fix(bug): crash on takeover and info replication (#3282)

Signed-off-by: adi_holden <adi@dragonflydb.io>

src/server/server_family.cc

@@ -2258,9 +2258,12 @@ void ServerFamily::Info(CmdArgList args, ConnectionContext* cntx) {
   }
 
   if (should_enter("REPLICATION")) {
-    ServerState& etl = *ServerState::tlocal();
-
-    if (etl.is_master) {
+    unique_lock lk(replicaof_mu_);
+    // Thread local var is_master is updated under mutex replicaof_mu_ together with replica_,
+    // ensuring eventual consistency of is_master. When determining if the server is a replica and
+    // accessing the replica_ object, we must lock replicaof_mu_. Using is_master alone is
+    // insufficient in this scenario.
+    if (!replica_) {
       append("role", "master");
       append("connected_slaves", m.facade_stats.conn_stats.num_replicas);
       const auto& replicas = m.replication_metrics;
@@ -2274,10 +2277,6 @@ void ServerFamily::Info(CmdArgList args, ConnectionContext* cntx) {
     } else {
       append("role", GetFlag(FLAGS_info_replication_valkey_compatible) ? "slave" : "replica");
 
-      // The replica pointer can still be mutated even while master=true,
-      // we don't want to drop the replica object in this fiber
-      unique_lock lk{replicaof_mu_};
-
       auto replication_info_cb = [&](Replica::Info rinfo) {
         append("master_host", rinfo.host);
         append("master_port", rinfo.port);
@@ -2737,8 +2736,12 @@ err:
 
 void ServerFamily::Role(CmdArgList args, ConnectionContext* cntx) {
   auto* rb = static_cast<RedisReplyBuilder*>(cntx->reply_builder());
-  ServerState& etl = *ServerState::tlocal();
-  if (etl.is_master) {
+  unique_lock lk(replicaof_mu_);
+  // Thread local var is_master is updated under mutex replicaof_mu_ together with replica_,
+  // ensuring eventual consistency of is_master. When determining if the server is a replica and
+  // accessing the replica_ object, we must lock replicaof_mu_. Using is_master alone is
+  // insufficient in this scenario.
+  if (!replica_) {
     rb->StartArray(2);
     rb->SendBulkString("master");
     auto vec = dfly_cmd_->GetReplicasRoleInfo();
@@ -2751,7 +2754,6 @@ void ServerFamily::Role(CmdArgList args, ConnectionContext* cntx) {
     }
 
   } else {
-    unique_lock lk{replicaof_mu_};
     rb->StartArray(4 + cluster_replicas_.size() * 3);
     rb->SendBulkString(GetFlag(FLAGS_info_replication_valkey_compatible) ? "slave" : "replica");
 

tests/dragonfly/instance.py

@@ -336,7 +336,7 @@ class DflyInstanceFactory:
         args.setdefault("noversion_check", None)
         # MacOs does not set it automatically, so we need to set it manually
         args.setdefault("maxmemory", "8G")
-        vmod = "dragonfly_connection=1,accept_server=1,listener_interface=1,main_service=1,rdb_save=1,replica=1,cluster_family=1"
+        vmod = "dragonfly_connection=1,accept_server=1,listener_interface=1,main_service=1,rdb_save=1,replica=1,cluster_family=1,dflycmd=1"
         args.setdefault("vmodule", vmod)
         args.setdefault("jsonpathv2")
 

tests/dragonfly/replication_test.py

@@ -1151,10 +1151,7 @@ take_over_cases = [
 @pytest.mark.parametrize("master_threads, replica_threads", take_over_cases)
 @pytest.mark.asyncio
 async def test_take_over_counters(df_factory, master_threads, replica_threads):
-    master = df_factory.create(
-        proactor_threads=master_threads,
-        logtostderr=True,
-    )
+    master = df_factory.create(proactor_threads=master_threads)
     replica1 = df_factory.create(proactor_threads=replica_threads)
     replica2 = df_factory.create(proactor_threads=replica_threads)
     replica3 = df_factory.create(proactor_threads=replica_threads)
@@ -1214,11 +1211,7 @@ async def test_take_over_seeder(
     request, df_factory, df_seeder_factory, master_threads, replica_threads
 ):
     tmp_file_name = "".join(random.choices(string.ascii_letters, k=10))
-    master = df_factory.create(
-        proactor_threads=master_threads,
-        dbfilename=f"dump_{tmp_file_name}",
-        logtostderr=True,
-    )
+    master = df_factory.create(proactor_threads=master_threads, dbfilename=f"dump_{tmp_file_name}")
     replica = df_factory.create(proactor_threads=replica_threads)
     df_factory.start_all([master, replica])
 
@@ -1229,17 +1222,27 @@ async def test_take_over_seeder(
     await c_replica.execute_command(f"REPLICAOF localhost {master.port}")
     await wait_available_async(c_replica)
 
-    async def seed():
-        await seeder.run(target_ops=3000)
+    fill_task = asyncio.create_task(seeder.run())
 
-    fill_task = asyncio.create_task(seed())
+    stop_info = False
+
+    async def info_task():
+        my_client = replica.client()
+        while not stop_info:
+            info = await my_client.info("replication")
+            asyncio.sleep(0.5)
+
+    info_task = asyncio.create_task(info_task())
 
     # Give the seeder a bit of time.
-    await asyncio.sleep(1)
+    await asyncio.sleep(3)
+    logging.debug("running repltakover")
     await c_replica.execute_command(f"REPLTAKEOVER 5 SAVE")
+    logging.debug("after running repltakover")
     seeder.stop()
 
     assert await c_replica.execute_command("role") == ["master", []]
+    stop_info = True
 
     # Need to wait a bit to give time to write the shutdown snapshot
     await asyncio.sleep(1)
@@ -1258,10 +1261,7 @@ async def test_take_over_seeder(
 @pytest.mark.parametrize("master_threads, replica_threads", [[4, 4]])
 @pytest.mark.asyncio
 async def test_take_over_read_commands(df_factory, master_threads, replica_threads):
-    master = df_factory.create(
-        proactor_threads=master_threads,
-        logtostderr=True,
-    )
+    master = df_factory.create(proactor_threads=master_threads)
     replica = df_factory.create(proactor_threads=replica_threads)
     df_factory.start_all([master, replica])