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    SubjectRe: [tip:irq/core] genirq: Make nr_irqs runtime expandable
    On Sat, 19 Feb 2011, Yinghai Lu wrote:
    > On 02/19/2011 04:15 AM, tip-bot for Thomas Gleixner wrote:
    > [PATCH] genirq: use IRQ_BITMAP_BITS as search size
    >
    > instead of nr_irqs.
    >
    > Otherwise bitmap_find_next_area could exit with larger start and in extreme
    > case we could fail to get wrong irqs return.
    >
    > For example:
    > IRQ_BITMAP_BITS=10240
    > nr_irqs=8192
    > cnt=2048
    >
    > and bit 0 to bit 8190 are set already.
    >
    > before patch start from bit_find_next_area() will be 8191+2048.
    > later irq_expand_nr_irqs will set nr_irqs 10240.
    > finally irq_alloc_descs will return [8191+2048, 8191+2048+2047] happily..
    >
    > with this patch, will get correct [8191, 8191+2047]

    What a horrible changelog.

    > Signed-off-by: Yinghai Lu <yinghai@kernel.org>
    >
    > ---
    > kernel/irq/irqdesc.c | 5 +++--
    > 1 file changed, 3 insertions(+), 2 deletions(-)
    >
    > Index: linux-2.6/kernel/irq/irqdesc.c
    > ===================================================================
    > --- linux-2.6.orig/kernel/irq/irqdesc.c
    > +++ linux-2.6/kernel/irq/irqdesc.c
    > @@ -346,12 +346,13 @@ irq_alloc_descs(int irq, unsigned int fr
    >
    > mutex_lock(&sparse_irq_lock);
    >
    > - start = bitmap_find_next_zero_area(allocated_irqs, nr_irqs, from, cnt, 0);
    > + start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS,
    > + from, cnt, 0);
    > ret = -EEXIST;
    > if (irq >=0 && start != irq)
    > goto err;
    >
    > - if (start >= nr_irqs) {
    > + if (start + cnt > nr_irqs) {

    One off. That needs to be >= nr_irqs. Good catch otherwise.

    Thanks,

    tglx


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