linux-kernel - [04/39] clockevents: Prevent clockevent_devices list corruption on cpu hotplug

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Date:	Tue, 05 Jan 2010 12:02:00 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	stable-review@...nel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>
Subject: [04/39] clockevents: Prevent clockevent_devices list corruption on cpu hotplug

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

------------------

From: Thomas Gleixner <tglx@...utronix.de>

commit bb6eddf7676e1c1f3e637aa93c5224488d99036f upstream.

Xiaotian Feng triggered a list corruption in the clock events list on
CPU hotplug and debugged the root cause.

If a CPU registers more than one per cpu clock event device, then only
the active clock event device is removed on CPU_DEAD. The unused
devices are kept in the clock events device list.

On CPU up the clock event devices are registered again, which means
that we list_add an already enqueued list_head. That results in list
corruption.

Resolve this by removing all devices which are associated to the dead
CPU on CPU_DEAD.

Reported-by: Xiaotian Feng <dfeng@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Xiaotian Feng <dfeng@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/time/clockevents.c |   18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -237,8 +237,9 @@ void clockevents_exchange_device(struct 
  */
 void clockevents_notify(unsigned long reason, void *arg)
 {
-	struct list_head *node, *tmp;
+	struct clock_event_device *dev, *tmp;
 	unsigned long flags;
+	int cpu;
 
 	spin_lock_irqsave(&clockevents_lock, flags);
 	clockevents_do_notify(reason, arg);
@@ -249,8 +250,19 @@ void clockevents_notify(unsigned long re
 		 * Unregister the clock event devices which were
 		 * released from the users in the notify chain.
 		 */
-		list_for_each_safe(node, tmp, &clockevents_released)
-			list_del(node);
+		list_for_each_entry_safe(dev, tmp, &clockevents_released, list)
+			list_del(&dev->list);
+		/*
+		 * Now check whether the CPU has left unused per cpu devices
+		 */
+		cpu = *((int *)arg);
+		list_for_each_entry_safe(dev, tmp, &clockevent_devices, list) {
+			if (cpumask_test_cpu(cpu, dev->cpumask) &&
+			    cpumask_weight(dev->cpumask) == 1) {
+				BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
+				list_del(&dev->list);
+			}
+		}
 		break;
 	default:
 		break;


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