Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU fix from Paul E. McKenney:

 "This additional v4.18 pull request contains a single commit that fell
  through the cracks:

      Provide early rcu_cpu_starting() callback for the benefit of the
      x86/mtrr code, which needs RCU to be available on incoming CPUs
      earlier than has been the case in the past."

Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/mtrr/main.c

@@ -46,6 +46,7 @@
 #include <linux/pci.h>
 #include <linux/smp.h>
 #include <linux/syscore_ops.h>
+#include <linux/rcupdate.h>
 
 #include <asm/cpufeature.h>
 #include <asm/e820/api.h>
@@ -793,6 +794,9 @@ void mtrr_ap_init(void)
 
 	if (!use_intel() || mtrr_aps_delayed_init)
 		return;
+
+	rcu_cpu_starting(smp_processor_id());
+
 	/*
 	 * Ideally we should hold mtrr_mutex here to avoid mtrr entries
 	 * changed, but this routine will be called in cpu boot time,

include/linux/rcupdate.h

@@ -108,7 +108,6 @@ void rcu_sched_qs(void);
 void rcu_bh_qs(void);
 void rcu_check_callbacks(int user);
 void rcu_report_dead(unsigned int cpu);
-void rcu_cpu_starting(unsigned int cpu);
 void rcutree_migrate_callbacks(int cpu);
 
 #ifdef CONFIG_RCU_STALL_COMMON

include/linux/rcutiny.h

@@ -132,5 +132,6 @@ static inline void rcu_all_qs(void) { barrier(); }
 #define rcutree_offline_cpu      NULL
 #define rcutree_dead_cpu         NULL
 #define rcutree_dying_cpu        NULL
+static inline void rcu_cpu_starting(unsigned int cpu) { }
 
 #endif /* __LINUX_RCUTINY_H */

include/linux/rcutree.h

@@ -101,5 +101,6 @@ int rcutree_online_cpu(unsigned int cpu);
 int rcutree_offline_cpu(unsigned int cpu);
 int rcutree_dead_cpu(unsigned int cpu);
 int rcutree_dying_cpu(unsigned int cpu);
+void rcu_cpu_starting(unsigned int cpu);
 
 #endif /* __LINUX_RCUTREE_H */

kernel/rcu/tree.c

@@ -3665,6 +3665,8 @@ int rcutree_dead_cpu(unsigned int cpu)
 	return 0;
 }
 
+static DEFINE_PER_CPU(int, rcu_cpu_started);
+
 /*
  * Mark the specified CPU as being online so that subsequent grace periods
  * (both expedited and normal) will wait on it.  Note that this means that
@@ -3686,6 +3688,11 @@ void rcu_cpu_starting(unsigned int cpu)
 	struct rcu_node *rnp;
 	struct rcu_state *rsp;
 
+	if (per_cpu(rcu_cpu_started, cpu))
+		return;
+
+	per_cpu(rcu_cpu_started, cpu) = 1;
+
 	for_each_rcu_flavor(rsp) {
 		rdp = per_cpu_ptr(rsp->rda, cpu);
 		rnp = rdp->mynode;
@@ -3742,6 +3749,8 @@ void rcu_report_dead(unsigned int cpu)
 	preempt_enable();
 	for_each_rcu_flavor(rsp)
 		rcu_cleanup_dying_idle_cpu(cpu, rsp);
+
+	per_cpu(rcu_cpu_started, cpu) = 0;
 }
 
 /* Migrate the dead CPU's callbacks to the current CPU. */