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>

2 files changed, 7 insertions, 7 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. */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 0a571e9a0f1d..b46c92824db1 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2763,7 +2763,8 @@ static void rcu_sysidle_exit(int irq)
 
 /*
  * Check to see if the current CPU is idle.  Note that usermode execution
- * does not count as idle.  The caller must have disabled interrupts.
+ * does not count as idle.  The caller must have disabled interrupts,
+ * and must be running on tick_do_timer_cpu.
  */
 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
                                   unsigned long *maxj)
@@ -2784,8 +2785,8 @@ static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
         if (!*isidle || rdp->rsp != rcu_state_p ||
             cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
                 return;
-        if (rcu_gp_in_progress(rdp->rsp))
-                WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
+        /* Verify affinity of current kthread. */
+        WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
 
         /* Pick up current idle and NMI-nesting counter and check. */
         cur = atomic_read(&rdtp->dynticks_idle);
@@ -3068,11 +3069,10 @@ static void rcu_bind_gp_kthread(void)
                 return;
 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
         cpu = tick_do_timer_cpu;
-        if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
+        if (cpu >= 0 && cpu < nr_cpu_ids)
                 set_cpus_allowed_ptr(current, cpumask_of(cpu));
 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
-        if (!is_housekeeping_cpu(raw_smp_processor_id()))
-                housekeeping_affine(current);
+        housekeeping_affine(current);
 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
 }