Re: [PATCH v2] usb:xhci fix panic in xhci_free_virt_devices_depth_first

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Nov 06, 2017 at 04:20:23PM +0800, Yu Chen wrote:
> From: Yu Chen <chenyu56@huawei.com>
> 
> 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@google.com>
> Signed-off-by: Fan Ning <fanning4@hisilicon.com>
> Signed-off-by: Li Rui <lirui39@hisilicon.com>
> Signed-off-by: yangdi <yangdi10@hisilicon.com>
> Signed-off-by: Yu Chen <chenyu56@huawei.com>
> 
> ---
>  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))

Ok, now you are sending a lot of mess to the kernel log, so what can a
user do about it?

How can this ever happen?  Is it a hardware error, or a kernel driver
logic error?

thanks,

greg k-h