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

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Message-ID: <CACVXFVNCAsM5NihpAFLU5rGo5ynr3=XU5gw7nM5Fi2mrrX+hKA@mail.gmail.com>
Date:	Sat, 23 Jun 2012 00:52:05 +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 12:18 AM, Bjørn Mork <bjorn@...k.no> wrote:
> Ming Lei <tom.leiming@...il.com> writes:

> Yes, intfdata is per interface, but in the case of cdc_ether (and
> probably other similar minidrivers) there are two interfaces pointing to
> the *same* usbnet private data.

Yes, the priv pointers of both interface points to the usbnet instance, but
the same pointer is stored into two places.

>
> What about the situation where disconnect is called simultaneously for
> both interfaces? Or can't that happen? If it can, then we'll do

It can't happen because both parent lock and its lock need to be held in
hotplug situation or unbind situation.

>
>  driver->disconnect(intf1)                driver->disconnect(intf2)
>     dev = usb_get_intfdata(intf1)           dev = usb_get_intfdata(intf2)
>     dev->driver_info->unbind()              dev->driver_info->unbind()
>     net = dev->net                          net = dev->net
>     free_netdev(net)                        free_netdev(dev->net)
>
> where "dev" and "net" will be pointing to the same private data and
> netdevice.

Suppose driver->disconnect(intf1) is called first, .ubind() inside
.disconnect will clear intfdata of another interface(intf2) and call
usb_driver_release_interface(intf2), which will cause .disconnect(intf2)
called, but it will return immediately.

>
> I assume that is what the code above is trying to protect against.  But

I don't see the protection in the code, :-)

> I could be wrong.  That has happened before, believe it or not :-)

Could you provide a link or commit about it?


Thanks,
-- 
Ming Lei
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