rcu/x86: Provide early rcu_cpu_starting() callback

The x86/mtrr code does horrific things because hardware. It uses
stop_machine_from_inactive_cpu(), which does a wakeup (of the stopper
thread on another CPU), which uses RCU, all before the CPU is onlined.

RCU complains about this, because wakeups use RCU and RCU does
(rightfully) not consider offline CPUs for grace-periods.

Fix this by initializing RCU way early in the MTRR case.

Tested-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Add !SMP support, per 0day Test Robot report. ]

1 files changed, 9 insertions, 0 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 4fccdfa25716..aa7cade1b9f3 100644
--- a/kernel/rcu/tree.c
+++ b/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. */