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bug#32786: (system* ...) call somehow interferes with atomic-box on armv
From: |
Михаил Бахтерев |
Subject: |
bug#32786: (system* ...) call somehow interferes with atomic-box on armv7l |
Date: |
Thu, 27 Sep 2018 11:18:16 +0500 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
Thanks for clarification! I'll be able to test the patch in a couple of
days.
- MB. Respectfully
On Thu, Sep 27, 2018 at 01:49:23AM -0400, Mark H Weaver wrote:
> Hi,
>
> Thanks for the additional details. I was able to reproduce the bug, and
> I believe I now see the problem.
>
> 'atomic-box-compare-and-swap!' is implemented using
> 'atomic_compare_exchange_weak' (if available), but neglects to handle
> the case where 'atomic_compare_exchange_weak' may spuriously fail. In
> that case, the box is left unchanged, although the observed value was
> equal to the expected value.
>
> What's happening here is that the 'atomic-box-compare-and-swap!' in
> 'sleep-loop' fails spuriously, leaving the box in state #:accepted
> although it returns #:accepted as its result. When the main loop
> discovers this, it changes the state to #:need-to-sleep, although the
> thread has already ended.
>
> To confirm this hypothesis, I added a print statement to the main loop
> showing the state of the box that it observed during the protocol
> exchange, and indeed it sees #:accepted the first time it checks, and
> #:need-to-sleep in all later iterations.
>
> I've attached a proposed patch that I hope will fix this problem. If
> you'd be willing to test it, I'd be grateful, but otherwise I'll try to
> test it in the next week or so. My access to armv7l boxes is somewhat
> limited.
>
> Thanks for this report.
>
> Mark
>
>