Re: xen: Clear IRQ_GUEST bit from irq_desc status if its action is NULL

[Igor Mammedov <imammedo@redhat.com>]

On 09/13/2011 01:45 PM, Jan Beulich wrote:
>>>> On 13.09.11 at 11:08, Igor Mammedov<imammedo@redhat.com>  wrote:
>> On a system with Intel C600 series Patsburg SAS controller
>> if following command are executed:
>>
>>    rmmod isci
>>    modprobe isci
>>
>> the host will crash in pirq_guest_bind in attempt to dereference
>> NULL action pointer.
>>
>> This is caused by isci driver which does not cleanup irq properly,
>> removing device first and then os tries to unbind its irqs afterwards.
>>
>> c/s 20093 and 20844 fixed host crashes when removing isci module.
>>
>> However in dynamic_irq_cleanup 'action' field of irq_desc is set to
>> NULL but IRQ_GUEST flag in 'status' field is not cleared. So on next
>
> So why don't you clear the bit there?
>
>> attempt to bind pirq (modprobe isci) with IRQ_GUEST flag set, branch
>>    if ( !(desc->status&  IRQ_GUEST) )
>> is skipped and host ends up with dereferencing NULL pointer 'action'.
>>
>> Second hunk is a bit of code cleanup, removing duplicate code and keeps
>> IRQ_GUEST flag reset at one place.
>
> This is not just cleanup - till now, when action == NULL, the function
> would return 0, while with your patch it would return 1 (which is wrong
> afaict), so you'll minimally need to move down the unbind: label by one
> line. But the cleanup here would better be a separate patch anyway.
>
> Jan

Thanks for review.
I'll fix it and re-post it as 2 patches.

>
>> Please review.
>>
>> Signed-off-by: Igor Mammedov<imammedo@redhat.com>
>>
>> diff -r 0312575dc35e xen/arch/x86/irq.c
>> --- a/xen/arch/x86/irq.c	Thu Sep 08 15:13:06 2011 +0100
>> +++ b/xen/arch/x86/irq.c	Tue Sep 13 09:27:12 2011 +0200
>> @@ -1472,6 +1472,7 @@ static irq_guest_action_t *__pirq_guest_
>>
>>       if ( unlikely(action == NULL) )
>>       {
>> +        desc->status&= ~IRQ_GUEST;
>>           dprintk(XENLOG_G_WARNING, "dom%d: pirq %d: desc->action is NULL!\n",
>>                   d->domain_id, pirq->pirq);
>>           return NULL;
>> @@ -1598,17 +1599,14 @@ static int pirq_guest_force_unbind(struc
>>
>>       action = (irq_guest_action_t *)desc->action;
>>       if ( unlikely(action == NULL) )
>> -    {
>> -        dprintk(XENLOG_G_WARNING, "dom%d: pirq %d: desc->action is NULL!\n",
>> -            d->domain_id, pirq->pirq);
>> -        goto out;
>> -    }
>> +        goto unbind;
>>
>>       for ( i = 0; (i<  action->nr_guests)&&  (action->guest[i] != d); i++ )
>>           continue;
>>       if ( i == action->nr_guests )
>>           goto out;
>>
>> + unbind:
>>       bound = 1;
>>       oldaction = __pirq_guest_unbind(d, pirq, desc);
>>
>>
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>
>
>
>
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-- 
Thanks,
  Igor