[RFC PATCH 10/11] torture: support randomized shuffling for proxy exec testing

["Connor O'Brien" <connoro@google.com>]

Quick hack to better surface bugs in proxy execution.

Shuffling sets the same cpu affinities for all tasks, which makes us
less likely to hit paths involving migrating blocked tasks onto a cpu
where they can't run. Add an element of randomness to allow affinities
of different writer tasks to diverge.

Signed-off-by: Connor O'Brien <connoro@google.com>
---
 kernel/torture.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/torture.c b/kernel/torture.c
index 789aeb0e1159..1d0dd88369e3 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -54,6 +54,9 @@ module_param(verbose_sleep_frequency, int, 0444);
 static int verbose_sleep_duration = 1;
 module_param(verbose_sleep_duration, int, 0444);
 
+static int random_shuffle;
+module_param(random_shuffle, int, 0444);
+
 static char *torture_type;
 static int verbose;
 
@@ -518,6 +521,7 @@ static void torture_shuffle_task_unregister_all(void)
  */
 static void torture_shuffle_tasks(void)
 {
+	DEFINE_TORTURE_RANDOM(rand);
 	struct shuffle_task *stp;
 
 	cpumask_setall(shuffle_tmp_mask);
@@ -537,8 +541,10 @@ static void torture_shuffle_tasks(void)
 		cpumask_clear_cpu(shuffle_idle_cpu, shuffle_tmp_mask);
 
 	mutex_lock(&shuffle_task_mutex);
-	list_for_each_entry(stp, &shuffle_task_list, st_l)
-		set_cpus_allowed_ptr(stp->st_t, shuffle_tmp_mask);
+	list_for_each_entry(stp, &shuffle_task_list, st_l) {
+		if (!random_shuffle || torture_random(&rand) & 0x1)
+			set_cpus_allowed_ptr(stp->st_t, shuffle_tmp_mask);
+	}
 	mutex_unlock(&shuffle_task_mutex);
 
 	cpus_read_unlock();
-- 
2.38.0.rc1.362.ged0d419d3c-goog