linux-kernel - Re: PROBLEM: selftest/vm/cow.c failed to compile (‘MADV

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Message-ID: <dda726db-6276-f312-be12-cee05228161d@alu.unizg.hr>
Date:   Tue, 10 Jan 2023 13:25:24 +0100
From:   Mirsad Todorovac <mirsad.todorovac@....unizg.hr>
To:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: PROBLEM: selftest/vm/cow.c failed to compile (‘MADV_PAGEOUT’ undeclared)

On 1/10/23 11:05, David Hildenbrand wrote:
> On 09.01.23 22:41, Mirsad Goran Todorovac wrote:
>> On 1/9/2023 5:42 PM, David Hildenbrand wrote:
>>
>> Hi, thank you for your reply.
>>
>>>> I hope this is enough information for you to debug the issue.
>>>>
>>>> I am standing by for any additional diagnostics needed.
>>>
>>> Won't userfaultfd.c fail in a similar way?
>>>
>>> Anyhow, khugepaged.c jas
>>>
>>> #ifndef MADV_PAGEOUT
>>> #define MADV_PAGEOUT 21
>>> #endif
>>>
>>> So most probably we should do the same.
>>
>> Actually, David, it turned out that userfaultfd.c compiled
>> out-of-the-box, and side-by-side comparison showed that it also included
>> "/home/marvin/linux/kernel/linux_torvalds/usr/include/asm-generic/mman-common.h"
>>
>> The only remaining difference was including <linux/mman.h>, which fixed
>> the issue w/o #ifdef ... #endif
>>
>> Hope this helps.
>>
>> Please find the following diff.
>>
>> Regards,
>> Mirsad
>>
>> ------------------------------------------------------------------------------
>> diff --git a/tools/testing/selftests/vm/cow.c
>> b/tools/testing/selftests/vm/cow.c
>> index 26f6ea3079e2..dd8cf12c6776 100644
>> --- a/tools/testing/selftests/vm/cow.c
>> +++ b/tools/testing/selftests/vm/cow.c
>> @@ -16,6 +16,7 @@
>>    #include <fcntl.h>
>>    #include <dirent.h>
>>    #include <assert.h>
>> +#include <linux/mman.h>
>>    #include <sys/mman.h>
>>    #include <sys/ioctl.h>
>>    #include <sys/wait.h>
>>
> 
> I already sent a different fix [1]. I suspect when including
> linux/mman.h, it would still be problematic with older kernel
> headers that lack MADV_PAGEOUT (< v5.4).

I see your point.

> But yeah, I saw that userfaultfd.c was fixed that way:
> 
> commit b773827e361952b3f53ac6fa4c4e39ccd632102e
> Author: Chengming Zhou <zhouchengming@...edance.com>
> Date:   Fri Mar 4 20:29:04 2022 -0800
> 
>      kselftest/vm: fix tests build with old libc
>      The error message when I build vm tests on debian10 (GLIBC 2.28):
>          userfaultfd.c: In function `userfaultfd_pagemap_test':
>          userfaultfd.c:1393:37: error: `MADV_PAGEOUT' undeclared (first use
>          in this function); did you mean `MADV_RANDOM'?
>            if (madvise(area_dst, test_pgsize, MADV_PAGEOUT))
>                                               ^~~~~~~~~~~~
>                                               MADV_RANDOM
>      This patch includes these newer definitions from UAPI linux/mman.h, is
>      useful to fix tests build on systems without these definitions in 
> glibc
>      sys/mman.h.
> 
> 
> [1] https://lkml.kernel.org/r/20230109171255.488749-1-david@redhat.com

You're the boss :)

However, IMHO, having MADV_PAGEOUT defined in three or four places could
make like miserable. OK, it is unlikely to change value, but something
tells me that the right way to do it is to guarantee that the macro
definition is unique.

I don't know what would be the right thing to do in pre-5.4 kernels
w/o MADV_PAGEOUT defined.

Probably then the "(madvise(area_dst, test_pgsize, MADV_PAGEOUT)" gives
EINVAL or is undefined?

-- 
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu

System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia