linux-kernel - Re: [PATCH] Re: [2.6.26] OOPS in __linkwatch_run_queue (unable to handle kernel NULL pointer dereference at 00000235)

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Date:	Mon, 17 Nov 2008 09:11:08 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	folkert@...heusden.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Re: [2.6.26] OOPS in __linkwatch_run_queue (unable to
	handle kernel NULL pointer dereference at 00000235)

On Mon, Nov 17, 2008 at 12:50:25AM -0800, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Mon, 17 Nov 2008 08:40:58 +0000
> 
> > net: link_watch: Don't add a linkwatch event before register_netdev()
> > 
> > b44 and some other network drivers run netif_carrier_off() before
> > register_netdev(). Then, if register fails, free_netdev() destruction
> > is done while dev is still referenced and held on the lweventlist.
> > 
> > Of course, it would be nice if all drivers could use some common order
> > of calling things like register_netdev() vs. netif_carrier_off(), but
> > since there is a lot of this I guess there is probably some reason,
> > so this patch doesn't change the order but assumes that such an early
> > netif_carrier_off() is only to set the __LINK_STATE_NOCARRIER flag,
> > and some netif_carrier_on()/_off() will still follow.
> > 
> > Reported-by: Folkert van Heusden <folkert@...heusden.com>
> > Signed-off-by: Jarek Poplawski <jarkao2@...il.com>
> 
> Ugh, drivers should not be fiddling with stuff like this before the
> device object is even registered.
> 
> I can just imagine all sorts of other operations drivers might find
> it "convenient" to do before the sucker is even registered, causing
> similar if not even worse problems.
> 
> It's pretty simple, make netif_carrier_off() be the first thing
> ->open() does and make it the last thing ->stop() and ->suspend()
> do.  That's how to fix this bug.
> 
> I'm going to fix this as follows.  B44 already abided by 2/3 of
> this by handling the ->stop() and ->suspend() cases correctly already.
> 
> b44: Do not call netif_carrier_off() before device is even registered.
> 
> This is illegal.  Instead simply do this first thing in ->open().

Yes, this looks very nice! But this should be done in "a few" more
drivers, like cxgb3 etc.

Jarek P.

PS: I think "Reported-by" could stay anyway.

> Signed-off-by: David S. Miller <davem@...emloft.net>
> 
> diff --git a/drivers/net/b44.c b/drivers/net/b44.c
> index c3bda5c..2e353b8 100644
> --- a/drivers/net/b44.c
> +++ b/drivers/net/b44.c
> @@ -1426,6 +1426,8 @@ static int b44_open(struct net_device *dev)
>  	struct b44 *bp = netdev_priv(dev);
>  	int err;
>  
> +	netif_carrier_off(dev);
> +
>  	err = b44_alloc_consistent(bp, GFP_KERNEL);
>  	if (err)
>  		goto out;
> @@ -2165,8 +2167,6 @@ static int __devinit b44_init_one(struct ssb_device *sdev,
>  	dev->irq = sdev->irq;
>  	SET_ETHTOOL_OPS(dev, &b44_ethtool_ops);
>  
> -	netif_carrier_off(dev);
> -
>  	err = ssb_bus_powerup(sdev->bus, 0);
>  	if (err) {
>  		dev_err(sdev->dev,
--
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