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

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Message-ID: <CACVXFVOZUvyNDzEoWT5o7JQRKjuw1pUgkipxV7dxT1w2Dd0H+A@mail.gmail.com>
Date:	Sat, 23 Jun 2012 22:55:13 +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

On Sat, Jun 23, 2012 at 4:45 PM, Bjørn Mork <bjorn@...k.no> wrote:

> 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.

Thanks for your explanation.

I see, and your patch is correct, but it might not be generic enough.

So driver_info->unbind will sync with .open/.close of the subdriver,
just like unregister_netdev will sync with .open/.close of usbnet interface.

IMO, the general solution is to keep intfdata's lifetime after ->unbind,
which can guarantee that intfdata can be accessed safely in .open/.close
of usbnet interface and the other subdrivers' device.

Suppose there will be another usbnet driver which has its own subdriver
too, the same trick of checking need to be added again if not taking the
general way of simply removing 'usb_set_intfdata(intf, NULL);' in
usbnet_disconnect.

Thanks,
-- 
Ming Lei
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