The problem is that when dsl_bookmark_destroy_check() is executed from open
context (the pre-check), it fills in dbda_success based on the existence of the
bookmark.
But the bookmark (or containing filesystem as in this case) can be destroyed
before we get to syncing context. When we re-run dsl_bookmark_destroy_check()
in syncing
context, it will not add the deleted bookmark to dbda_success, intending for
dsl_bookmark_destroy_sync() to not process it. But because the bookmark is
still in dbda_success
from the open-context call, we do try to destroy it.
The fix is that dsl_bookmark_destroy_check() should not modify dbda_success
when called from open context.