Subject: Re: [PATCH v3] irqdomain: Prevent Oops in irq_domain_push_irq()
To: Dan Carpenter <dan.carpenter@oracle.com>,
        Marc Zyngier <marc.zyngier@arm.com>,
        David Daney <david.daney@cavium.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        kernel-janitors@vger.kernel.org
References: <20170825121409.6rfv4vt6ztz2oqkt@mwanda>
From: David Daney <ddaney@caviumnetworks.com>
Message-ID: <075689d0-93af-2ff1-d71e-c7914ddd3935@caviumnetworks.com>
Date: Fri, 25 Aug 2017 09:09:57 -0700
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On 08/25/2017 05:14 AM, Dan Carpenter wrote:
> This code generates a Smatch warning:
> 
> 	kernel/irq/irqdomain.c:1511 irq_domain_push_irq()
> 	warn: variable dereferenced before check 'root_irq_data' (see line 1508)
> 
> irq_get_irq_data() does sometimes return NULL pointers so this seems
> like a real bug.  Let's fix this bug by moving the check for NULL
> earlier.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

Thanks for identifying and fixing this.  It looks plausible, so if it 
compiles without error you can add:

Acked-by: David Daney <david.daney@cavium.com>

> ---
> v2: Redo changelog.
> v3: Redo changelog again.  Make it imperative.
> 
> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
> index b9c688944429..e84b7056bb08 100644
> --- a/kernel/irq/irqdomain.c
> +++ b/kernel/irq/irqdomain.c
> @@ -1505,10 +1505,10 @@ int irq_domain_push_irq(struct irq_domain *domain, int virq, void *arg)
>   	if (WARN_ON(!irq_domain_is_hierarchy(domain)))
>   		return -EINVAL;
>   
> -	if (domain->parent != root_irq_data->domain)
> +	if (!root_irq_data)
>   		return -EINVAL;
>   
> -	if (!root_irq_data)
> +	if (domain->parent != root_irq_data->domain)
>   		return -EINVAL;
>   
>   	child_irq_data = kzalloc_node(sizeof(*child_irq_data), GFP_KERNEL,
>