netdev - Re: tty_register_device NULL pointer dereference in 2.6.31-rc4

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Date:	Fri, 31 Jul 2009 18:10:21 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Oliver Hartkopp <oliver@...tkopp.net>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Marcel Holtmann <marcel@...tmann.org>,
	Linux Netdev List <netdev@...r.kernel.org>,
	linux-bluetooth@...r.kernel.org
Subject: Re: tty_register_device NULL pointer dereference in 2.6.31-rc4

On Fri, Jul 31, 2009 at 5:39 PM, Dave Young<hidave.darkstar@...il.com> wrote:
> On Thu, Jul 30, 2009 at 12:05:55PM +0200, Oliver Hartkopp wrote:
>> Dave Young wrote:
>> > On Wed, Jul 29, 2009 at 10:00 PM, Oliver Hartkopp<oliver@...tkopp.net> wrote:
>> >> Hi Dave,
>> >>
>> >> i got it again - even with your patch (that's why it's 2.6.31-rc4-dirty in the
>> >> attached screenshot).
>> >
>> > Weird, the oops occurs between sock init and tty init routines. Could
>> > you tell your bluez version and your configuration?
>> >
>>
>> No problem:
>
> Thanks.
>
> It's still reasonable, after rfcomm sock layer initialized, userspace do sock ioctl callback but tty layer was not initilized yet at this time.
>
> Could you confirm it by applying following debug patch on top of my previous patch? if you get more oops with it then above reason will be right.
>
> --- linux-2.6.orig/net/bluetooth/rfcomm/core.c  2009-07-31 17:14:07.000000000 +0800
> +++ linux-2.6/net/bluetooth/rfcomm/core.c       2009-07-31 17:30:39.000000000 +0800
> @@ -36,6 +36,7 @@
>  #include <linux/net.h>
>  #include <linux/mutex.h>
>  #include <linux/kthread.h>
> +#include <linux/nmi.h>
>
>  #include <net/sock.h>
>  #include <asm/uaccess.h>
> @@ -2080,7 +2081,7 @@ static CLASS_ATTR(rfcomm_dlc, S_IRUGO, r
>  /* ---- Initialization ---- */
>  static int __init rfcomm_init(void)
>  {
> -       int ret;
> +       int ret, i;
>
>        l2cap_load();
>
> @@ -2088,6 +2089,12 @@ static int __init rfcomm_init(void)
>        if (ret)
>                goto out_sock;
>
> +       /* delay 5 seconds to trigger the tty bug */
> +       for (i = 0; i < 50; i++) {
> +               touch_nmi_watchdog();
> +               mdelay(100);

Hi, for this case, msleep is better, you can just replace the above
two lines with msleep(100)

> +       }
> +
>        ret = rfcomm_init_ttys();
>        if (ret)
>                goto out_tty;
>



-- 
Regards
dave
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