[PATCH] move_task_off_dead_cpu() should be called with disabled ints

move_task_off_dead_cpu() requires interrupts to be disabled, while
migrate_dead() calls it with enabled interrupts.  Added appropriate
comments to functions and added BUG_ON(!irqs_disabled()) into
double_rq_lock() and double_lock_balance() which are the origin sources of
such bugs.

Signed-off-by: Kirill Korotaev <dev@openvz.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index a08387b5f7fa..f04add905bdf 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1952,6 +1952,7 @@ static void double_rq_lock(struct rq *rq1, struct rq *rq2)
         __acquires(rq1->lock)
         __acquires(rq2->lock)
 {
+        BUG_ON(!irqs_disabled());
         if (rq1 == rq2) {
                 spin_lock(&rq1->lock);
                 __acquire(rq2->lock);   /* Fake it out ;) */
@@ -1991,6 +1992,11 @@ static void double_lock_balance(struct rq *this_rq, struct rq *busiest)
         __acquires(busiest->lock)
         __acquires(this_rq->lock)
 {
+        if (unlikely(!irqs_disabled())) {
+                /* printk() doesn't work good under rq->lock */
+                spin_unlock(&this_rq->lock);
+                BUG_ON(1);
+        }
         if (unlikely(!spin_trylock(&busiest->lock))) {
                 if (busiest < this_rq) {
                         spin_unlock(&this_rq->lock);
@@ -5067,7 +5073,10 @@ wait_to_die:
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
-/* Figure out where task on dead CPU should go, use force if neccessary. */
+/*
+ * Figure out where task on dead CPU should go, use force if neccessary.
+ * NOTE: interrupts should be disabled by the caller
+ */
 static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)
 {
         unsigned long flags;
@@ -5187,6 +5196,7 @@ void idle_task_exit(void)
         mmdrop(mm);
 }
 
+/* called under rq->lock with disabled interrupts */
 static void migrate_dead(unsigned int dead_cpu, struct task_struct *p)
 {
         struct rq *rq = cpu_rq(dead_cpu);
@@ -5203,10 +5213,11 @@ static void migrate_dead(unsigned int dead_cpu, struct task_struct *p)
          * Drop lock around migration; if someone else moves it,
          * that's OK.  No task can be added to this CPU, so iteration is
          * fine.
+         * NOTE: interrupts should be left disabled  --dev@
          */
-        spin_unlock_irq(&rq->lock);
+        spin_unlock(&rq->lock);
         move_task_off_dead_cpu(dead_cpu, p);
-        spin_lock_irq(&rq->lock);
+        spin_lock(&rq->lock);
 
         put_task_struct(p);
 }