p2p: fix race causing dropped connections during sync

Without this commit:
1) read height from DB
2) add block to chain in separate thread
3) read chain for block id's and request them from peer
4) ERR in handle_response_chain_entry, peer's first block is the
one that was added to the chain, which has block idx=height from
step 1.

This commit reads the chain for height and highest block id's
in one go while holding the m_blockchain_lock to avoid the race.

4 files changed, 7 insertions, 6 deletions

diff --git a/src/cryptonote_core/blockchain.cpp b/src/cryptonote_core/blockchain.cpp
index a6c2e3faf..3a34089f5 100644
--- a/src/cryptonote_core/blockchain.cpp
+++ b/src/cryptonote_core/blockchain.cpp
@@ -728,13 +728,13 @@ crypto::hash Blockchain::get_tail_id() const
  *   powers of 2 less recent from there, so 13, 17, 25, etc...
  *
  */
-bool Blockchain::get_short_chain_history(std::list<crypto::hash>& ids) const
+bool Blockchain::get_short_chain_history(std::list<crypto::hash>& ids, uint64_t& current_height) const
 {
   LOG_PRINT_L3("Blockchain::" << __func__);
   CRITICAL_REGION_LOCAL(m_blockchain_lock);
   uint64_t i = 0;
   uint64_t current_multiplier = 1;
-  uint64_t sz = m_db->height();
+  uint64_t sz = current_height = m_db->height();
 
   if(!sz)
     return true;
diff --git a/src/cryptonote_core/blockchain.h b/src/cryptonote_core/blockchain.h
index f16bc7415..0fd81f4ba 100644
--- a/src/cryptonote_core/blockchain.h
+++ b/src/cryptonote_core/blockchain.h
@@ -445,10 +445,11 @@ namespace cryptonote
      *   powers of 2 less recent from there, so 13, 17, 25, etc...
      *
      * @param ids return-by-reference list to put the resulting hashes in
+     * @param current_height the current blockchain height, return-by-reference
      *
      * @return true
      */
-    bool get_short_chain_history(std::list<crypto::hash>& ids) const;
+    bool get_short_chain_history(std::list<crypto::hash>& ids, uint64_t& current_height) const;
 
     /**
      * @brief get recent block hashes for a foreign chain
diff --git a/src/cryptonote_core/cryptonote_core.cpp b/src/cryptonote_core/cryptonote_core.cpp
index 300fb2553..d30bc72a7 100644
--- a/src/cryptonote_core/cryptonote_core.cpp
+++ b/src/cryptonote_core/cryptonote_core.cpp
@@ -1536,9 +1536,9 @@ namespace cryptonote
     return m_mempool.get_pool_for_rpc(tx_infos, key_image_infos);
   }
   //-----------------------------------------------------------------------------------------------
-  bool core::get_short_chain_history(std::list<crypto::hash>& ids) const
+  bool core::get_short_chain_history(std::list<crypto::hash>& ids, uint64_t& current_height) const
   {
-    return m_blockchain_storage.get_short_chain_history(ids);
+    return m_blockchain_storage.get_short_chain_history(ids, current_height);
   }
   //-----------------------------------------------------------------------------------------------
   bool core::handle_get_objects(NOTIFY_REQUEST_GET_OBJECTS::request& arg, NOTIFY_RESPONSE_GET_OBJECTS::request& rsp, cryptonote_connection_context& context)
diff --git a/src/cryptonote_core/cryptonote_core.h b/src/cryptonote_core/cryptonote_core.h
index 362060b54..ab9a0ee12 100644
--- a/src/cryptonote_core/cryptonote_core.h
+++ b/src/cryptonote_core/cryptonote_core.h
@@ -580,7 +580,7 @@ namespace cryptonote
       *
       * @note see Blockchain::get_short_chain_history
       */
-     bool get_short_chain_history(std::list<crypto::hash>& ids) const;
+     bool get_short_chain_history(std::list<crypto::hash>& ids, uint64_t& current_height) const;
 
      /**
       * @copydoc Blockchain::find_blockchain_supplement(const std::list<crypto::hash>&, NOTIFY_RESPONSE_CHAIN_ENTRY::request&) const