Merge #19132: qt: lock cs_main, m_cached_tip_mutex in that order

f46b678acff0b2e75e26aa50b14d935b3d251a2a qt: lock cs_main, m_cached_tip_mutex in that order (Vasil Dimov)

Pull request description:

  Always lock the mutexes `cs_main` and `m_cached_tip_mutex` in
  the same order: `cs_main`, `m_cached_tip_mutex`. Otherwise we may end up
  in a deadlock.

  `ClientModel::m_cached_tip_blocks` is protected by
  `ClientModel::m_cached_tip_mutex`. There are two access paths that
  lock the two mutexes in opposite order:

  ```
  validation.cpp:2868 CChainState::ActivateBestChain(): lock cs_main
  validation.cpp:2916 CChainState::ActivateBestChain(): call uiInterface.NotifyBlockTip()
  ui_interface.cpp:52 CClientUIInterface::NotifyBlockTip(): go deep in boost
  ...
  qt/clientmodel.cpp:255 BlockTipChanged(): lock m_cached_tip_mutex
  ```

  and

  ```
  qt/clientmodel.cpp:119 ClientModel::getBestBlockHash(): lock m_cached_tip_mutex
  qt/clientmodel.cpp:121 ClientModel::getBestBlockHash(): call m_node.getBestBlockHash()
  interfaces/node.cpp:200 NodeImpl::getBestBlockHash(): lock cs_main
  ```

  From `debug.log`:

  ```
  POTENTIAL DEADLOCK DETECTED
  Previous lock order was:
   m_cs_chainstate validation.cpp:2851
   (1) cs_main validation.cpp:2868
   ::mempool.cs validation.cpp:2868
   (2) clientmodel->m_cached_tip_mutex qt/clientmodel.cpp:255
  Current lock order is:
   (2) m_cached_tip_mutex qt/clientmodel.cpp:119
   (1) ::cs_main interfaces/node.cpp:200
  ```

  The possible deadlock was introduced in #17993

ACKs for top commit:
  jonasschnelli:
    Tested ACK f46b678acff0b2e75e26aa50b14d935b3d251a2a

Tree-SHA512: 904f24b39bdc97c4d0ecb897a6980d8d479814535eb167e23105238800ea2f1f85273e3370cf894db58bc597f94c4f2e81fb68d0ff3362d468c16af5ce8f5d78

0 files changed, 0 insertions, 0 deletions