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Date:   Mon, 31 Jan 2022 15:00:23 -0800
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Subject: Re: [PATCH] userfaultfd/selftests: use swap() to make code cleaner
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To:     cgel.zte@gmail.com, akpm@linux-foundation.org
Cc:     shuah@kernel.org, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
        Changcheng Deng <deng.changcheng@zte.com.cn>,
        Zeal Robot <zealci@zte.com.cn>
References: <20211028112331.16152-1-deng.changcheng@zte.com.cn>
From:   Mike Kravetz <mike.kravetz@oracle.com>
In-Reply-To: <20211028112331.16152-1-deng.changcheng@zte.com.cn>
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On 10/28/21 04:23, cgel.zte@gmail.com wrote:
> From: Changcheng Deng <deng.changcheng@zte.com.cn>
> 
> Use swap() in order to make code cleaner. Issue found by coccinelle.
> 
> Reported-by: Zeal Robot <zealci@zte.com.cn>
> Signed-off-by: Changcheng Deng <deng.changcheng@zte.com.cn>
> ---
>  tools/testing/selftests/vm/userfaultfd.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
> index 8a09057d2f22..41dfe6f4ebfb 100644
> --- a/tools/testing/selftests/vm/userfaultfd.c
> +++ b/tools/testing/selftests/vm/userfaultfd.c
> @@ -1413,7 +1413,6 @@ static void userfaultfd_pagemap_test(unsigned int test_pgsize)
>  static int userfaultfd_stress(void)
>  {
>  	void *area;
> -	char *tmp_area;
>  	unsigned long nr;
>  	struct uffdio_register uffdio_register;
>  	struct uffd_stats uffd_stats[nr_cpus];
> @@ -1524,13 +1523,8 @@ static int userfaultfd_stress(void)
>  					    count_verify[nr], nr);
>  
>  		/* prepare next bounce */
> -		tmp_area = area_src;
> -		area_src = area_dst;
> -		area_dst = tmp_area;
> -
> -		tmp_area = area_src_alias;
> -		area_src_alias = area_dst_alias;
> -		area_dst_alias = tmp_area;
> +		swap(area_src, area_dst);
> +		swap(area_src_alias, area_dst_alias);
>  
>  		uffd_stats_report(uffd_stats, nr_cpus);
>  	}

Sorry for the late comment/question.

Where is the test supposed to get the definition of swap()?  When trying to
build, I get:

gcc -Wall -I ../../../../usr/include  -no-pie    userfaultfd.c -lrt -lpthread -o /home/mkravetz/tmp/linux-stable/tools/testing/selftests/vm/userfaultfd
userfaultfd.c: In function ‘userfaultfd_stress’:
userfaultfd.c:1530:3: warning: implicit declaration of function ‘swap’; did you mean ‘swab’? [-Wimplicit-function-declaration]
 1530 |   swap(area_src, area_dst);
      |   ^~~~
      |   swab
/usr/bin/ld: /tmp/ccPiwPM0.o: in function `userfaultfd_stress':
userfaultfd.c:(.text+0x4b6d): undefined reference to `swap'
/usr/bin/ld: userfaultfd.c:(.text+0x4b8b): undefined reference to `swap'
collect2: error: ld returned 1 exit status
make[1]: *** [../lib.mk:146: /home/mkravetz/tmp/linux-stable/tools/testing/selftests/vm/userfaultfd] Error 1

As far as I can see, swap is only defined in 'include/linux/minmax.h'.
However, that is not part of the user API and not available to the tests.
What am I missing?
--
Mike Kravetz