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

From: Oliver Hartkopp <[email-masked]>
Date: Fri, 31 Jul 2009 13:20:19 +0200

Dave Young wrote:
> On Fri, Jul 31, 2009 at 5:39 PM, Dave Young<[email-masked]> 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<[email-masked]> 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)
> 

Hi Dave,

applied this patch and replaced mdelay(100) with msleep(100).

I got two crashes and three proper boots.

The crashes look like the formerly posted screenshots.
When it boots properly i can see the delay in the boot process.

Does this help?

Regards,
Oliver