[patch 143/262] userfaultfd/selftests: don't rely on GNU extensions for random numbers

Andrew Morton
2021-11-05T20:42:10Z

From: Axel Rasmussen <axelrasmussen@google.com>
Subject: userfaultfd/selftests: don't rely on GNU extensions for random numbers

Patch series "Small userfaultfd selftest fixups", v2.

This patch (of 3):

Two arguments for doing this:

First, and maybe most importantly, the resulting code is significantly
shorter / simpler.

Then, we avoid using GNU libc extensions. Why does this matter? It makes
testing userfaultfd with the selftest easier e.g. on distros which use
something other than glibc (e.g., Alpine, which uses musl); basically, it
makes the test more portable.

Link: https://lkml.kernel.org/r/20210930212309.4001967-2-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

tools/testing/selftests/vm/userfaultfd.c | 26 +++------------------
1 file changed, 4 insertions(+), 22 deletions(-)

--- a/tools/testing/selftests/vm/userfaultfd.c~userfaultfd-selftests-dont-rely-on-gnu-extensions-for-random-numbers
+++ a/tools/testing/selftests/vm/userfaultfd.c
@@ -57,6 +57,7 @@
#include <assert.h>
#include <inttypes.h>
#include <stdint.h>
+#include <sys/random.h>

#include "../kselftest.h"

@@ -518,22 +519,10 @@ static void continue_range(int ufd, __u6
static void *locking_thread(void *arg)
{
unsigned long cpu = (unsigned long) arg;
- struct random_data rand;
unsigned long page_nr = *(&(page_nr)); /* uninitialized warning */
- int32_t rand_nr;
unsigned long long count;
- char randstate[64];
- unsigned int seed;

- if (bounces & BOUNCE_RANDOM) {
- seed = (unsigned int) time(NULL) - bounces;
- if (!(bounces & BOUNCE_RACINGFAULTS))
- seed += cpu;
- bzero(&rand, sizeof(rand));
- bzero(&randstate, sizeof(randstate));
- if (initstate_r(seed, randstate, sizeof(randstate), &rand))
- err("initstate_r failed");
- } else {
+ if (!(bounces & BOUNCE_RANDOM)) {
page_nr = -bounces;
if (!(bounces & BOUNCE_RACINGFAULTS))
page_nr += cpu * nr_pages_per_cpu;
@@ -541,15 +530,8 @@ static void *locking_thread(void *arg)

while (!finished) {
if (bounces & BOUNCE_RANDOM) {
- if (random_r(&rand, &rand_nr))
- err("random_r failed");
- page_nr = rand_nr;
- if (sizeof(page_nr) > sizeof(rand_nr)) {
- if (random_r(&rand, &rand_nr))
- err("random_r failed");
- page_nr |= (((unsigned long) rand_nr) << 16) <<
- 16;
- }
+ if (getrandom(&page_nr, sizeof(page_nr), 0) != sizeof(page_nr))
+ err("getrandom failed");
} else
page_nr += 1;
page_nr %= nr_pages;
_