULATE_READ       22
>>>> include/uapi/asm-generic/mman-common.h:#define MADV_POPULATE_WRITE      23
>>>>
>>>> Is this the case of missing include from madv_populate.c?
>>>
>>> Hi Shuan,
>>>
>>> note that we're including "#include <sys/mman.h>", which in my
>>> understanding maps to the version installed on your system instead
>>> of the one in our build environment.ing.
>>>
>>> So as soon as you have a proper kernel + the proper headers installed
>>> and try to build, it would pick up MADV_POPULATE_READ and
>>> MADV_POPULATE_WRITE from the updated headers. That makes sense: you
>>> annot run any MADV_POPULATE_READ/MADV_POPULATE_WRITE tests on a kernel
>>> that doesn't support it.
>>>
>>> See vm/userfaultfd.c where we do something similar.
>>>
>>
>> Kselftest is for testing the kernel with kernel headers. That is the
>> reason why there is the dependency on header install.
>>
>>>
>>> As soon as we have a proper environment, it seems to work just fine:
>>>
>>> Linux vm-0 5.15.0-0.rc1.20210915git3ca706c189db.13.fc36.x86_64 #1 SMP Thu Sep 16 11:32:54 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
>>> [root@...0 linux]# cat /etc/redhat-release
>>> Fedora release 36 (Rawhide)
>>
>> This is a distro release. We don't want to have dependency on headers
>> from the distro to run selftests. Hope this makes sense.
>>
>> I still see this on my test system running Linux 5.15-rc5.
> 
> Did you also install Linux headers? I assume no, correct?
> 

What happens in your environment when compiling and running the
memfd_secret test?

If assume you'll see a "skip" when executing, because it might also
refer to the local version of linux headers and although it builds, it
really cannot build something "functional". It just doesn't add a
"#warning" to make that obvious.

-- 
Thanks,

David / dhildenb