Re: [PATCH 2/2] x86_64 irq: Handle irqs pending in IRR during irq migration.

[Andrew Morton <akpm@osdl.org>]

On Fri, 02 Feb 2007 17:35:31 -0700
ebiederm@xmission.com (Eric W. Biederman) wrote:

> When making the interrupt vectors per cpu I failed to handle a case
> during irq migration.  If the same interrupt comes in while we are
> servicing the irq but before we migrate it the pending bit in the
> local apic IRR register will be set for that irq.
> 
> After migrating the irq to another cpu and or vector the data
> structures will no longer be setup to handle this pending irq.  Then as
> soon as we return from servicing the irq we just migrated we will get
> a nasty: "No irq handler for vector" message. 
> 
> Since we do not disable irqs for edge triggered interrupts except
> in the smallest possible window during migration I cannot avoid
> migrating an irq in the unlikely event that it becomes pending.
> This is because by the time the irq could no longer become pending
> I have already updated all of my data structures.
> 
> Therefore this patch introduces an intermediate state that
> exists soley on the cpu where we are handling the irq during
> migration.  The irq number is changed to negative in the
> vector_irq data structure.
> 
> Once the migration operation is complete we know we will receive
> no more interrupts on this vector so the irq pending state for
> this irq will no longer be updated.  If the irq is not pending and
> we are in the intermediate state we immediately free the vector,
> otherwise in we free the vector in do_IRQ when the pending irq
> arrives.

So is this a for-2.6.20 thing?  The bug was present in 2.6.19, so
I assume it doesn't affect many people?