Re: [PATCH 0/4] job: Allow complete for jobs on standby

From: Kevin Wolf <kwolf@redhat.com>
To: Max Reitz <mreitz@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
	John Snow <jsnow@redhat.com>,
	qemu-devel@nongnu.org, qemu-block@nongnu.org
Subject: Re: [PATCH 0/4] job: Allow complete for jobs on standby
Date: Fri, 9 Apr 2021 18:15:24 +0200	[thread overview]
Message-ID: <YHB9nKI5x0D+nx5O@merkur.fritz.box> (raw)
In-Reply-To: <20210409120422.144040-1-mreitz@redhat.com>

Am 09.04.2021 um 14:04 hat Max Reitz geschrieben:
> Hi,
> 
> We sometimes have a problem with jobs remaining on STANDBY after a drain
> (for a short duration), so if the user immediately issues a
> block-job-complete, that will fail.
> 
> (See also
> https://lists.nongnu.org/archive/html/qemu-block/2021-04/msg00215.html,
> which this series is an alternative for.)
> 
> Looking at the only implementation of .complete(), which is
> mirror_complete(), it looks like there is basically nothing that would
> prevent it from being run while mirror is paused.  Really only the
> job_enter() at the end, which we should not and need not do when the job
> is paused.
> 
> So make that conditional (patch 2), clean up the function on the way
> (patch 1, which moves one of its blocks to mirror_exit_common()), and
> then we can allow job_complete() on jobs that are on standby (patch 3).
> 
> Patch 4 is basically the same test as in
> https://lists.nongnu.org/archive/html/qemu-block/2021-04/msg00214.html,
> except some comments are different and, well, job_complete() just works
> on STANDBY jobs.
> 
> Patch 5 is an iotest that may or may not show the problem for you.  I’ve
> tuned the numbers so that on my machine, it fails about 50/50 without
> this series (i.e., the job is still on STANDBY and job_complete()
> refuses to do anything).
> 
> I’m not sure we want that iotest, because it does quite a bit of I/O and
> it’s unreliable, and I don’t think there’s anything I can do to make it
> reliable.

Thanks, applied patches 1-4 to the block branch.

Kevin