Re: [Qemu-devel] [PATCH for 2.9 v3 00/10] block: Fixes regarding dataplane and management operations

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Apr 10, 2017 at 11:05:32PM +0800, Fam Zheng wrote:
> v3: Respin the unmerged changes from v2 and include one new fix:
> 
>     (Yes, it is a big series for the last -rc, and I personally prefer the v2
>     approach for the 4-9 part of the problem, which is much more mechanical.)
> 
>     - 1, 2 are redoing previous patch 4, using bdrv_parent_drained_begin/end.
>       [Kevin]
>       Also fix the ordering against aio_context_release. [Stefan]
>     - 3 is unchanged from patch 6 in v2.
>     - 4-9 are reworking of patch 5 following Paolo's suggestion, which allowed
>       better patch split.
>     - 10 is finding of a latent bug, which is revealed by patch 9.
> 
> v2: - Drop patch 4 in v1. A second thought made me feel neither it nor Kevin's
>       suggestion to move the BH process to bdrv_drain_recurse/BDRV_POLL_WHILE
>       is a complete fix. So leave it for a separate patch.
>     - Add rev-by to patches 1, 3, 4.
>     - Split from patch 1 in v1 and add patch 2, for the new assertions. [Kevin]
>     - Rewrite patch 5. Fix block job's co when a BDS is moved to a different
>       aio context. [Kevin]
>     - Add patch 6.
> 
> Crashes are reported on dataplane devices when doing snapshot and commit under
> guest I/O.
> 
> With this series, Ed's test case '176' now passes:
> 
>     https://github.com/skyportsystems/qemu-1/commits/eswierk-iotests-2.9
> 
> Fam Zheng (10):
>   block: Make bdrv_parent_drained_begin/end public
>   block: Quiesce old aio context during bdrv_set_aio_context
>   tests/block-job-txn: Don't start block job before adding to txn
>   coroutine: Extract qemu_aio_coroutine_enter
>   async: Introduce aio_co_enter and aio_co_enter_if_inactive
>   block: Introduce bdrv_coroutine_enter and *_if_inactive
>   blockjob: Use bdrv_coroutine_enter to start coroutine
>   qemu-io-cmds: Use bdrv_coroutine_enter
>   block: Use bdrv_coroutine_enter to start I/O coroutines
>   block: Fix bdrv_co_flush early return
> 
>  block.c                    | 17 +++++++++++++++--
>  block/block-backend.c      |  4 ++--
>  block/io.c                 | 34 ++++++++++++++++++----------------
>  blockjob.c                 |  4 ++--
>  include/block/aio.h        | 18 ++++++++++++++++++
>  include/block/block.h      | 27 +++++++++++++++++++++++++++
>  include/qemu/coroutine.h   |  5 +++++
>  qemu-io-cmds.c             |  2 +-
>  tests/qemu-iotests/109.out | 10 +++++-----
>  tests/test-blockjob-txn.c  |  6 +++++-
>  util/async.c               | 14 +++++++++++++-
>  util/qemu-coroutine.c      | 11 ++++++++---
>  util/trace-events          |  2 +-
>  13 files changed, 120 insertions(+), 34 deletions(-)

We need a fix for 2.9.  Interactions between AioContexts, coroutines,
and blockjobs are complex and brittle.  That is a pre-existing problem
though and hopefully we can simplify abstractions in 2.10.

Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

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