On 28/06/2019 12:11, Thomas Gleixner wrote:
> free_irq() ensures that no hardware interrupt handler is executing on a
> different CPU before actually releasing resources and deactivating the
> interrupt completely in a domain hierarchy.
>
> But that does not catch the case where the interrupt is on flight at the
> hardware level but not yet serviced by the target CPU. That creates an
> interesing race condition:
>
> CPU 0 CPU 1 IRQ CHIP
>
> interrupt is raised
> sent to CPU1
> Unable to handle
> immediately
> (interrupts off,
> deep idle delay)
> mask()
> ...
> free()
> shutdown()
> synchronize_irq()
> release_resources()
> do_IRQ()
> -> resources are not available
>
> That might be harmless and just trigger a spurious interrupt warning, but
> some interrupt chips might get into a wedged state.
>
> Utilize the existing irq_get_irqchip_state() callback for the
> synchronization in free_irq().
>
> synchronize_hardirq() is not using this mechanism as it might actually
> deadlock unter certain conditions, e.g. when called with interrupts
> disabled and the target CPU is the one on which the synchronization is
> invoked. synchronize_irq() uses it because that function cannot be called
> from non preemtible contexts as it might sleep.
>
> No functional change intended and according to Marc the existing GIC
> implementations where the driver supports the callback should be able
> to cope with that core change. Famous last words.
I still stand by what I've said! I gave it a go on a small sample of my
home zoo, and nothing caught fire (although it is not exactly easy to
trigger a situation where the additional synchronization would be useful).
>
> Fixes: 464d12309e1b ("x86/vector: Switch IOAPIC to global reservation mode")
> Reported-by: Robert Hodaszi <[email protected]>
> Signed-off-by: Thomas Gleixner <[email protected]>
FWIW:
Reviewed-and-tested-by: Marc Zyngier <[email protected]>
Thanks,
M.
--
Jazz is not dead. It just smells funny...
