linux-kernel - Re: [PATCH] irqchip/gic: check return value of of_address_to

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Date:   Thu, 5 Jul 2018 12:32:22 -0700
From:   Bo Yan <byan@...dia.com>
To:     Marc Zyngier <marc.zyngier@....com>
CC:     <tglx@...utronix.de>, <jason@...edaemon.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irqchip/gic: check return value of of_address_to_resource

Marc,

Sorry for the previous reply. My email settings were not correct, so it 
inserted those confidentiality text, which was not what I intended.

This is what I think:

diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index ced10c4..0b60bb0 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -1284,7 +1284,7 @@ static bool gic_check_eoimode(struct device_node 
*node, void __iomem **base)
  {
         struct resource cpuif_res;

-       of_address_to_resource(node, 1, &cpuif_res);
+       (void)of_address_to_resource(node, 1, &cpuif_res);

         if (!is_hyp_mode_available())
                 return false;

We are 100% sure of_address_to_resource will succeed in this particular 
case, so "(void)" will help suppress Coverity warning.

On 07/05/2018 12:18 PM, Bo Yan wrote:
> Marc,
> 
> I'm also wondering if of_address_to_resource can really fail in this 
> particular case?
> 
> What if we just explicitly discard the return value like this:
> 
> (void)of_address_to_resource(node, 1, &cpuif_res);
> 
> This suppresses Coverity warning by explicitly stating we are 100% sure 
> the function call will always return success.
> 
> On 07/05/2018 12:13 PM, Marc Zyngier wrote:
>> Hi Bo,
>>
>> On Thu, 5 Jul 2018 11:20:59 -0700
>> Bo Yan <byan@...dia.com> wrote:
>>
>>> The of_address_to_resource returns 0 if successful. gic_check_eoimode
>>> calls it without checking the return value. This induces Coverity
>>> warning: "Unchecked return value".
>>>
>>> Return false from gic_check_eoimode if of_address_to_resource returns
>>> non-0 value.
>>>
>>> Signed-off-by: Bo Yan <byan@...dia.com>
>>> ---
>>>   drivers/irqchip/irq-gic.c | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
>>> index ced10c4..0bceb10 100644
>>> --- a/drivers/irqchip/irq-gic.c
>>> +++ b/drivers/irqchip/irq-gic.c
>>> @@ -1284,7 +1284,8 @@ static bool gic_check_eoimode(struct 
>>> device_node *node, void __iomem **base)
>>>   {
>>>       struct resource cpuif_res;
>>> -    of_address_to_resource(node, 1, &cpuif_res);
>>> +    if (of_address_to_resource(node, 1, &cpuif_res))
>>> +        return false;
>>
>> We've just done an of_iomap() on this resource, which succeeded. How
>> can the same thing now fail? It would mean that the device tree has
>> been pulled from under our feet...
>>
>> And if it could happen, why is returning false the right thing to do?
>> Why would we say we want EOImode==0 instead of 1?
>>
>>>       if (!is_hyp_mode_available())
>>>           return false;
>>
>> As it stands, I'm not taking such a patch. It either papers over a
>> bigger problem, or just keeps a warning quiet for the sake of it.
>>
>> Thanks,
>>
>>     M.
>>