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Re: [PATCH v2] x86/irq: do not release irq until all cleanup is done
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 17 Nov 2022 10:13:05 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 17 Nov 2022 09:13:21 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.11.2022 13:21, Roger Pau Monne wrote:
> Current code in _clear_irq_vector() will mark the irq as unused before
> doing the cleanup required when move_in_progress is true.
>
> This can lead to races in create_irq() if the function picks an irq
> desc that's been marked as unused but has move_in_progress set, as the
> call to assign_irq_vector() in that function can then fail with
> -EAGAIN.
>
> Prevent that by only marking irq descs as unused when all the cleanup
> has been done. While there also use write_atomic() when setting
> IRQ_UNUSED in _clear_irq_vector() and add a barrier in order to
> prevent the setting of IRQ_UNUSED getting reordered by the compiler.
>
> The check for move_in_progress cannot be removed from
> _assign_irq_vector(), as other users (io_apic_set_pci_routing() and
> ioapic_guest_write()) can still pass active irq descs to
> assign_irq_vector().
>
> Note the trace point is not moved and is now set before the irq is
> marked as unused. This is done so that the CPU mask provided in the
> trace point is the one belonging to the current vector, not the old
> one.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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