blockchain: detect and log bad difficulty calculations

src/cryptonote_core/blockchain.cpp

@@ -812,12 +812,20 @@ bool Blockchain::get_block_by_hash(const crypto::hash &h, block &blk, bool *orph
 // less blocks than desired if there aren't enough.
 difficulty_type Blockchain::get_difficulty_for_next_block()
 {
+  LOG_PRINT_L3("Blockchain::" << __func__);
+
+  std::stringstream ss;
+  bool print = false;
+
+  int done = 0;
+  ss << "get_difficulty_for_next_block: height " << m_db->height() << std::endl;
   if (m_fixed_difficulty)
   {
     return m_db->height() ? m_fixed_difficulty : 1;
   }
 
-  LOG_PRINT_L3("Blockchain::" << __func__);
+start:
+  difficulty_type D = 0;
 
   crypto::hash top_hash = get_tail_id();
   {
@@ -826,21 +834,30 @@ difficulty_type Blockchain::get_difficulty_for_next_block()
     // something a bit out of date, but that's fine since anything which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
+    ss << "Locked, tail id " << top_hash << ", cached is " << m_difficulty_for_next_block_top_hash << std::endl;
     if (top_hash == m_difficulty_for_next_block_top_hash)
-      return m_difficulty_for_next_block;
+    {
+      ss << "Same, using cached diff " << m_difficulty_for_next_block << std::endl;
+      D = m_difficulty_for_next_block;
+    }
   }
 
   CRITICAL_REGION_LOCAL(m_blockchain_lock);
   std::vector<uint64_t> timestamps;
   std::vector<difficulty_type> difficulties;
   uint64_t height;
-  top_hash = get_tail_id(height); // get it again now that we have the lock
+  auto new_top_hash = get_tail_id(height); // get it again now that we have the lock
-  ++height; // top block height to blockchain height
+  ++height;
+  if (!(new_top_hash == top_hash)) D=0;
+  ss << "Re-locked, height " << height << ", tail id " << new_top_hash << (new_top_hash == top_hash ? "" : " (different)") << std::endl;
+  top_hash = new_top_hash;
+
   // ND: Speedup
   // 1. Keep a list of the last 735 (or less) blocks that is used to compute difficulty,
   //    then when the next block difficulty is queried, push the latest height data and
   //    pop the oldest one from the list. This only requires 1x read per height instead
   //    of doing 735 (DIFFICULTY_BLOCKS_COUNT).
+  bool check = false;
   if (m_timestamps_and_difficulties_height != 0 && ((height - m_timestamps_and_difficulties_height) == 1) && m_timestamps.size() >= DIFFICULTY_BLOCKS_COUNT)
   {
     uint64_t index = height - 1;
@@ -855,8 +872,12 @@ difficulty_type Blockchain::get_difficulty_for_next_block()
     m_timestamps_and_difficulties_height = height;
     timestamps = m_timestamps;
     difficulties = m_difficulties;
+    check = true;
   }
-  else
+  //else
+  std::vector<uint64_t> timestamps_from_cache = timestamps;
+  std::vector<difficulty_type> difficulties_from_cache = difficulties;
+
   {
     uint64_t offset = height - std::min <uint64_t> (height, static_cast<uint64_t>(DIFFICULTY_BLOCKS_COUNT));
     if (offset == 0)
@@ -869,22 +890,68 @@ difficulty_type Blockchain::get_difficulty_for_next_block()
       timestamps.reserve(height - offset);
       difficulties.reserve(height - offset);
     }
+    ss << "Looking up " << (height - offset) << " from " << offset << std::endl;
     for (; offset < height; offset++)
     {
       timestamps.push_back(m_db->get_block_timestamp(offset));
       difficulties.push_back(m_db->get_block_cumulative_difficulty(offset));
     }
 
+    if (check) if (timestamps != timestamps_from_cache || difficulties !=difficulties_from_cache)
+    {
+      ss << "Inconsistency XXX:" << std::endl;
+      ss << "top hash: "<<top_hash << std::endl;
+      ss << "timestamps: " << timestamps_from_cache.size() << " from cache, but " << timestamps.size() << " without" << std::endl;
+      ss << "difficulties: " << difficulties_from_cache.size() << " from cache, but " << difficulties.size() << " without" << std::endl;
+      ss << "timestamps_from_cache:" << std::endl; for (const auto &v :timestamps_from_cache) ss << "  " << v << std::endl;
+      ss << "timestamps:" << std::endl; for (const auto &v :timestamps) ss << "  " << v << std::endl;
+      ss << "difficulties_from_cache:" << std::endl; for (const auto &v :difficulties_from_cache) ss << "  " << v << std::endl;
+      ss << "difficulties:" << std::endl; for (const auto &v :difficulties) ss << "  " << v << std::endl;
+
+      uint64_t dbh = m_db->height();
+      uint64_t sh = dbh < 10000 ? 0 : dbh - 10000;
+      ss << "History from -10k at :" << dbh << ", from " << sh << std::endl;
+      for (uint64_t h = sh; h < dbh; ++h)
+      {
+        uint64_t ts = m_db->get_block_timestamp(h);
+        difficulty_type d = m_db->get_block_cumulative_difficulty(h);
+        ss << "  " << h << " " << ts << " " << d << std::endl;
+      }
+      print = true;
+    }
     m_timestamps_and_difficulties_height = height;
     m_timestamps = timestamps;
     m_difficulties = difficulties;
   }
+
   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;
+  if (D && D != diff)
+  {
+    ss << "XXX Mismatch at " << height << "/" << top_hash << "/" << get_tail_id() << ": cached " << D << ", real " << diff << std::endl;
+    print = true;
+  }
+
+  ++done;
+  if (done == 1 && D && D != diff)
+  {
+    print = true;
+    ss << "Might be a race. Let's see what happens if we try again..." << std::endl;
+    epee::misc_utils::sleep_no_w(100);
+    goto start;
+  }
+  ss << "Diff for " << top_hash << ": " << diff << std::endl;
+  if (print)
+  {
+    MGINFO("START DUMP");
+    MGINFO(ss.str());
+    MGINFO("END DUMP");
+    MGINFO("Please send moneromooo on Freenode the contents of this log, from a couple dozen lines before START DUMP to END DUMP");
+  }
   return diff;
 }
 //------------------------------------------------------------------