fix: avoid lock order inversion between cs_main and cs_quorumBaseBloc…

…kIndexCache

src/llmq/quorums.cpp

@@ -636,11 +636,13 @@ CQuorumCPtr CQuorumManager::GetQuorum(Consensus::LLMQType llmqType, const uint25
 {
     const CBlockIndex* pQuorumBaseBlockIndex = [&]() {
         // Lock contention may still be high here; consider using a shared lock
-        LOCK(cs_quorumBaseBlockIndexCache);
+        // We cannot hold cs_quorumBaseBlockIndexCache the whole time as that creates lock-order inversion with cs_main;
+        // We cannot aquire cs_main if we have cs_quorumBaseBlockIndexCache held
         const CBlockIndex* pindex;
-        if (!quorumBaseBlockIndexCache.get(quorumHash, pindex)) {
+        if (!WITH_LOCK(cs_quorumBaseBlockIndexCache, return quorumBaseBlockIndexCache.get(quorumHash, pindex))) {
             pindex = WITH_LOCK(cs_main, return m_chainstate.m_blockman.LookupBlockIndex(quorumHash));
             if (pindex) {
+                LOCK(cs_quorumBaseBlockIndexCache);
                 quorumBaseBlockIndexCache.insert(quorumHash, pindex);
             }
         }