Re: [PATCH 00/21] Graph locking part 4 (node management)

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, Aug 17, 2023 at 02:49:59PM +0200, Kevin Wolf wrote:
> The previous parts of the graph locking changes focussed mostly on the
> BlockDriver side and taking reader locks while performing I/O. This
> series focusses more on the functions managing the graph structure, i.e
> adding, removing and replacing nodes and updating their permissions.
> 
> Many of these places actually need to take the writer lock to avoid
> readers seeing an inconsistent half-updated graph state. Therefore
> taking the writer lock is now pushed down from the very low-level
> function bdrv_replace_child_noperm() into its more high level callers.

The word "down" confuses me. It seems like the direction is up instead
of down and the scope of the lock is increasing rather than decreasing.
But I haven't read the actual patches yet...

> 
> Kevin Wolf (21):
>   block: Remove unused BlockReopenQueueEntry.perms_checked
>   preallocate: Factor out preallocate_truncate_to_real_size()
>   preallocate: Don't poll during permission updates
>   block: Take AioContext lock for bdrv_append() more consistently
>   block: Introduce bdrv_schedule_unref()
>   block-coroutine-wrapper: Add no_co_wrapper_bdrv_wrlock functions
>   block-coroutine-wrapper: Allow arbitrary parameter names
>   block: Mark bdrv_replace_child_noperm() GRAPH_WRLOCK
>   block: Mark bdrv_replace_child_tran() GRAPH_WRLOCK
>   block: Mark bdrv_attach_child_common() GRAPH_WRLOCK
>   block: Call transaction callbacks with lock held
>   block: Mark bdrv_attach_child() GRAPH_WRLOCK
>   block: Mark bdrv_parent_perms_conflict() and callers GRAPH_RDLOCK
>   block: Mark bdrv_get_cumulative_perm() and callers GRAPH_RDLOCK
>   block: Mark bdrv_child_perm() GRAPH_RDLOCK
>   block: Mark bdrv_parent_cb_change_media() GRAPH_RDLOCK
>   block: Take graph rdlock in bdrv_drop_intermediate()
>   block: Take graph rdlock in bdrv_change_aio_context()
>   block: Mark bdrv_root_unref_child() GRAPH_WRLOCK
>   block: Mark bdrv_unref_child() GRAPH_WRLOCK
>   block: Mark bdrv_add/del_child() and caller GRAPH_WRLOCK
> 
>  include/block/block-common.h                |   4 +
>  include/block/block-global-state.h          |  30 +-
>  include/block/block_int-common.h            |  34 +-
>  include/block/block_int-global-state.h      |  14 +-
>  include/sysemu/block-backend-global-state.h |   4 +-
>  block.c                                     | 340 ++++++++++++++------
>  block/blklogwrites.c                        |   4 +
>  block/blkverify.c                           |   2 +
>  block/block-backend.c                       |  29 +-
>  block/copy-before-write.c                   |  10 +-
>  block/crypto.c                              |   6 +-
>  block/graph-lock.c                          |  23 +-
>  block/mirror.c                              |   8 +
>  block/preallocate.c                         | 133 +++++---
>  block/qcow2.c                               |   4 +-
>  block/quorum.c                              |  23 +-
>  block/replication.c                         |   9 +
>  block/snapshot.c                            |   2 +
>  block/stream.c                              |  20 +-
>  block/vmdk.c                                |  13 +
>  blockdev.c                                  |  23 +-
>  blockjob.c                                  |   2 +
>  tests/unit/test-bdrv-drain.c                |  23 +-
>  tests/unit/test-bdrv-graph-mod.c            |  20 ++
>  tests/unit/test-block-iothread.c            |   3 +
>  scripts/block-coroutine-wrapper.py          |  18 +-
>  tests/qemu-iotests/051.pc.out               |   6 +-
>  27 files changed, 580 insertions(+), 227 deletions(-)
> 
> -- 
> 2.41.0
> 

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