[patch 58/59] move_task_off_dead_cpu() should be called with disabled ints

Chris Wright
2007-02-03T02:46:49Z

[-- Attachment #1: move_task_off_dead_cpu-should-be-called-with-disabled-ints.patch --]
[-- Type: text/plain, Size: 2474 bytes --]

-stable review patch. If anyone has any objections, please let us know.
------------------

From: Kirill Korotaev <dev@openvz.org>

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>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
kernel/sched.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

--- linux-2.6.19.2.orig/kernel/sched.c
+++ linux-2.6.19.2/kernel/sched.c
@@ -1941,6 +1941,7 @@ static void double_rq_lock(struct rq *rq
__acquires(rq1->lock)
__acquires(rq2->lock)
{
+ BUG_ON(!irqs_disabled());
if (rq1 == rq2) {
spin_lock(&rq1->lock);
__acquire(rq2->lock); /* Fake it out ;) */
@@ -1980,6 +1981,11 @@ static void double_lock_balance(struct r
__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);
@@ -5050,7 +5056,10 @@ 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;
@@ -5170,6 +5179,7 @@ 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);
@@ -5186,10 +5196,11 @@ static void migrate_dead(unsigned int de
* 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);
}

--