Re: [LTP] [PATCH] max_map_count: corrected max_map_count condition

[Caspar Zhang <caspar@casparzhang.com>]

On 07/30/2013 09:47 PM, Stanislav Kholmanskikh wrote:
> From: Stanislav kholmanskikh <stanislav.kholmanskikh@oracle.com>
>
> * kernel test for max_map_count_sysctl is:
>     /* Too many mappings? */
>     if (mm->map_count > sysctl_max_map_count)
>       return -ENOMEM;
>    so in LTP test map_count should be greater than max_map_count by 1
>
> * only [vsyscall] is allocated without incrementing mm->map_count
>
> Author: Bob Picco <bob.picco@oracle.com>
>
> Signed-off-by: Stanislav kholmanskikh <stanislav.kholmanskikh@oracle.com>

Acked-by: Caspar Zhang <caspar@casparzhang.com>

> ---
>   testcases/kernel/mem/tunable/max_map_count.c |   41 +++++++++++++++++--------
>   1 files changed, 28 insertions(+), 13 deletions(-)
>
> diff --git a/testcases/kernel/mem/tunable/max_map_count.c b/testcases/kernel/mem/tunable/max_map_count.c
> index e948868..01fbe5e 100644
> --- a/testcases/kernel/mem/tunable/max_map_count.c
> +++ b/testcases/kernel/mem/tunable/max_map_count.c
> @@ -14,20 +14,16 @@
>    * The program trys to invoke mmap() endless until triggering MAP_FAILED,
>    * then read the process's maps file /proc/[pid]/maps, save the line number
>    * to map_count variable, and compare it with /proc/sys/vm/max_map_count,
> - * map_count should less than max_map_count.
> - * Note: There are two special vmas VDSO and VSYSCALL, which are allocated
> - * via install_special_mapping(), install_specail_mapping() allows the VMAs
> - * to be allocated and inserted without checking the sysctl_map_map_count,
> - * and each /proc/<pid>/maps has both at the end:
> - * # cat /proc/self/maps
> + * map_count should be greater than max_map_count by 1;
> + *
> + * Note: On some architectures there is a special vma VSYSCALL, which
> + * is allocated without incrementing mm->map_count variable. On these
> + * architectures each /proc/<pid>/maps has at the end:
>    * ...
>    * ...
> - * 7fff7b9ff000-7fff7ba00000 r-xp 00000000 00:00 0           [vdso]
>    * ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0   [vsyscall]
>    *
> - * so during comparing with map_count and /proc/sys/vm/max_map_count,
> - * we should except the two special vmas from map_count:
> - * map_count -= 2;
> + * so we ignore this line during /proc/[pid]/maps reading.
>    *
>    * ********************************************************************
>    * Copyright (C) 2012 Red Hat, Inc.
> @@ -121,6 +117,21 @@ void cleanup(void)
>   	TEST_CLEANUP;
>   }
>
> +/* This is a filter to exclude map entries which aren't accounted
> + * for in the vm_area_struct's map_count.
> + */
> +#if defined(__x86_64__) || defined(__x86__)
> +static int filter_map(char *buf)
> +{
> +	return strcmp(buf, "[vsyscall]") == 0;
> +}
> +#else
> +static int filter_map(char *buf)
> +{
> +	return 0;
> +}
> +#endif
> +
>   static long count_maps(pid_t pid)
>   {
>   	FILE *fp;
> @@ -136,8 +147,7 @@ static long count_maps(pid_t pid)
>   	while (getline(&line, &len, fp) != -1) {
>   		/* exclude vdso and vsyscall */
>   		if (sscanf(line, "%*p-%*p %*4s %*p %*2d:%*2d %*d %s", buf) ==
> -		    1 && ((strcmp(buf, "[vdso]") == 0) ||
> -			  (strcmp(buf, "[vsyscall]") == 0)))
> +				1 && filter_map(buf))
>   			continue;
>   		map_count++;
>   	}
> @@ -202,7 +212,12 @@ static void max_map_count_test(void)
>   			tst_brkm(TBROK, cleanup, "child did not stopped");
>
>   		map_count = count_maps(pid);
> -		if (map_count == max_maps)
> +		/* Note max_maps will be exceeded by one for
> +		 * the sysctl setting of max_map_count. This
> +		 * is the mm failure point at the time of
> +		 * writing this COMMENT!
> +		*/
> +		if (map_count == (max_maps + 1))
>   			tst_resm(TPASS, "%ld map entries in total "
>   				 "as expected.", max_maps);
>   		else
>


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