Fix PREEMPT_RCU without HOTPLUG_CPU

70ff0555 · Nick Piggin <[email protected]> · 2008-07-10 17:25:35 +10:00

PREEMPT_RCU without HOTPLUG_CPU is broken.  The rcu_online_cpu is called
to initially populate rcu_cpu_online_map with all online CPUs when the
hotplug event handler is installed, and also to populate the map with
CPUs as they come online.  The former case is meant to happen with and
without HOTPLUG_CPU, but without HOTPLUG_CPU, the rcu_offline_cpu
function is no-oped -- while it still gets called, it does not set the
rcu CPU map.

With a blank RCU CPU map, grace periods get to tick by completely
oblivious to active RCU read side critical sections.  This results in
free-before-grace bugs.

Fix is obvious once the problem is known. (Also, change __devinit to
__cpuinit so the function gets thrown away on !HOTPLUG_CPU kernels).

Signed-off-by: Nick Piggin <[email protected]>
Reported-and-tested-by: Alexey Dobriyan <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Cc: Paul E. McKenney <[email protected]>
[ Nick is my personal hero of the day - Linus ]
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 70ff05554f91a1edda1f11684da1dbde09e2feea
Parents: eb6d42ea

Changes

1 files changed · +8 −12

File	Status	Add	Del	Content
kernel/rcupreempt.c	modified	+8	−12	View file

kernel/rcupreempt.c

View file

diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
index 5e02b77..41d275a 100644
--- a/kernel/rcupreempt.c
+++ b/kernel/rcupreempt.c
@@ -925,26 +925,22 @@ void rcu_offline_cpu(int cpu)
 	spin_unlock_irqrestore(&rdp->lock, flags);
 }
 
-void __devinit rcu_online_cpu(int cpu)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
-	cpu_set(cpu, rcu_cpu_online_map);
-	spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
-}
-
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
 
 void rcu_offline_cpu(int cpu)
 {
 }
 
-void __devinit rcu_online_cpu(int cpu)
+#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
+
+void __cpuinit rcu_online_cpu(int cpu)
 {
-}
+	unsigned long flags;
 
-#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
+	spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
+	cpu_set(cpu, rcu_cpu_online_map);
+	spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
+}
 
 static void rcu_process_callbacks(struct softirq_action *unused)
 {