linux-kernel - Re: [OOPS s390] Unable to handle kernel pointer dereference at virtual kernel address (null)

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Message-ID: <248142179.74791.1303353294865.JavaMail.root@md01.wow.synacor.com>
Date:	Wed, 20 Apr 2011 22:34:54 -0400 (EDT)
From:	Stephen Powell <zlinuxman@...way.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Jan Glauber <jang@...ux.vnet.ibm.com>,
	Jonathan Nieder <jrnieder@...il.com>,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
	622570@...s.debian.org
Subject: Re: [OOPS s390] Unable to handle kernel pointer dereference at
 virtual kernel address (null)

On Mon, 18 Apr 2011 07:51:41 -0400 (EDT), Heiko Carstens wrote:
> 
> That's a bug in the pfault interrupt code. After a cleanup patch which
> simplified lowcore accesses we are left with a dereference which shouldn't
> be there.  The patch below should fix it.
> The bug was introduced with 2.6.37-rc1.
> 
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index 9217e33..4cf85fe 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -558,9 +558,9 @@ static void pfault_interrupt(unsigned int ext_int_code,
>  	 * Get the token (= address of the task structure of the affected task).
>  	 */
>  #ifdef CONFIG_64BIT
> -	tsk = *(struct task_struct **) param64;
> +	tsk = (struct task_struct *) param64;
>  #else
> -	tsk = *(struct task_struct **) param32;
> +	tsk = (struct task_struct *) param32;
>  #endif
>  
>  	if (subcode & 0x0080) {

I applied the above patch and re-built the kernel.  I did not apply
Jan Glauber's suggested patch, since Heiko's suggested patch seemed to be a
"direct hit".  I have had the server up for more than 24 hours now,
which is definitely a good sign.  Without this patch, I've not been able
to keep a 2.6.38 s390x kernel up for more than a few hours.  Unfortunately,
since I can't reproduce the problem on demand, I cannot say with 100%
certainty that the problem is fixed, but it looks good and makes sense.

-- 
  .''`.     Stephen Powell    
 : :'  :
 `. `'`
   `-
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