qmp_block_dirty_bitmap_add() and the incoming-migration bitmap loader both create a persistent bitmap with bdrv_create_dirty_bitmap(), which always creates it writable, without checking whether the node can actually be written to. A persistent bitmap added to an already read-only or inactive node stays writable in memory on a node that can never store it, and the next global inactivation (migration completion, save, or any other bdrv_inactivate_all() caller) fails trying to flush it back:
Lost persistent bitmaps during inactivation of node '<node>': No write access migration_block_inactivate: bdrv_inactivate_all() failed: -22 Patch 1 rejects this at block-dirty-bitmap-add (and, wrapped in a transaction, denies the whole transaction). Patch 2 closes the same hole on the incoming-migration path. Patch 3 fixes a knock-on regression from patch 1's approach: a bitmap that was rejected from ever being written can still exist in memory read-only and must remain removable without requiring write access. v1 -> v2 * approach changed to deny rather than adopt (Vladimir) * added patch to add permission check on migration path * added patch to change permissions check on bitmap drop to more natural Signed-off-by: Denis V. Lunev <[email protected]> CC: Eric Blake <[email protected]> CC: Vladimir Sementsov-Ogievskiy <[email protected]> CC: John Snow <[email protected]> CC: Andrey Drobyshev <[email protected]> Denis V. Lunev (3): block/monitor: reject persistent bitmap add on a read-only node migration/block-dirty-bitmap: reject bitmap load onto ro node block/monitor: allow dropping a bitmap never stored on disk block/monitor/bitmap-qmp-cmds.c | 19 +++++++---- block/qcow2-bitmap.c | 9 +++++ migration/block-dirty-bitmap.c | 22 +++++++++---- qapi/block-core.json | 4 ++- tests/qemu-iotests/tests/migrate-bitmaps-test | 33 +++++++++++++++++++ .../tests/migrate-bitmaps-test.out | 4 +-- .../tests/remove-bitmap-from-backing | 29 +++++++++++++++- .../tests/remove-bitmap-from-backing.out | 22 ++++++++++++- 8 files changed, 124 insertions(+), 18 deletions(-) -- 2.53.0
