[PATCH] PCI: hv: Fix panic by calling hv_pci_remove_slots() earlier

[Dexuan Cui]

When a slot is removed, the pci_dev must still exist.

pci_remove_root_bus() removes and free all the pci_devs, so
hv_pci_remove_slots() must be called before pci_remove_root_bus(),
otherwise a general protection fault can happen, if the kernel is built
with the memory debugging options.

Fixes: 15becc2b56c6 ("PCI: hv: Add hv_pci_remove_slots() when we unload the driver")
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx

---

When pci-hyperv is unloaded, this panic can happen:

 general protection fault:
 CPU: 2 PID: 1091 Comm: rmmod Not tainted 5.2.0+
 RIP: 0010:pci_slot_release+0x30/0xd0
 Call Trace:
  kobject_release+0x65/0x190
  pci_destroy_slot+0x25/0x60
  hv_pci_remove+0xec/0x110 [pci_hyperv]
  vmbus_remove+0x20/0x30 [hv_vmbus]
  device_release_driver_internal+0xd5/0x1b0
  driver_detach+0x44/0x7c
  bus_remove_driver+0x75/0xc7
  vmbus_driver_unregister+0x50/0xbd [hv_vmbus]
  __x64_sys_delete_module+0x136/0x200
  do_syscall_64+0x5e/0x220

 drivers/pci/controller/pci-hyperv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 6b9cc6e60a..68c611d 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -2757,8 +2757,8 @@ static int hv_pci_remove(struct hv_device *hdev)
 		/* Remove the bus from PCI's point of view. */
 		pci_lock_rescan_remove();
 		pci_stop_root_bus(hbus->pci_bus);
-		pci_remove_root_bus(hbus->pci_bus);
 		hv_pci_remove_slots(hbus);
+		pci_remove_root_bus(hbus->pci_bus);
 		pci_unlock_rescan_remove();
 		hbus->state = hv_pcibus_removed;
 	}
-- 
1.8.3.1