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

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Message-ID: <87lij7de8u.fsf@nemi.mork.no>
Date:	Thu, 28 Jun 2012 10:36:49 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, Oliver Neukum <oliver@...kum.org>,
	Ming Lei <tom.leiming@...il.com>, linux-usb@...r.kernel.org,
	Marius Bjørnstad Kotsbak 
	<marius.kotsbak@...il.com>
Subject: Re: [PATCH net] net: qmi_wwan: fix Oops while disconnecting

Bjørn Mork <bjorn@...k.no> writes:

[..]
> Fixes this Oops where a cdc-wdm device was closed while the
> USB device was disconnecting, causing wdm_release to call
> qmi_wwan_cdc_wdm_manage_power after intfdata was set to
> NULL by usbnet_disconnect:
>
> [41819.087460] BUG: unable to handle kernel NULL pointer dereference at 00000080
> [41819.087815] IP: [<f8640458>] qmi_wwan_manage_power+0x68/0x90 [qmi_wwan]
> [41819.088028] *pdpt = 000000000314f001 *pde = 0000000000000000
> [41819.088028] Oops: 0002 [#1] SMP

[..]

> 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);
>  }

Hello,

I'd like this patch applied to qmi_wwan regardless of the outcome of the
(now stalled?) generic usbnet_disconnect discussion.

The patch fixes a real Oops in 3.4 and 3.5, and I believe it should be
left in qmi_wwan even if the usbnet code is fixed to avoid this specific
bug.  The additional NULL test won't harm, and it makes the code more
robust should someone decide to rearrange usbnet_disconnect again at
some later point in time.

I really want this fixed in the next 3.4 stable release, if possible.
Should I resubmit the patch, or will you pick it up from
http://patchwork.ozlabs.org/patch/166542/ ?


Thanks,
Bjørn
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