Re: [discuss] [OOPS] powernow on smp dual core amd64

[Zachary Amsden]

Tom Duffy wrote:

> On Mon, 2005-06-13 at 16:47 -0500, Langsdorf, Mark wrote:
>  
>
> > Okay, I think I have figured this out.  During initialization,
> > the cpufreq infrastruture only initializes the first core of
> > each processor.  When a request comes into the second core,
> > it's data structre is unitialized and we get the null point
> > dereference.
> >
> > The solution is to assign the pointer to the data structure for
> > the first core to all the other cores.
> >
> > Tom, could you try this patch and see if it helps?
> >    
>
> Yes!  It fixed the panic.  I get much further.
>
> Thanks!
>
> Unfortunately, after starting cpuspeed daemon, I get this:
>
> Starting cpuspeed: [  OK  ]
> Starting pcmcia:  Starting PCMCIA services:
> CPU 6: Machine Check Exception:                4 Bank 4: b200000000070f0f
> TSC 4129a3d70d
> Kernel panic - not syncing: Machine check
> <1>Unable to handle kernel NULL pointer dereference at 00000000000000ff RIP:
> [<00000000000000ff>]
>  

asmlinkage void smp_call_function_interrupt(void)
{
       void (*func) (void *info) = call_data->func;
       void *info = call_data->info;
       int wait = call_data->wait;

       ack_APIC_irq();
       /*
        * Notify initiating CPU that I've grabbed the data and am
        * about to execute the function
        */
       mb();
       atomic_inc(&call_data->started);
       /*
        * At this point the info structure may be out of scope unless 
wait==1
        */
       irq_enter();
       (*func)(info);  <--- passed bogus data

Looks like you jumped through a bogus function pointer.  I'm guessing it 
has something to do with an unitialized IRQ vector for the CPU speed on 
one of the cores (simply because it seems somewhat plausible):

extern u8 irq_vector[NR_IRQ_VECTORS];
#define IO_APIC_VECTOR(irq)     (irq_vector[irq])
#define AUTO_ASSIGN             -1

So irq_vector[AUTO_ASSIGN] = 0xff which could have somehow made it into 
your function pointer.

Just a theory.
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