@charles: It's a stack overflow involving inifinite recursion with
virtual_libraries_for_books. Here's the trace:

Fatal Python error: _Py_CheckRecursiveCall: Cannot recover from stack overflow.
Python runtime state: initialized

Thread 0x00007fb6f37fe640 (most recent call first):
  File "/usr/lib/python3.9/threading.py", line 316 in wait
  File "/usr/lib/python3.9/threading.py", line 574 in wait
  File "/home/kovid/work/calibre/src/calibre/db/backup.py", line 47 in wait
  File "/home/kovid/work/calibre/src/calibre/db/backup.py", line 53 in run
  File "/usr/lib/python3.9/threading.py", line 954 in _bootstrap_inner
  File "/usr/lib/python3.9/threading.py", line 912 in _bootstrap

Thread 0x00007fb6f3fff640 (most recent call first):
  File "/usr/lib/python3.9/socket.py", line 831 in create_connection
  File "/usr/lib/python3.9/http/client.py", line 919 in connect
  File "/usr/lib/python3.9/http/client.py", line 1415 in connect
  File "/home/kovid/work/calibre/src/calibre/utils/https.py", line 195 in get_https_resource_securely
  File "/home/kovid/work/calibre/src/calibre/gui2/update.py", line 49 in get_newest_version
  File "/home/kovid/work/calibre/src/calibre/gui2/update.py", line 89 in run
  File "/usr/lib/python3.9/threading.py", line 954 in _bootstrap_inner
  File "/usr/lib/python3.9/threading.py", line 912 in _bootstrap

Thread 0x00007fb711079640 (most recent call first):
  File "/home/kovid/work/calibre/src/calibre/gui2/device.py", line 432 in run
  File "/usr/lib/python3.9/threading.py", line 954 in _bootstrap_inner
  File "/usr/lib/python3.9/threading.py", line 912 in _bootstrap

Thread 0x00007fb7118ba640 (most recent call first):
  File "/usr/lib/python3.9/threading.py", line 316 in wait
  File "/usr/lib/python3.9/queue.py", line 180 in get
  File "/home/kovid/work/calibre/src/calibre/utils/ipc/server.py", line 167 in run
  File "/usr/lib/python3.9/threading.py", line 954 in _bootstrap_inner
  File "/usr/lib/python3.9/threading.py", line 912 in _bootstrap

Current thread 0x00007fb74e1e9740 (most recent call first):
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 506 in get_matches
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 453 in _get_matches
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 449 in evaluate_token
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 406 in evaluate_and
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 392 in _parse
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 448 in evaluate_token
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 413 in evaluate_or
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 392 in _parse
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 448 in evaluate_token
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 413 in evaluate_or
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 414 in evaluate_or
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 392 in _parse
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 448 in evaluate_token
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 392 in _parse
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 365 in parse
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 496 in parse
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 994 in _do_search
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 932 in __call__
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 1086 in search
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 2219 in virtual_libraries_for_books
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 72 in call_func_with_lock
  File "/home/kovid/work/calibre/src/calibre/db/view.py", line 236 in get_virtual_libraries_for_books
  File "/home/kovid/work/calibre/src/calibre/utils/formatter_functions.py", line 1718 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/formatter_functions.py", line 136 in eval_
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 811 in do_node_func
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1131 in expr
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 718 in expression_list
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 704 in program
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1234 in _eval_program
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1326 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1367 in safe_format
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 280 in __render_composite
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 312 in get_value_with_cache
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 326 in iter_searchable_values
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 755 in get_matches
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 453 in _get_matches
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 449 in evaluate_token
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 392 in _parse
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 365 in parse
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 496 in parse
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 994 in _do_search
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 932 in __call__
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 1086 in search
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 2219 in virtual_libraries_for_books
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 72 in call_func_with_lock
  File "/home/kovid/work/calibre/src/calibre/db/view.py", line 236 in get_virtual_libraries_for_books
  File "/home/kovid/work/calibre/src/calibre/utils/formatter_functions.py", line 1718 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/formatter_functions.py", line 136 in eval_
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 811 in do_node_func
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1131 in expr
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 718 in expression_list
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 704 in program
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1234 in _eval_program
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1326 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1367 in safe_format
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 280 in __render_composite
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 312 in get_value_with_cache
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 326 in iter_searchable_values
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 755 in get_matches
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 453 in _get_matches
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 449 in evaluate_token
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 392 in _parse
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 365 in parse
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 496 in parse
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 994 in _do_search
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 932 in __call__
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 1086 in search
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 2219 in virtual_libraries_for_books
  File "/home/kovid/work/calibre/src/calibre/db/cache.py", line 72 in call_func_with_lock
  File "/home/kovid/work/calibre/src/calibre/db/view.py", line 236 in get_virtual_libraries_for_books
  File "/home/kovid/work/calibre/src/calibre/utils/formatter_functions.py", line 1718 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/formatter_functions.py", line 136 in eval_
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 811 in do_node_func
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1131 in expr
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 718 in expression_list
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 704 in program
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1234 in _eval_program
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1326 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/formatter.py", line 1367 in safe_format
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 280 in __render_composite
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 312 in get_value_with_cache
  File "/home/kovid/work/calibre/src/calibre/db/fields.py", line 326 in iter_searchable_values
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 755 in get_matches
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 453 in _get_matches
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 449 in evaluate_token
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 400 in evaluate
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 392 in _parse
  File "/home/kovid/work/calibre/src/calibre/utils/search_query_parser.py", line 365 in parse
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 496 in parse
  File "/home/kovid/work/calibre/src/calibre/db/search.py", line 994 in _do_search
  ...