linux-kernel - Re: NULL pointer dereference in i2c-hid

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Date:	Thu, 11 Dec 2014 19:16:28 +0100
From:	Gabriele Mazzotta <gabriele.mzt@...il.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	benjamin.tissoires@...hat.com, aduggan@...aptics.com,
	jkosina@...e.cz
Subject: Re: NULL pointer dereference in i2c-hid

On Thursday 11 December 2014 16:03:07 Mika Westerberg wrote:
> On Thu, Dec 11, 2014 at 10:58:01AM +0200, Mika Westerberg wrote:
> > On Wed, Dec 10, 2014 at 06:04:51PM +0100, Gabriele Mazzotta wrote:
> > > my laptop uses a touchpad that needs hid-rmi along with i2c-hid to work.
> > > i2c-hid and hid-rmi can be loaded and unloaded independelty from each
> > > other, however since 34f439e4afcd ("HID: i2c-hid: add runtime PM support")
> > > if I unload hid-rmi and after it I also unload i2c-hid, I get a NULL
> > > pointer dereference.
> > 
> > I'll look into this.
> > 
> > I can reproduce this easily with i2c-hid + hid-multitouch following your
> > directions.
> 
> Can you try the below patch? 
> 
> I think we shouldn't free buffers yet in ->stop() because we need the
> command buffer sending power commands to the device. Also it seems that
> ->start() re-allocates buffers anyway if maximum size increases.
> 
> It shouldn't even leak memory as we release buffers at ->remove()
> anyway.
> 
> diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
> index 62cec01937ea..68a8c938feea 100644
> --- a/drivers/hid/i2c-hid/i2c-hid.c
> +++ b/drivers/hid/i2c-hid/i2c-hid.c
> @@ -705,12 +705,7 @@ static int i2c_hid_start(struct hid_device *hid)
>  
>  static void i2c_hid_stop(struct hid_device *hid)
>  {
> -	struct i2c_client *client = hid->driver_data;
> -	struct i2c_hid *ihid = i2c_get_clientdata(client);
> -
>  	hid->claimed = 0;
> -
> -	i2c_hid_free_buffers(ihid);
>  }
>  
>  static int i2c_hid_open(struct hid_device *hid)

Yes, it works, thanks.

This change seems to also prevent kernel ooops when I unload either
i2c-hid or i2c-designware-platform while the touchpad is in use,
thing that is likely to happen because of the other bug I reported.

Speaking of it, does any of you have any suggestion on how to debug it?
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