Re: [Xen-devel] [PATCH] xen/arm: setup_dt_irq: don't enable the IRQ if the creation has failed

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 01/15/2014 01:44 PM, Ian Campbell wrote:
> On Fri, 2014-01-10 at 20:49 +0000, Julien Grall wrote:
>> For now __setup_dt_irq can only fail if the action is already set.
> 
> Can this ever happen with the current code base?

No, that why I didn't ask for a freeze exception for Xen 4.4.

> 
>> If in the future, the function is updated we don't want to enable the IRQ.
> 
> Such an update is likely to be post-4.4 (unless there is a relationship
> with "IRQ: Protect IRQ to be shared between domains and XEN" AND the RM
> becomes convinced to grant a freeze exception for that patch).
> 
> On that basis this patch could also easily be post-4.4.
>
>> Assuming the function can fail with action = NULL, when Xen will receive the
>> IRQ it will segfault because do_IRQ doesn't check if action is NULL.
> 
> It seems unlikely that the system would be fully functional after such
> an error even with this patch -- it would have failed to register either
> timer, maintenance or the console interrupt.

Timer and maintenance code don't check the return of request_dt_irq
(which call setup_dt_irq).

For the console interrupt, the callback which initialize the interrupt
doesn't return an error... On every serial driver, only an error message
is printed.

In any case, it's wrong to enable this IRQ if the descriptor is not
correctly setup.

> 
>>
>> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
>> ---
>>  xen/arch/arm/gic.c |    4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
>> index e6257a7..62510e3 100644
>> --- a/xen/arch/arm/gic.c
>> +++ b/xen/arch/arm/gic.c
>> @@ -605,8 +605,8 @@ int __init setup_dt_irq(const struct dt_irq *irq, struct 
>> irqaction *new)
>>      rc = __setup_irq(desc, irq->irq, new);
>>      spin_unlock_irqrestore(&desc->lock, flags);
>>  
>> -    desc->handler->startup(desc);
>> -
>> +    if ( !rc )
>> +        desc->handler->startup(desc);
>>  
>>      return rc;
>>  }
> 
> 


-- 
Julien Grall

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