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SubjectRe: Possible regression: MSI vector leakage since 2.6.18-rc5ish (Unable to repeatedly allocate/free MSI interrupt)
Eric W. Biederman wrote:
> Auke Kok <auke-jan.h.kok@intel.com> writes:
>
>> Hi,
>>
>> I've established a regression in the MSI vector/irq allocation routine for both
>> i386 and x86_64. Our test labs repeatedly modprobe/rmmod the e1000 driver for
>> serveral minutes which allocates msi vectors and frees them. These tests have
>> been running fine until 2.6.19.
[snip]
>> I mostly suspect commit 7bd007e480672c99d8656c7b7b12ef0549432c37 at the
>> moment. Perhaps Eric Biederman can help?
>
> Does this patch fix it for you? It looks like i386 vector allocate
> did not have logic to look through the set of vectors more than once.

Yes. A few hundred cycles of loading/unloading snd_hda_intel with enable_msi=1
didn't break it on i386.

I sure hope this can get into 2.6.20!

Auke



> The code in this patch is a simplified version of what we have
> on x86_64.
>
> Eric
>
>
> diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
> index 2424cc9..6a3875f 100644
> --- a/arch/i386/kernel/io_apic.c
> +++ b/arch/i386/kernel/io_apic.c
> @@ -1227,26 +1227,32 @@ static u8 irq_vector[NR_IRQ_VECTORS] __read_mostly = { FIRST_DEVICE_VECTOR , 0 }
>
> static int __assign_irq_vector(int irq)
> {
> - static int current_vector = FIRST_DEVICE_VECTOR, offset = 0;
> - int vector;
> + static int current_vector = FIRST_DEVICE_VECTOR, current_offset = 0;
> + int vector, offset, i;
>
> BUG_ON((unsigned)irq >= NR_IRQ_VECTORS);
>
> if (irq_vector[irq] > 0)
> return irq_vector[irq];
>
> - current_vector += 8;
> - if (current_vector == SYSCALL_VECTOR)
> - current_vector += 8;
> -
> - if (current_vector >= FIRST_SYSTEM_VECTOR) {
> - offset++;
> - if (!(offset % 8))
> - return -ENOSPC;
> - current_vector = FIRST_DEVICE_VECTOR + offset;
> - }
> -
> vector = current_vector;
> + offset = current_offset;
> +next:
> + vector += 8;
> + if (vector >= FIRST_SYSTEM_VECTOR) {
> + offset = (offset + 1) % 8;
> + vector = FIRST_DEVICE_VECTOR + offset;
> + }
> + if (vector == current_vector)
> + return -ENOSPC;
> + if (vector == SYSCALL_VECTOR)
> + goto next;
> + for (i = 0; i < NR_IRQ_VECTORS; i++)
> + if (irq_vector[i] == vector)
> + goto next;
> +
> + current_vector = vector;
> + current_offset = offset;
> irq_vector[irq] = vector;
>
> return vector;
-
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