[PATCH rcu 3/9] torture: Add lock_torture_writer_fifo module param

["Paul E. McKenney" <paulmck@xxxxxxxxxx>]

From: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>

Modifies locktorture writer to run as RT task.

To use it:
insmod /lib/modules/torture.ko random_shuffle=1 lock_torture_writer_fifo=1
                                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
insmod /lib/modules/locktorture.ko torture_type=mutex_lock rt_boost=1 rt_boost_factor=50 nested_locks=3

This patch has been helpful to uncover issues with the proxy-execution
series.

Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: kernel-team@xxxxxxxxxxx
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
[jstultz: Include header change to build, reword commit message]
Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
Acked-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/locking/locktorture.c |  3 ++-
 kernel/torture.c             | 11 ++++++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 949d3deae506..aac48d323254 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -809,7 +809,8 @@ static int lock_torture_writer(void *arg)
 	bool skip_main_lock;
 
 	VERBOSE_TOROUT_STRING("lock_torture_writer task started");
-	set_user_nice(current, MAX_NICE);
+	if (!rt_task(current))
+		set_user_nice(current, MAX_NICE);
 
 	do {
 		if ((torture_random(&rand) & 0xfffff) == 0)
diff --git a/kernel/torture.c b/kernel/torture.c
index 8be83fdc6be1..db79197e257a 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -37,6 +37,7 @@
 #include <linux/ktime.h>
 #include <asm/byteorder.h>
 #include <linux/torture.h>
+#include <linux/sched/rt.h>
 #include "rcu/rcu.h"
 
 MODULE_LICENSE("GPL");
@@ -57,6 +58,9 @@ module_param(verbose_sleep_duration, int, 0444);
 static int random_shuffle;
 module_param(random_shuffle, int, 0444);
 
+static int lock_torture_writer_fifo;
+module_param(lock_torture_writer_fifo, int, 0444);
+
 static char *torture_type;
 static int verbose;
 
@@ -734,7 +738,7 @@ bool stutter_wait(const char *title)
 	cond_resched_tasks_rcu_qs();
 	spt = READ_ONCE(stutter_pause_test);
 	for (; spt; spt = READ_ONCE(stutter_pause_test)) {
-		if (!ret) {
+		if (!ret && !rt_task(current)) {
 			sched_set_normal(current, MAX_NICE);
 			ret = true;
 		}
@@ -944,6 +948,11 @@ int _torture_create_kthread(int (*fn)(void *arg), void *arg, char *s, char *m,
 		*tp = NULL;
 		return ret;
 	}
+
+	if (lock_torture_writer_fifo &&
+	    !strncmp(s, "lock_torture_writer", strlen(s)))
+		sched_set_fifo(*tp);
+
 	wake_up_process(*tp);  // Process is sleeping, so ordering provided.
 	torture_shuffle_task_register(*tp);
 	return ret;
-- 
2.40.1