block/qcow2-bitmap: fix crash bug in qcow2_co_remove_persistent_dirty_bitmap
Here is double bug:
First, return error but not set errp. This may lead to:
qmp block-dirty-bitmap-remove may report success when actually failed
block-dirty-bitmap-remove used in a transaction will crash, as
qmp_transaction will think that it returned success and will call
block_dirty_bitmap_remove_commit which will crash, as state->bitmap is
NULL
Second (like in anecdote), this case is not an error at all. As it is
documented in the comment above bdrv_co_remove_persistent_dirty_bitmap
definition, absence of bitmap is not an error, and similar case handled
at start of qcow2_co_remove_persistent_dirty_bitmap, it returns 0 when
there is no bitmaps at all.
But when there are some bitmaps, but not the requested one, it return
error with errp unset.
Fix that.
Trigger:
1. create persistent bitmap A
2. shutdown vm (bitmap A is synced)
3. start vm
4. create persistent bitmap B
5. remove bitmap B - it fails (and crashes if in transaction)
Potential workaround (rather invasive to ask clients to implement it):
1. create persistent bitmap A
2. shutdown vm
3. start vm
4. create persistent bitmap B
5. remember, that we want to remove bitmap B after vm shutdown
...
some other operations
...
6. vm shutdown
7. start vm in stopped mode, and remove all bitmaps marked for removing
8. stop vm
Fixes: b56a1e31759b750
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20191205193049.30666-1-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
[eblake: commit message tweaks]
Signed-off-by: Eric Blake <eblake@redhat.com>
1 file changed
