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Re: [RFC] Xen crashes on ASSERT on suspend/resume, suggested fix
- To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 26 May 2023 09:03:54 +0200
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- Cc: Stefano Stabellini <stefano.stabellini@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, andrew.cooper3@xxxxxxxxxx, xenia.ragiadakou@xxxxxxx, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Fri, 26 May 2023 07:04:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 25.05.2023 21:54, Stefano Stabellini wrote:
> On Thu, 25 May 2023, Jan Beulich wrote:
>> On 25.05.2023 01:51, Stefano Stabellini wrote:
>>> xen/irq: fix races between send_cleanup_vector and _clear_irq_vector
>>
>> This title is, I'm afraid, already misleading. No such race can occur
>> afaict, as both callers of _clear_irq_vector() acquire the IRQ
>> descriptor lock first, and irq_complete_move() (the sole caller of
>> send_cleanup_vector()) is only ever invoked as or by an ->ack()
>> hook, which in turn is only invoked with, again, the descriptor lock
>> held.
>
> Yes I see that you are right about the locking, and thank you for taking
> the time to look into it.
>
> One last question: could it be that a second interrupt arrives while
> ->ack() is being handled? do_IRQ() is running with interrupts disabled?
It is, at least as far as the invocation of ->ack() is concerned. Else
the locking scheme would be broken. You may not that around ->handler()
invocation we enable interrupts.
Jan
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