On Mon, Jun 05, 2023 at 10:57:00AM +0200, Kevin Wolf wrote:
> This series fixes the deadlock that was observed before commit ad128dff
> ('graph-lock: Disable locking for now'), which just disabled the graph
> lock completely as a workaround to get 8.0.1 stable.
>
> In theory the problem is simple: We can't poll while still holding the
> lock of a different AioContext. So bdrv_graph_wrlock() just needs to
> drop that lock before it polls. However, there are a number of callers
> that don't even hold the AioContext lock they are supposed to hold, so
> temporarily unlocking tries to unlock a mutex that isn't locked,
> resulting in assertion failures.
>
> Therefore, much of this series is just for fixing AioContext locking
> correctness. It is only the last two patches that actually fix the
> deadlock and reenable the graph locking.
>
> v2:
> - Fixed patch 2 to actually lock the correct AioContext even if the
> device doesn't support iothreads
> - Improved the commit message for patch 7 [Eric]
> - Fixed mismerge in patch 11 (v1 incorrectly left an #if 0 around)
>
> Kevin Wolf (11):
> iotests: Test active commit with iothread and background I/O
> qdev-properties-system: Lock AioContext for blk_insert_bs()
> test-block-iothread: Lock AioContext for blk_insert_bs()
> block: Fix AioContext locking in bdrv_open_child()
> block: Fix AioContext locking in bdrv_attach_child_common()
> block: Fix AioContext locking in bdrv_reopen_parse_file_or_backing()
> block: Fix AioContext locking in bdrv_open_inherit()
> block: Fix AioContext locking in bdrv_open_backing_file()
> blockjob: Fix AioContext locking in block_job_add_bdrv()
> graph-lock: Unlock the AioContext while polling
> Revert "graph-lock: Disable locking for now"
>
> include/block/graph-lock.h | 6 +-
> block.c | 103 ++++++++++++++++--
> block/graph-lock.c | 42 ++++---
> blockjob.c | 17 ++-
> hw/core/qdev-properties-system.c | 8 +-
> tests/unit/test-block-iothread.c | 7 +-
> .../tests/iothreads-commit-active | 85 +++++++++++++++
> .../tests/iothreads-commit-active.out | 23 ++++
> 8 files changed, 250 insertions(+), 41 deletions(-)
> create mode 100755 tests/qemu-iotests/tests/iothreads-commit-active
> create mode 100644 tests/qemu-iotests/tests/iothreads-commit-active.out
>
> --
> 2.40.1
>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>