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Old 04-21-2011, 02:34 AM
Stephen Powell
 
Default Bug#622570: 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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