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

Ming Lei [off-list ref] writes:

On Sat, Jun 23, 2012 at 12:18 AM, Bjørn Mork [off-list ref] wrote:

quoted

Ming Lei [off-list ref] writes:

quoted

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.

quoted

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.

OK, then it can probably go away.  But then again it doesn't do any harm
for any other minidriver.  qmi_wwan is special because of the
cooperation with cdc_wdm.

quoted

 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.

Yes, if that's the only possible call sequence then I agree that
removing the call won't be a problem.  But I don't see much gain either.
And it has been there since the beginning of git history, if that counts
for anything around here.

quoted

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

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

I am trying my best to be positive :-)


Bjørn
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