[PATCH v2] vmd: Fix infinite loop executing irq's

[Keith Busch <keith.busch@xxxxxxxxx>]

We can't initialize the list head on deletion as this causes the node
to point to itself, looping infinitely if the vmd IRQ handler happened
to be servicing that node.

The list initialization was trying fix a bug from multiple calls to
disable the same IRQ. We can fix this instead by having the vmd driver
track if the interrupt is enabled.

Signed-off-by: Keith Busch <keith.busch@xxxxxxxxx>
Cc: Jon Derrick <jonathan.derrick@xxxxxxxxx>
Reported-by: Grzegorz Koczot <grzegorz.koczot@xxxxxxxxx>
Tested-by: Miroslaw Drost <miroslaw.drost@xxxxxxxxx>
---
v1 -> v2:

  Removed check for poisioned list pointer. This is abusing knowledge
  internal to the list api, so we need another way to know if the child
  irq is enabled. This patch uses a driver controlled boolean for this.

  Added tags for the bug reporter and tester.

 arch/x86/pci/vmd.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/pci/vmd.c b/arch/x86/pci/vmd.c
index e88b417..4b85837 100644
--- a/arch/x86/pci/vmd.c
+++ b/arch/x86/pci/vmd.c
@@ -41,6 +41,7 @@ static DEFINE_RAW_SPINLOCK(list_lock);
  * @node:	list item for parent traversal.
  * @rcu:	RCU callback item for freeing.
  * @irq:	back pointer to parent.
+ * @enabled:	true if driver enabled irq
  * @virq:	the virtual IRQ value provided to the requesting driver.
  *
  * Every MSI/MSI-X IRQ requested for a device in a VMD domain will be mapped to
@@ -50,6 +51,7 @@ struct vmd_irq {
 	struct list_head	node;
 	struct rcu_head		rcu;
 	struct vmd_irq_list	*irq;
+	bool			enabled;
 	unsigned int		virq;
 };
 
@@ -122,7 +124,9 @@ static void vmd_irq_enable(struct irq_data *data)
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&list_lock, flags);
+	WARN_ON(vmdirq->enabled);
 	list_add_tail_rcu(&vmdirq->node, &vmdirq->irq->irq_list);
+	vmdirq->enabled = true;
 	raw_spin_unlock_irqrestore(&list_lock, flags);
 
 	data->chip->irq_unmask(data);
@@ -136,8 +140,10 @@ static void vmd_irq_disable(struct irq_data *data)
 	data->chip->irq_mask(data);
 
 	raw_spin_lock_irqsave(&list_lock, flags);
-	list_del_rcu(&vmdirq->node);
-	INIT_LIST_HEAD_RCU(&vmdirq->node);
+	if (vmdirq->enabled) {
+		list_del_rcu(&vmdirq->node);
+		vmdirq->enabled = false;
+	}
 	raw_spin_unlock_irqrestore(&list_lock, flags);
 }
 
-- 
2.7.2

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