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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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