rcu: Prevent RCU callbacks from executing before scheduler initialized

This is a port of commit #b0d3041 from TREE_RCU to TREE_PREEMPT_RCU.

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.

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

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 51bf29c8148560de2ad23671c92cce151e80c1b7..e93df77176d163fdb8a810a3029264a4e49d57cb 100644 (file)
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -27,13 +27,9 @@
 
 #include <linux/cache.h>
 
-#ifdef CONFIG_RCU_BOOST
 static inline void rcu_init(void)
 {
 }
-#else /* #ifdef CONFIG_RCU_BOOST */
-void rcu_init(void);
-#endif /* #else #ifdef CONFIG_RCU_BOOST */
 
 static inline void rcu_barrier_bh(void)
 {

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index b58a3200f0ff0948b48329aeb7c999d4523abac8..95df60ebe363ec6cd2f3390e4474eff52e12e00d 100644 (file)
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -914,7 +914,8 @@ static void rcu_preempt_process_callbacks(void)
 static void invoke_rcu_callbacks(void)
 {
        have_rcu_kthread_work = 1;
-       wake_up(&rcu_kthread_wq);
+       if (rcu_kthread_task != NULL)
+               wake_up(&rcu_kthread_wq);
 }
 
 #ifdef CONFIG_RCU_TRACE
@@ -975,12 +976,16 @@ early_initcall(rcu_spawn_kthreads);
 
 #else /* #ifdef CONFIG_RCU_BOOST */
 
+/* Hold off callback invocation until early_initcall() time. */
+static int rcu_scheduler_fully_active __read_mostly;
+
 /*
  * Start up softirq processing of callbacks.
  */
 void invoke_rcu_callbacks(void)
 {
-       raise_softirq(RCU_SOFTIRQ);
+       if (rcu_scheduler_fully_active)
+               raise_softirq(RCU_SOFTIRQ);
 }
 
 #ifdef CONFIG_RCU_TRACE
@@ -995,10 +1000,14 @@ static bool rcu_is_callbacks_kthread(void)
 
 #endif /* #ifdef CONFIG_RCU_TRACE */
 
-void rcu_init(void)
+static int __init rcu_scheduler_really_started(void)
 {
+       rcu_scheduler_fully_active = 1;
        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+       raise_softirq(RCU_SOFTIRQ);  /* Invoke any callbacks from early boot. */
+       return 0;
 }
+early_initcall(rcu_scheduler_really_started);
 
 #endif /* #else #ifdef CONFIG_RCU_BOOST */