[oslo][relmgmt][taskflow][nova] fasteners.ReaderWriterLock and oslo.concurrency's fair lock is broken if used in eventlet

Herve Beraud hberaud at redhat.com
Tue Sep 6 07:41:38 UTC 2022


The oslo patches have been approved, I'll propose a new release, in a
couple of hours, when they will be merged.

Le lun. 5 sept. 2022 à 18:27, Balazs Gibizer <gibi at redhat.com> a écrit :

> Hi,
>
> It is hard to properly figure out which OpenStack project is affected
> exactly. But I want to give a heads up. If the following is true for
> your project then you are affected:
> * using eventlet and
> * using oslo.concurrency fair internal lock (external lock or non fair
> locks are not affected) or using fasteners.ReaderWriterLock directly.
>
> I know that nova is affected and based on code search taskflow is
> affected at least.
>
> The oslo.concurrency's fair lock uses fasteners.ReaderWriterLock[1].
> The fasteners.ReaderWriterLock relies on threading.current_thread to
> identify a thread and decide if a thread already has a lock and
> therefore can reenter the lock. However in an eventlet monkey patched
> environment, a thread that is created with eventlet.spawn_n() or the
> patched threading.Thread() the threading.current_thread call does not
> return an eventlet unique ID. This causes that the lock can be
> reentered from multiple eventlets at the same time.
>
> We have 4 ways forward:
>
> 0) Fix eventlet. There is an open issue in eventlet[3] for this open
> since October 2021. Based on the ticket this direction does not seems
> to feasible.
>
> 1) Sean recently opened an issue[4] on fasteners to restore a
> previously existing workaround that could fix our issues. If an new
> fasteners lib is released with the workaround[5] then at least
> oslo.concurrency requirements needs to be bumped and a new oslo release
> is pushed.
>
> 2) If the fasteners' maintainer does not accept [4][5] in time then I
> have an oslo.concurrency patch[6] that implements a workaround in oslo.
> This also requires a new olso.concurrency release. Also this means that
> projects that are using fasteners.ReaderWriterLock directly need to
> re-implement the fix locally.
>
> 3) If all odds fails I have a nova only patch[7] that implements the
> workaround locally in nova.
>
>
> Note that this issue is present in stable/yoga and on master. On
> stable/xena we uses fasteners < 0.15.0 which is not affected.
>
> Cheers,
> gibi
>
> [1]
>
> https://github.com/openstack/oslo.concurrency/blob/052b2f23572900601b0f41387dbbb07153d88982/oslo_concurrency/lockutils.py#L287-L288
> [2] https://bugs.launchpad.net/oslo.concurrency/+bug/1988311
> [3] https://github.com/eventlet/eventlet/issues/731
> [4] https://github.com/harlowja/fasteners/issues/96
> [5] https://github.com/harlowja/fasteners/pull/97
> [6]
>
> https://review.opendev.org/q/topic:bug/1988311+project:openstack/oslo.concurrency
> [7]
> https://review.opendev.org/q/topic:bug/1988311+project:openstack/nova
>
>
>
>
>

-- 
Hervé Beraud
Senior Software Engineer at Red Hat
irc: hberaud
https://github.com/4383/
https://twitter.com/4383hberaud
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