Re: [Qemu-devel] [PATCH v2 0/6] jobs: fix transactional race condition (For-2.8 ?)

From: John Snow <jsnow@redhat.com>
To: qemu-block@nongnu.org
Cc: kwolf@redhat.com, vsementsov@virtuozzo.com, jcody@redhat.com,
	qemu-devel@nongnu.org, stefanha@redhat.com, pbonzini@redhat.com
Subject: Re: [Qemu-devel] [PATCH v2 0/6] jobs: fix transactional race condition (For-2.8 ?)
Date: Thu, 27 Oct 2016 12:08:47 -0400	[thread overview]
Message-ID: <98549108-d198-4d89-949a-73b81cba42e7@redhat.com> (raw)
In-Reply-To: <1477342593-30707-1-git-send-email-jsnow@redhat.com>

Ping?

On 10/24/2016 04:56 PM, John Snow wrote:
> Requires: [Qemu-devel] [PATCH 0/7] blockjobs: preliminary refactoring work, Pt 1
>
> There are a few problems with transactional job completion right now.
>
> First, if jobs complete so quickly they complete before remaining jobs
> get a chance to join the transaction, the completion mode can leave well
> known state and the QLIST can get corrupted and the transactional jobs
> can complete in batches or phases instead of all together.
>
> Second, if two or more jobs defer to the main loop at roughly the same
> time, it's possible for one job's cleanup to directly invoke the other
> job's cleanup from within the same thread, leading to a situation that
> will deadlock the entire transaction.
>
> Thanks to Vladimir for pointing out these modes of failure.
>
> I have omitted the test for right now, but wanted to air the patches on-list.
> It makes no attempt to change the locking mechanisms around qmp_transaction
> right now, asserting instead that things are no more broken than they were,
> especially in the case of dataplane. I will make further attempts to clarify
> the locking mechanisms around qmp_transaction after Paolo's changes go in.
>
> ===
> v2:
> ===
>
> - Correct Vladimir's email (Sorry!)
> - Add test as a variant of an existing test [Vladimir]
>
> ________________________________________________________________________________
>
> For convenience, this branch is available at:
> https://github.com/jnsnow/qemu.git branch job-fix-race-condition
> https://github.com/jnsnow/qemu/tree/job-fix-race-condition
>
> This version is tagged job-fix-race-condition-v2:
> https://github.com/jnsnow/qemu/releases/tag/job-fix-race-condition-v2
>
> John Snow (5):
>   blockjob: add .clean property
>   blockjob: add .start field
>   blockjob: add block_job_start
>   blockjob: refactor backup_start as backup_job_create
>   iotests: add transactional failure race test
>
> Vladimir Sementsov-Ogievskiy (1):
>   blockjob: fix dead pointer in txn list
>
>  block/backup.c               | 59 +++++++++++++++++--------------
>  block/commit.c               |  4 +--
>  block/mirror.c               |  5 +--
>  block/replication.c          | 12 ++++---
>  block/stream.c               |  4 +--
>  blockdev.c                   | 83 ++++++++++++++++++++++++++++----------------
>  blockjob.c                   | 55 ++++++++++++++++++++++-------
>  include/block/block_int.h    | 23 ++++++------
>  include/block/blockjob.h     |  9 +++++
>  include/block/blockjob_int.h | 11 ++++++
>  tests/qemu-iotests/124       | 53 ++++++++++++++++++----------
>  tests/qemu-iotests/124.out   |  4 +--
>  tests/test-blockjob-txn.c    | 12 +++----
>  13 files changed, 219 insertions(+), 115 deletions(-)
>