Merge pull request #3940

f24cbc5 blockchain: fix deadlock with the difficulty cache (moneromooo-monero)

src/cryptonote_core/blockchain.cpp

@@ -807,16 +807,18 @@ difficulty_type Blockchain::get_difficulty_for_next_block()
 {
   LOG_PRINT_L3("Blockchain::" << __func__);
 
-  CRITICAL_REGION_LOCAL(m_difficulty_lock);
-  // we can call this without the blockchain lock, it might just give us
-  // something a bit out of date, but that's fine since anything which
-  // requires the blockchain lock will have acquired it in the first place,
-  // and it will be unlocked only when called from the getinfo RPC
   crypto::hash top_hash = get_tail_id();
-  if (top_hash == m_difficulty_for_next_block_top_hash)
-    return m_difficulty_for_next_block;
+  {
+    CRITICAL_REGION_LOCAL(m_difficulty_lock);
+    // we can call this without the blockchain lock, it might just give us
+    // something a bit out of date, but that's fine since anything which
+    // requires the blockchain lock will have acquired it in the first place,
+    // and it will be unlocked only when called from the getinfo RPC
+    if (top_hash == m_difficulty_for_next_block_top_hash)
+      return m_difficulty_for_next_block;
+  }
 
-  CRITICAL_REGION_LOCAL1(m_blockchain_lock);
+  CRITICAL_REGION_LOCAL(m_blockchain_lock);
   std::vector<uint64_t> timestamps;
   std::vector<difficulty_type> difficulties;
   auto height = m_db->height();
@@ -860,6 +862,8 @@ difficulty_type Blockchain::get_difficulty_for_next_block()
   }
   size_t target = get_difficulty_target();
   difficulty_type diff = next_difficulty(timestamps, difficulties, target);
+
+  CRITICAL_REGION_LOCAL1(m_difficulty_lock);
   m_difficulty_for_next_block_top_hash = top_hash;
   m_difficulty_for_next_block = diff;
   return diff;