Right now the following sequence of events can happen:
1. Thread X calls vgic_put_irq
2. Thread Y calls vgic_add_lpi
3. Thread Y gets lpi_list_lock
4. Thread X drops the ref count to 0 and blocks on lpi_list_lock
5. Thread Y finds the irq via the lpi_list_lock, raises the ref
count to 1, and release the lpi_list_lock.
6. Thread X proceeds and frees the irq.
Avoid this by holding the spinlock around the kref_put.
Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
---
Notes:
Changes since v1:
- Stylistic change: Don't use else branch
virt/kvm/arm/vgic/vgic.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
index e7aeac7..e83b7fe 100644
--- a/virt/kvm/arm/vgic/vgic.c
+++ b/virt/kvm/arm/vgic/vgic.c
@@ -117,17 +117,17 @@ static void vgic_irq_release(struct kref *ref)
void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
{
- struct vgic_dist *dist;
+ struct vgic_dist *dist = &kvm->arch.vgic;
if (irq->intid < VGIC_MIN_LPI)
return;
- if (!kref_put(&irq->refcount, vgic_irq_release))
+ spin_lock(&dist->lpi_list_lock);
+ if (!kref_put(&irq->refcount, vgic_irq_release)) {
+ spin_unlock(&dist->lpi_list_lock);
return;
+ };
- dist = &kvm->arch.vgic;
-
- spin_lock(&dist->lpi_list_lock);
list_del(&irq->lpi_list);
dist->lpi_list_count--;
spin_unlock(&dist->lpi_list_lock);
--
2.9.0
--
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