Re: [PATCH] irq/irq_domain: Quit ignoring error returns from irq_alloc_desc_from().

[Rob Herring <robherring2@gmail.com>]

On 04/05/2012 06:52 PM, David Daney wrote:
> From: David Daney <david.daney@cavium.com>
> 
> In commit 4bbdd45a (irq_domain/powerpc: eliminate irq_map; use
> irq_alloc_desc() instead) code was added that ignores error returns
> from irq_alloc_desc_from() by (silently) casting the return value to
> unsigned.  The negitive value error return now suddenly looks like a
> valid irq number.
> 
> Commits cc79ca69 (irq_domain: Move irq_domain code from powerpc to
> kernel/irq) and 1bc04f2c (irq_domain: Add support for base irq and
> hwirq in legacy mappings) move this code to its current location in
> irqdomain.c
> 
> The result of all of this is a null pointer dereference OOPS if one of
> the error cases is hit.
> 
> The fix: Don't cast away the negativeness of the return value and then
> check for errors.
> 
> Signed-off-by: David Daney <david.daney@cavium.com>
> ---
>  kernel/irq/irqdomain.c |   11 ++++++-----
>  1 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
> index af48e59..9d3e3ae 100644
> --- a/kernel/irq/irqdomain.c
> +++ b/kernel/irq/irqdomain.c
> @@ -351,6 +351,7 @@ unsigned int irq_create_mapping(struct irq_domain *domain,
>                               irq_hw_number_t hwirq)
>  {
>       unsigned int virq, hint;
> +     int irq;
>  
>       pr_debug("irq: irq_create_mapping(0x%p, 0x%lx)\n", domain, hwirq);
>  
> @@ -380,14 +381,14 @@ unsigned int irq_create_mapping(struct irq_domain 
> *domain,
>       hint = hwirq % irq_virq_count;
>       if (hint == 0)
>               hint++;
> -     virq = irq_alloc_desc_from(hint, 0);

You are not looking at mainline. hint was removed in later versions, and
the referenced commit ids don't exist.

Rob

> -     if (!virq)
> -             virq = irq_alloc_desc_from(1, 0);
> -     if (!virq) {
> +     irq = irq_alloc_desc_from(hint, 0);
> +     if (irq <= 0)
> +             irq = irq_alloc_desc_from(1, 0);
> +     if (irq <= 0) {
>               pr_debug("irq: -> virq allocation failed\n");
>               return 0;
>       }
> -
> +     virq = irq;
>       if (irq_setup_virq(domain, virq, hwirq)) {
>               if (domain->revmap_type != IRQ_DOMAIN_MAP_LEGACY)
>                       irq_free_desc(virq);