selftests/mm: don't fail uffd-stress if too many CPUs

This calculation divides a fixed parameter by an environment-dependent
parameter i.e.  the number of CPUs.

The simple way to avoid machine-specific failures here is to just put a
cap on the max value of the latter.

Link: https://lkml.kernel.org/r/20250311-mm-selftests-v4-6-dec210a658f5@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Suggested-by: Mateusz Guzik <mjguzik@gmail.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
index 4ba5bf13a0108435ce8b53340b9e17ccd47e859e..40af7f67c4074d901be6608e5d64bd0490026dae 100644 (file)
--- a/tools/testing/selftests/mm/uffd-stress.c
+++ b/tools/testing/selftests/mm/uffd-stress.c
@@ -435,6 +435,7 @@ static void sigalrm(int sig)
 
 int main(int argc, char **argv)
 {
+       unsigned long nr_cpus;
        size_t bytes;
 
        if (argc < 4)
@@ -453,7 +454,15 @@ int main(int argc, char **argv)
                return KSFT_SKIP;
        }
 
-       nr_parallel = sysconf(_SC_NPROCESSORS_ONLN);
+       nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+       if (nr_cpus > 32) {
+               /* Don't let calculation below go to zero. */
+               ksft_print_msg("_SC_NPROCESSORS_ONLN (%lu) too large, capping nr_threads to 32\n",
+                              nr_cpus);
+               nr_parallel = 32;
+       } else {
+               nr_parallel = nr_cpus;
+       }
 
        nr_pages_per_cpu = bytes / page_size / nr_parallel;
        if (!nr_pages_per_cpu) {