From ef46a13b9c4e49db8aeb319ced36f2c6d34e6bad Mon Sep 17 00:00:00 2001
From: Peter Xu <peterx@redhat.com>
Date: Wed, 15 Mar 2017 16:01:17 +0800
Subject: KVM: x86: clear bus pointer when destroyed
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commit df630b8c1e851b5e265dc2ca9c87222e342c093b upstream.

When releasing the bus, let's clear the bus pointers to mark it out. If
any further device unregister happens on this bus, we know that we're
done if we found the bus being released already.

Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 7f9ee29..edc7591 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -720,8 +720,10 @@ static void kvm_destroy_vm(struct kvm *kvm)
 	list_del(&kvm->vm_list);
 	spin_unlock(&kvm_lock);
 	kvm_free_irq_routing(kvm);
-	for (i = 0; i < KVM_NR_BUSES; i++)
+	for (i = 0; i < KVM_NR_BUSES; i++) {
 		kvm_io_bus_destroy(kvm->buses[i]);
+		kvm->buses[i] = NULL;
+	}
 	kvm_coalesced_mmio_free(kvm);
 #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
 	mmu_notifier_unregister(&kvm->mmu_notifier, kvm->mm);
@@ -3568,6 +3570,14 @@ int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
 	struct kvm_io_bus *new_bus, *bus;
 
 	bus = kvm->buses[bus_idx];
+
+	/*
+	 * It's possible the bus being released before hand. If so,
+	 * we're done here.
+	 */
+	if (!bus)
+		return 0;
+
 	r = -ENOENT;
 	for (i = 0; i < bus->dev_count; i++)
 		if (bus->range[i].dev == dev) {
-- 
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