[PATCH v2] usb:xhci fix panic in xhci_free_virt_devices_depth_first

[Yu Chen]

From: Yu Chen <chenyu56@xxxxxxxxxx>

Check vdev->real_port 0 to avoid panic
[    9.261347] [<ffffff800884a390>] xhci_free_virt_devices_depth_first+0x58/0x108
[    9.261352] [<ffffff800884a814>] xhci_mem_cleanup+0x1bc/0x570
[    9.261355] [<ffffff8008842de8>] xhci_stop+0x140/0x1c8
[    9.261365] [<ffffff80087ed304>] usb_remove_hcd+0xfc/0x1d0
[    9.261369] [<ffffff80088551c4>] xhci_plat_remove+0x6c/0xa8
[    9.261377] [<ffffff80086e928c>] platform_drv_remove+0x2c/0x70
[    9.261384] [<ffffff80086e6ea0>] __device_release_driver+0x80/0x108
[    9.261387] [<ffffff80086e7a1c>] device_release_driver+0x2c/0x40
[    9.261392] [<ffffff80086e5f28>] bus_remove_device+0xe0/0x120
[    9.261396] [<ffffff80086e2e34>] device_del+0x114/0x210
[    9.261399] [<ffffff80086e9e00>] platform_device_del+0x30/0xa0
[    9.261403] [<ffffff8008810bdc>] dwc3_otg_work+0x204/0x488
[    9.261407] [<ffffff80088133fc>] event_work+0x304/0x5b8
[    9.261414] [<ffffff80080e31b0>] process_one_work+0x148/0x490
[    9.261417] [<ffffff80080e3548>] worker_thread+0x50/0x4a0
[    9.261421] [<ffffff80080e9ea0>] kthread+0xe8/0x100
[    9.261427] [<ffffff8008083680>] ret_from_fork+0x10/0x50

The problem can occur if xhci_plat_remove() is called shortly after
xhci_plat_probe(). While xhci_free_virt_devices_depth_first been
called before the device has been setup and get real_port initialized.
The problem occurred on Hikey960 and was reproduced by Guenter Roeck
on Kevin with chromeos-4.4.

Cc: Guenter Roeck <groeck@xxxxxxxxxx>
Signed-off-by: Fan Ning <fanning4@xxxxxxxxxxxxx>
Signed-off-by: Li Rui <lirui39@xxxxxxxxxxxxx>
Signed-off-by: yangdi <yangdi10@xxxxxxxxxxxxx>
Signed-off-by: Yu Chen <chenyu56@xxxxxxxxxx>

---
 drivers/usb/host/xhci-mem.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 2a82c927ded2..0361b4a58f59 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -947,6 +947,9 @@ void xhci_free_virt_devices_depth_first(struct xhci_hcd *xhci, int slot_id)
 	if (!vdev)
 		return;
 
+	if (WARN_ON(!vdev->real_port))
+		goto out;
+
 	tt_list_head = &(xhci->rh_bw[vdev->real_port - 1].tts);
 	list_for_each_entry_safe(tt_info, next, tt_list_head, tt_list) {
 		/* is this a hub device that added a tt_info to the tts list */
@@ -960,6 +963,7 @@ void xhci_free_virt_devices_depth_first(struct xhci_hcd *xhci, int slot_id)
 			}
 		}
 	}
+out:
 	/* we are now at a leaf device */
 	xhci_free_virt_device(xhci, slot_id);
 }
-- 
2.15.0-rc2