Re: [PATCH v3 for-4.19 1/3] x86/irq: deal with old_cpu_mask for interrupts in movement in fixup_irqs()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.06.2024 18:56, Roger Pau Monne wrote:
> Given the current logic it's possible for ->arch.old_cpu_mask to get out of
> sync: if a CPU set in old_cpu_mask is offlined and then onlined
> again without old_cpu_mask having been updated the data in the mask will no
> longer be accurate, as when brought back online the CPU will no longer have
> old_vector configured to handle the old interrupt source.
> 
> If there's an interrupt movement in progress, and the to be offlined CPU 
> (which
> is the call context) is in the old_cpu_mask clear it and update the mask, so 
> it
> doesn't contain stale data.

Perhaps a comma before "clear" might further help reading. Happy to
add while committing.

> Note that when the system is going down fixup_irqs() will be called by
> smp_send_stop() from CPU 0 with a mask with only CPU 0 on it, effectively
> asking to move all interrupts to the current caller (CPU 0) which is the only
> CPU to remain online.  In that case we don't care to migrate interrupts that
> are in the process of being moved, as it's likely we won't be able to move all
> interrupts to CPU 0 due to vector shortage anyway.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>