linux-kernel - Re: [PATCH v1] irqchip: irq-mips-gic:- Handle return NULL error from ioremap

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Date:   Tue, 17 Jan 2017 10:17:57 +0000
From:   Matt Redfearn <matt.redfearn@...tec.com>
To:     Arvind Yadav <arvind.yadav.cs@...il.com>,
        Marc Zyngier <marc.zyngier@....com>, <tglx@...utronix.de>,
        <jason@...edaemon.net>
CC:     <linux-kernel@...r.kernel.org>,
        Linux MIPS Mailing List <linux-mips@...ux-mips.org>
Subject: Re: [PATCH v1] irqchip: irq-mips-gic:- Handle return NULL error from
 ioremap_nocache



On 17/01/17 10:10, Arvind Yadav wrote:
> Hi Matt,
>
> Please Acknowledge this.
>
> Regards
> Arvind Yadav

Hi Arvind,

Acked-by: Matt Redfearn <matt.redfearn@...tec.com>


>
> On Monday 09 January 2017 02:30 PM, Marc Zyngier wrote:
>> On 09/01/17 08:08, Arvind Yadav wrote:
>>> Here, If ioremap_nocache will fail. It will return NULL.
>>> Kernel can run into a NULL-pointer dereference.
>>> This error check will avoid NULL pointer dereference.
>>>
>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
>>> ---
>>>   drivers/irqchip/irq-mips-gic.c | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/irqchip/irq-mips-gic.c 
>>> b/drivers/irqchip/irq-mips-gic.c
>>> index c01c09e..eeea2e8 100644
>>> --- a/drivers/irqchip/irq-mips-gic.c
>>> +++ b/drivers/irqchip/irq-mips-gic.c
>>> @@ -979,6 +979,8 @@ static void __init __gic_init(unsigned long 
>>> gic_base_addr,
>>>       __gic_base_addr = gic_base_addr;
>>>         gic_base = ioremap_nocache(gic_base_addr, gic_addrspace_size);
>>> +    if (!gic_base)
>>> +        panic("Failed to map GIC memory");
>> So you're replacing a panic due to dereferencing a NULL pointer with
>> another panic -- not much progress here. I appreciate that the message
>> is a bit more explicit, but is there something slightly less drastic we
>> could do? Like returning an error code and see if the kernel otherwise
>> recovers (possibly with reduced functionality)?

Marc, there's really not much that can be done without the GIC 
initializing sucessfully. This should not happen if platform code / 
device tree is set up correctly, so an explicit panic if that is not the 
case is helpful.

Thanks,
Matt

>>
>>>         gicconfig = gic_read(GIC_REG(SHARED, GIC_SH_CONFIG));
>>>       gic_shared_intrs = (gicconfig & GIC_SH_CONFIG_NUMINTRS_MSK) >>
>>>
>> Thanks,
>>
>>     M.
>