linux-kernel - Re: [PATCH] proc: fix proc-self-map-files selftest for arm

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Date:   Thu, 11 Oct 2018 22:42:10 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Rafael David Tinoco <rafael.tinoco@...aro.org>
Cc:     linux-kselftest@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        shuah@...nel.org, adobriyan@...il.com
Subject: Re: [PATCH] proc: fix proc-self-map-files selftest for arm

On Thu, Oct 11, 2018 at 03:43:59PM -0300, Rafael David Tinoco wrote:
> MAP_FIXED is important for this test but, unfortunately, lowest virtual
> address for user space mapping on arm is (PAGE_SIZE * 2) and NULL hint
> does not seem to guarantee that when MAP_FIXED is given. This patch sets
> the virtual address that will hold the mapping for the test, fixing the
> issue.
> 
> Link: https://bugs.linaro.org/show_bug.cgi?id=3782
> Signed-off-by: Rafael David Tinoco <rafael.tinoco@...aro.org>
> ---
>  tools/testing/selftests/proc/proc-self-map-files-002.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/proc/proc-self-map-files-002.c b/tools/testing/selftests/proc/proc-self-map-files-002.c
> index 6f1f4a6e1ecb..0a47eaca732a 100644
> --- a/tools/testing/selftests/proc/proc-self-map-files-002.c
> +++ b/tools/testing/selftests/proc/proc-self-map-files-002.c
> @@ -55,7 +55,9 @@ int main(void)
>  	if (fd == -1)
>  		return 1;
>  
> -	p = mmap(NULL, PAGE_SIZE, PROT_NONE, MAP_PRIVATE|MAP_FILE|MAP_FIXED, fd, 0);
> +	p = mmap((void *) (2 * PAGE_SIZE), PAGE_SIZE, PROT_NONE,
> +			MAP_PRIVATE|MAP_FILE|MAP_FIXED, fd, 0);
> +
>  	if (p == MAP_FAILED) {
>  		if (errno == EPERM)
>  			return 2;

As far as I remember nil virtual address has been there only to be sure the
vma allocated won't be merged with another vmas. Fore sure most of x86
standart application won't be using 8K address as well, so should do the
trick I think.

(Strictlly speaking the test should be rather parsing own maps first and
 find unused address instead but whatever :)

Reviewed-by: Cyrill Gorcunov <gorcunov@...il.com>