rcu: Assign higher prio to RCU threads if rcutorture is built-in

The rcutorture RCU priority boosting tests fail even with CONFIG_RCU_BOOST
set because rcutorture's threads run at the same priority as 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 RT priority 1 to the RCU threads, allowing the rcutorture boost
tests to pass.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7498a416f63b32161ccbb150fc3b232915091270..8143b8d40a6cf335c79e062c2e557bbb0b8b6308 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3923,12 +3923,16 @@ 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);