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    SubjectRe: [PATCH v5 02/33] genirq: Add irq_alloc_reserved_desc()
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    On Sat, Feb 22, 2014 at 3:38 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
    >
    > OMG, you really mean that:
    >
    > +++ b/arch/alpha/kernel/irq_i8259.c
    > @@ -92,6 +92,7 @@ init_i8259a_irqs(void)
    > outb(0xff, 0xA1); /* mask all of 8259A-2 */
    >
    > for (i = 0; i < 16; i++) {
    > + irq_alloc_desc_at(i, 0);
    > irq_set_chip_and_handler(i, &i8259a_irq_type, handle_level_irq);
    > }
    >
    > You can't be serious about that. There are tons of ways to call into
    > the core and access an irq descriptor aside of irq_set_chip* before it
    > is potentially allocated.
    >
    > Are you going to analyze all of them and add an irq_alloc_desc_at()
    > before that call?
    >
    > HELL, NO!
    >
    > I'm really tired of that.
    >
    > Stay away from kernel/irq/* and wait for people who are competent
    > enough and willing to spend the extra thoughts to come up with
    > solutions which are not completely ass backwards.

    oh, no, sorry for annoying you again.

    In the irq_alloc_desc_at() path for !SPARSE_IRQ, it should not touch anything
    except setting that bit in allocated_irqs bitmap.

    Or could just replace irq_reserve_irq in irq_set_chip(), in that way will avoid
    touching arch codes.

    like

    diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
    index dc04c16..02d6ad0 100644
    --- a/kernel/irq/chip.c
    +++ b/kernel/irq/chip.c
    @@ -28,8 +28,13 @@
    int irq_set_chip(unsigned int irq, struct irq_chip *chip)
    {
    unsigned long flags;
    - struct irq_desc *desc = irq_get_desc_lock(irq, &flags, 0);
    + struct irq_desc *desc;
    +
    +#ifndef CONFIG_SPARSE_IRQ
    + irq_alloc_desc_at(irq, 0);
    +#endif

    + desc = irq_get_desc_lock(irq, &flags, 0);
    if (!desc)
    return -EINVAL;

    @@ -38,12 +43,7 @@ int irq_set_chip(unsigned int irq, struct irq_chip *chip)

    desc->irq_data.chip = chip;
    irq_put_desc_unlock(desc, flags);
    - /*
    - * For !CONFIG_SPARSE_IRQ make the irq show up in
    - * allocated_irqs. For the CONFIG_SPARSE_IRQ case, it is
    - * already marked, and this call is harmless.
    - */
    - irq_reserve_irq(irq);
    +
    return 0;
    }
    EXPORT_SYMBOL(irq_set_chip);

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