[PATCH v2 1/2] virtio-pci: add check for vdev in virtio_pci_isr_read

[Yuri Benditovich]

https://bugzilla.redhat.com/show_bug.cgi?id=1743098
This commit completes the solution of segfault in hot unplug flow
(by commit ccec7e9603f446fe75c6c563ba335c00cfda6a06).
Added missing check for vdev in virtio_pci_isr_read.
Typical stack of crash:
virtio_pci_isr_read ../hw/virtio/virtio-pci.c:1365 with proxy-vdev = 0
memory_region_read_accessor at ../softmmu/memory.c:442
access_with_adjusted_size at ../softmmu/memory.c:552
memory_region_dispatch_read1 at ../softmmu/memory.c:1420
memory_region_dispatch_read  at ../softmmu/memory.c:1449
flatview_read_continue at ../softmmu/physmem.c:2822
flatview_read at ../softmmu/physmem.c:2862
address_space_read_full at ../softmmu/physmem.c:2875

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
---
 hw/virtio/virtio-pci.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 883045a223..4a3dcee771 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1364,9 +1364,14 @@ static uint64_t virtio_pci_isr_read(void *opaque, hwaddr 
addr,
 {
     VirtIOPCIProxy *proxy = opaque;
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
-    uint64_t val = qatomic_xchg(&vdev->isr, 0);
-    pci_irq_deassert(&proxy->pci_dev);
+    uint64_t val;
+
+    if (vdev == NULL) {
+        return 0;
+    }
 
+    val = qatomic_xchg(&vdev->isr, 0);
+    pci_irq_deassert(&proxy->pci_dev);
     return val;
 }
 
-- 
2.17.1