linux-kernel - Re: [PATCH] proc: fixup map

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Date:   Sun, 11 Nov 2018 00:48:47 -0200
From:   Rafael David Tinoco <rafael.tinoco@...aro.org>
To:     Alexey Dobriyan <adobriyan@...il.com>, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, gorcunov@...il.com,
        linux-kselftest@...r.kernel.org, shuah@...nel.org
Subject: Re: [PATCH] proc: fixup map_files test on arm

Including Shuah and kselftest list...

On Sat, Nov 10, 2018, at 4:49 PM, Alexey Dobriyan wrote:
> https://bugs.linaro.org/show_bug.cgi?id=3782
> 
> Turns out arm doesn't allow to map address 0, so try minimum virtual
> address instead.
> 
> Reported-by: Rafael David Tinoco <rafael.tinoco@...aro.org>
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> 
>  tools/testing/selftests/proc/proc-self-map-files-002.c |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> --- a/tools/testing/selftests/proc/proc-self-map-files-002.c
> +++ b/tools/testing/selftests/proc/proc-self-map-files-002.c
> @@ -13,7 +13,7 @@
>   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT 
> OF
>   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
>   */
> -/* Test readlink /proc/self/map_files/... with address 0. */
> +/* Test readlink /proc/self/map_files/... with minimum address. */
>  #include <errno.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
> @@ -47,6 +47,11 @@ static void fail(const char *fmt, unsigned long a, 
> unsigned long b)
>  int main(void)
>  {
>  	const unsigned int PAGE_SIZE = sysconf(_SC_PAGESIZE);
> +#ifdef __arm__
> +	unsigned long va = 2 * PAGE_SIZE;
> +#else
> +	unsigned long va = 0;
> +#endif
>  	void *p;
>  	int fd;
>  	unsigned long a, b;
> @@ -55,7 +60,7 @@ 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(va, PAGE_SIZE, PROT_NONE, MAP_PRIVATE|MAP_FILE|MAP_FIXED, fd, 0);
>  	if (p == MAP_FAILED) {
>  		if (errno == EPERM)
>  			return 2;

I have sent a patch removing proc-self-map-files-002 AND making 001 to use as a
HINT for mmap (MAP_FIXED) *at least*  *(2 * PAGE_SIZE), which would, likely,
attend all  architectures, avoiding trying to make the test specific to one,
and, still, test the symlinks for issues (like bad chars, spaces, so on).

Both tests (001 and 002) have pretty much the same code, while they could have 2
tests in a single code, using kselftest framework. Is NULL hint + MAP_FIXED
something imperative for this test ? Why not to have all in a single test ? Are
you keeping the NULL hint just to test mmap, apart" from the core of this test ?

Sorry to insist.. If you want to keep it like this, I can create a similar test
in LTP - for the symlinks only, which seem important - and blacklist this one in
our function tests kselftest list (https://lkft.linaro.org/), then no change is
needed on your side.

Thanks