rcu: Tighten up affinity and check for sysidle

If the RCU grace-period kthread invoking rcu_sysidle_check_cpu()
happens to be running on the tick_do_timer_cpu initially,
then rcu_bind_gp_kthread() won't bind it.  This kthread might
then migrate before invoking rcu_gp_fqs(), which will trigger the
WARN_ON_ONCE() in rcu_sysidle_check_cpu().  This commit therefore makes
rcu_bind_gp_kthread() do the binding even if the kthread is currently
on the same CPU.  Because this incurs added overhead, this commit also
causes each RCU grace-period kthread to invoke rcu_bind_gp_kthread()
once at boot rather than at the beginning of each grace period.
And as long as rcu_bind_gp_kthread() is being modified, this commit
eliminates its #ifdef.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 735bd7ee749a..a6972c20eaa5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1707,7 +1707,6 @@ static int rcu_gp_init(struct rcu_state *rsp)
         struct rcu_node *rnp = rcu_get_root(rsp);
 
         ACCESS_ONCE(rsp->gp_activity) = jiffies;
-        rcu_bind_gp_kthread();
         raw_spin_lock_irq(&rnp->lock);
         smp_mb__after_unlock_lock();
         if (!ACCESS_ONCE(rsp->gp_flags)) {
@@ -1895,6 +1894,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
         struct rcu_state *rsp = arg;
         struct rcu_node *rnp = rcu_get_root(rsp);
 
+        rcu_bind_gp_kthread();
         for (;;) {
 
                 /* Handle grace-period start. */