Re: [PATCH] x86/IRQ: fix valid-old-vector checks in __assign_irq_vector()

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 27/09/12 15:50, Jan Beulich wrote:
> There are two greater-than-zero checks for the old vector retrieved,
> which don't work when a negative value got stashed into the respective
> arch_irq_desc field. The effect of this was that for interrupts that
> are intended to get their affinity adjusted the first time before the
> first interrupt occurs, the affinity change would fail, because the
> original vector assignment would have caused the move_in_progress flag
> to get set (which causes subsequent re-assignments to fail until it
> gets cleared, which only happens from the ->ack() actor, i.e. when an
> interrupt actually occurred).
>
> This addresses a problem introduced in c/s 23816:7f357e1ef60a (by
> changing IRQ_VECTOR_UNASSIGNED from 0 to -1).
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> I have to admit that I don't understand why the value got changed in
> the first place: 0 is as invalid a value as -1 for a vector to be used
> for delivering hardware interrupts.

http://lists.xen.org/archives/html/xen-devel/2011-09/msg00193.html

It was a suggestion for consistency with using -1 elsewhere in the irq
code to mean unassigned.

~Andrew

>
> --- 2012-09-21.orig/xen/arch/x86/irq.c	2012-09-19 08:48:33.000000000 +0200
> +++ 2012-09-21/xen/arch/x86/irq.c	2012-09-27 13:33:45.000000000 +0200
> @@ -430,8 +430,7 @@ static int __assign_irq_vector(
>       * 0x80, because int 0x80 is hm, kind of importantish. ;)
>       */
>      static int current_vector = FIRST_DYNAMIC_VECTOR, current_offset = 0;
> -    unsigned int old_vector;
> -    int cpu, err;
> +    int cpu, err, old_vector;
>      cpumask_t tmp_mask;
>      vmask_t *irq_used_vectors = NULL;
>  
>
>
>

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com