netdev - Re: [PATCH net] net: qmi_wwan: fix Oops while disconnecting

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Date:	Sat, 23 Jun 2012 11:39:22 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Marius Bjørnstad Kotsbak 
	<marius.kotsbak@...il.com>
Subject: Re: [PATCH net] net: qmi_wwan: fix Oops while disconnecting

Sorry for mistaken triggered sending, :-(

On Sat, Jun 23, 2012 at 11:32 AM, Ming Lei <tom.leiming@...il.com> wrote:
> On Fri, Jun 22, 2012 at 5:11 PM, Bjørn Mork <bjorn@...k.no> wrote:
>
>>
>> Reported-by: Marius Bjørnstad Kotsbak <marius.kotsbak@...il.com>
>> Cc: <stable@...r.kernel.org> # v3.4
>> Signed-off-by: Bjørn Mork <bjorn@...k.no>
>> ---
>>  drivers/net/usb/qmi_wwan.c |    4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
>> index 3767a12..b01960f 100644
>> --- a/drivers/net/usb/qmi_wwan.c
>> +++ b/drivers/net/usb/qmi_wwan.c
>> @@ -197,6 +197,10 @@ err:
>>  static int qmi_wwan_cdc_wdm_manage_power(struct usb_interface *intf, int on)
>>  {
>>        struct usbnet *dev = usb_get_intfdata(intf);
>> +
>> +       /* can be called while disconnecting */
>> +       if (!dev)
>> +               return 0;
>>        return qmi_wwan_manage_power(dev, on);
>>  }
>

Considered there isn't any protection between usbnet_disconnet and
wdm_open/wdm_close, you patch still doesn't work on the race, see
below:

   +       if (!dev)
   +               return 0;

            -> usbnet_disconnect() is triggered and completed here, so
            dev may point to a freed usbnet instance.

             return qmi_wwan_manage_power(dev, on);

One fix I can think of is to export wdm_mutex or its lock/unlock
functions, and introduce the function of qmi_wwan_disconnect, which
will call usbnet_disconnect with holding wdm_mutex.


Thanks,
-- 
Ming Lei
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