rcu: Prevent RCU callbacks from executing before scheduler initialized
Under some rare but real combinations of configuration parameters, RCU
callbacks are posted during early boot that use kernel facilities that
are not yet initialized. Therefore, when these callbacks are invoked,
hard hangs and crashes ensue. This commit therefore prevents RCU
callbacks from being invoked until after the scheduler is fully up and
running, as in after multiple tasks have been spawned.
It might well turn out that a better approach is to identify the specific
RCU callbacks that are causing this problem, but that discussion will
wait until such time as someone really needs an RCU callback to be invoked
(as opposed to merely registered) during early boot.
Reported-by: julie Sullivan <kernelmail.jms@gmail.com>
Reported-by: RKK <kulkarni.ravi4@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: julie Sullivan <kernelmail.jms@gmail.com>
Tested-by: RKK <kulkarni.ravi4@gmail.com>
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 14dc7dd..75113cb 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1532,7 +1532,7 @@
struct sched_param sp;
struct task_struct *t;
- if (!rcu_kthreads_spawnable ||
+ if (!rcu_scheduler_fully_active ||
per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
return 0;
t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
@@ -1639,7 +1639,7 @@
struct sched_param sp;
struct task_struct *t;
- if (!rcu_kthreads_spawnable ||
+ if (!rcu_scheduler_fully_active ||
rnp->qsmaskinit == 0)
return 0;
if (rnp->node_kthread_task == NULL) {
@@ -1665,7 +1665,7 @@
int cpu;
struct rcu_node *rnp;
- rcu_kthreads_spawnable = 1;
+ rcu_scheduler_fully_active = 1;
for_each_possible_cpu(cpu) {
per_cpu(rcu_cpu_has_work, cpu) = 0;
if (cpu_online(cpu))
@@ -1687,7 +1687,7 @@
struct rcu_node *rnp = rdp->mynode;
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
- if (rcu_kthreads_spawnable) {
+ if (rcu_scheduler_fully_active) {
(void)rcu_spawn_one_cpu_kthread(cpu);
if (rnp->node_kthread_task == NULL)
(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
@@ -1726,6 +1726,13 @@
{
}
+static int __init rcu_scheduler_really_started(void)
+{
+ rcu_scheduler_fully_active = 1;
+ return 0;
+}
+early_initcall(rcu_scheduler_really_started);
+
static void __cpuinit rcu_prepare_kthreads(int cpu)
{
}