path: root/virt/kvm/kvm_main.c
diff options
authorSheng Yang <>2009-01-06 10:03:03 +0800
committerAvi Kivity <>2009-02-15 02:47:36 +0200
commitba4cef31d5a397b64ba6d3ff713ce06c62f0c597 (patch)
tree50a0c4cbcad5d543dd9572c5911cc288b88c3c56 /virt/kvm/kvm_main.c
parentad8ba2cd44d4d39fb3fe55d5dcc565b19fc3a7fb (diff)
KVM: Fix racy in kvm_free_assigned_irq
In the past, kvm_get_kvm() and kvm_put_kvm() was called in assigned device irq handler and interrupt_work, in order to prevent cancel_work_sync() in kvm_free_assigned_irq got a illegal state when waiting for interrupt_work done. But it's tricky and still got two problems: 1. A bug ignored two conditions that cancel_work_sync() would return true result in a additional kvm_put_kvm(). 2. If interrupt type is MSI, we would got a window between cancel_work_sync() and free_irq(), which interrupt would be injected again... This patch discard the reference count used for irq handler and interrupt_work, and ensure the legal state by moving the free function at the very beginning of kvm_destroy_vm(). And the patch fix the second bug by disable irq before cancel_work_sync(), which may result in nested disable of irq but OK for we are going to free it. Signed-off-by: Sheng Yang <> Signed-off-by: Avi Kivity <>
Diffstat (limited to 'virt/kvm/kvm_main.c')
1 files changed, 19 insertions, 8 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 68e3f1ec1674..277ea7f39fc8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -173,7 +173,6 @@ static void kvm_assigned_dev_interrupt_work_handler(struct work_struct *work)
assigned_dev->host_irq_disabled = false;
- kvm_put_kvm(assigned_dev->kvm);
static irqreturn_t kvm_assigned_dev_intr(int irq, void *dev_id)
@@ -181,8 +180,6 @@ static irqreturn_t kvm_assigned_dev_intr(int irq, void *dev_id)
struct kvm_assigned_dev_kernel *assigned_dev =
(struct kvm_assigned_dev_kernel *) dev_id;
- kvm_get_kvm(assigned_dev->kvm);
@@ -213,6 +210,7 @@ static void kvm_assigned_dev_ack_irq(struct kvm_irq_ack_notifier *kian)
+/* The function implicit hold kvm->lock mutex due to cancel_work_sync() */
static void kvm_free_assigned_irq(struct kvm *kvm,
struct kvm_assigned_dev_kernel *assigned_dev)
@@ -228,11 +226,24 @@ static void kvm_free_assigned_irq(struct kvm *kvm,
if (!assigned_dev->irq_requested_type)
- if (cancel_work_sync(&assigned_dev->interrupt_work))
- /* We had pending work. That means we will have to take
- * care of kvm_put_kvm.
- */
- kvm_put_kvm(kvm);
+ /*
+ * In kvm_free_device_irq, cancel_work_sync return true if:
+ * 1. work is scheduled, and then cancelled.
+ * 2. work callback is executed.
+ *
+ * The first one ensured that the irq is disabled and no more events
+ * would happen. But for the second one, the irq may be enabled (e.g.
+ * for MSI). So we disable irq here to prevent further events.
+ *
+ * Notice this maybe result in nested disable if the interrupt type is
+ * INTx, but it's OK for we are going to free it.
+ *
+ * If this function is a part of VM destroy, please ensure that till
+ * now, the kvm state is still legal for probably we also have to wait
+ * interrupt_work done.
+ */
+ disable_irq_nosync(assigned_dev->host_irq);
+ cancel_work_sync(&assigned_dev->interrupt_work);
free_irq(assigned_dev->host_irq, (void *)assigned_dev);