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

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Message-ID: <8762aiju27.fsf@nemi.mork.no>
Date:	Sat, 23 Jun 2012 10:45:04 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	Ming Lei <tom.leiming@...il.com>
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

Ming Lei <tom.leiming@...il.com> writes:
> 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);


usbnet_disconnect() cannot continue to the point where it frees the
netdev before wdm_open/wdm_close has completed, because it waits for
qmi_wwan_unbind which waits for wdm_disconnect.  And wdm_disconnect
takes the both read and write mutexes.

So I do not think there is any race there.  



Bjørn
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