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    SubjectRe: [PATCH] irq/irq_domain: Quit ignoring error returns from irq_alloc_desc_from().
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    On Mon, 09 Apr 2012 09:56:30 -0700, David Daney <ddaney.cavm@gmail.com> wrote:
    > On 04/06/2012 06:26 PM, Grant Likely wrote:
    > > On Thu, 5 Apr 2012 16:52:13 -0700, David Daney<ddaney.cavm@gmail.com> 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;
    > >
    > > Merged, but I've dropped the new variable in favour of making virq an
    > > int. Makes for a smaller diffstat.
    > >
    >
    > Thanks Grant,
    >
    > I had thought about that too, but since virq throughout all the rest of
    > the code is unsigned, I didn't want to introduce an inconsistency.
    >
    > After a little more thought, I think that the domain of virq and the irq
    > used by the rest of the kernel are the same, so it might make sense to
    > change virq to be int universally, and use the kernel convention that
    > negative numbers indicate error conditions. But that would be a much
    > larger patch.

    ... touching pretty much *every* driver in the kernel! Blech!

    Yeah, that's not going to happen. As a rule, irq numbers are always
    unsigned, but there are a few apis that can return either '0' meaning
    no irq, or a negative value indicating an error. The irq_alloc_desc
    apis unfortunately are one such case.

    g.



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