rcutorture: Make stutter_wait() caller restore priority

Currently, stutter_wait() will happily spin waiting for the stutter
interval to end even if the caller is running at a real-time priority
level.  This could starve normal-priority tasks for no good reason.  This
commit therefore drops the calling task's priority to SCHED_OTHER MAX_NICE
if stutter_wait() needs to wait.  But when it waits, stutter_wait()
returns true, which allows the caller to restore the priority if needed.
Callers that were already running at SCHED_OTHER MAX_NICE obviously
do not need any changes, but this commit also restores priority for
higher-priority callers.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

1 files changed, 4 insertions, 5 deletions

diff --git a/kernel/torture.c b/kernel/torture.c
index 56ff02bf444f..8562ac18d2eb 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -604,19 +604,19 @@ bool stutter_wait(const char *title)
 {
 	ktime_t delay;
 	unsigned int i = 0;
-	int oldnice;
 	bool ret = false;
 	int spt;
 
 	cond_resched_tasks_rcu_qs();
 	spt = READ_ONCE(stutter_pause_test);
 	for (; spt; spt = READ_ONCE(stutter_pause_test)) {
-		ret = true;
+		if (!ret) {
+			sched_set_normal(current, MAX_NICE);
+			ret = true;
+		}
 		if (spt == 1) {
 			schedule_timeout_interruptible(1);
 		} else if (spt == 2) {
-			oldnice = task_nice(current);
-			set_user_nice(current, MAX_NICE);
 			while (READ_ONCE(stutter_pause_test)) {
 				if (!(i++ & 0xffff)) {
 					set_current_state(TASK_INTERRUPTIBLE);
@@ -625,7 +625,6 @@ bool stutter_wait(const char *title)
 				}
 				cond_resched();
 			}
-			set_user_nice(current, oldnice);
 		} else {
 			schedule_timeout_interruptible(round_jiffies_relative(HZ));
 		}