virtio-mem: only mark the device ready in kdump mode with vmcore support

virtio_mem_init_kdump() marks the device DRIVER_OK before it checks for CONFIG_PROC_VMCORE. Without vmcore support it then fails with -EBUSY, and virtio_mem_probe() deletes the virtqueue on that error path without resetting the device first. The device is left with DRIVER_OK set and a queue that points at freed memory. Nothing has been queued at that point, so the device has nothing to process, but the driver should not leave a device it is giving up on marked ready.

Before commit a9403425b3cf ("virtio-mem: mark device ready before registering callbacks in kdump mode"), virtio_mem_probe() called virtio_device_ready() only after virtio_mem_init() had succeeded, so this path never exposed a ready device.

Move virtio_device_ready() into the CONFIG_PROC_VMCORE branch, right before the vmcore callbacks that need it are registered, so the -EBUSY path never sets DRIVER_OK.

---
v2:
- Drop Cc: stable, as no practical kdump kernel disables PROC_VMCORE (David).
- Say in the changelog that nothing is queued on this path.
- Rebased on v7.4-rc1.

v1: https://lore.kernel.org/r/[email protected]

Compile-tested with W=1, with and without CONFIG_PROC_VMCORE.

 drivers/virtio/virtio_mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index e18dd736f2ec..b28d2da7d5b6 100644
@@ -2817,9 +2817,9 @@ static int virtio_mem_vmcore_get_device_ram(struct vmcore_cb *cb,
 
 static int virtio_mem_init_kdump(struct virtio_mem *vm)
 {
+#ifdef CONFIG_PROC_VMCORE
 	/* We must be prepared to receive a callback immediately. */
 	virtio_device_ready(vm->vdev);
-#ifdef CONFIG_PROC_VMCORE
 	dev_info(&vm->vdev->dev, "memory hot(un)plug disabled in kdump kernel\n");
 	vm->vmcore_cb.pfn_is_ram = virtio_mem_vmcore_pfn_is_ram;
 #ifdef CONFIG_PROC_VMCORE_DEVICE_RAM

2.43.0