[PATCH v2 1/3] rcu: Assign higher prio to RCU threads if rcutorture is built-in

[Joel Fernandes]

From: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>

rcutorture boost tests fail even with CONFIG_RCU_BOOST set because
rcutorture's threads are equal priority to the default RCU kthreads (RT
class with priority of 1).

This patch checks if RCU torture is built into the kernel and if so,
assigns a higher priority to the RCU threads. With this the rcutorture
boost tests pass.

Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
---
 kernel/rcu/tree.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index deb2508be923..92c29439eba6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3884,12 +3884,16 @@ static int __init rcu_spawn_gp_kthread(void)
 	struct task_struct *t;
 
 	/* Force priority into range. */
-	if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
+	if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
+	    && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
+		kthread_prio = 2;
+	else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
 		kthread_prio = 1;
 	else if (kthread_prio < 0)
 		kthread_prio = 0;
 	else if (kthread_prio > 99)
 		kthread_prio = 99;
+
 	if (kthread_prio != kthread_prio_in)
 		pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
 			 kthread_prio, kthread_prio_in);
-- 
2.18.0.rc1.244.gcf134e6275-goog