From f97f422379c6b0fe6f5bec130a0ea80b522ed382 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20M=C3=A4kel=C3=A4?= <markus.makela@mariadb.com>
Date: Tue, 26 Jun 2018 12:45:08 +0300
Subject: [PATCH] Don't use closed backends

Only use backends that are still in use. The COM_STMT_EXECUTE and
COM_STMT_FETCH relationship caused unused backends to be used.
---
 server/core/backend.cc                               |  3 +++
 .../routing/readwritesplit/rwsplit_route_stmt.cc     | 12 ++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/server/core/backend.cc b/server/core/backend.cc
index 0a6f631d0..967f06130 100644
--- a/server/core/backend.cc
+++ b/server/core/backend.cc
@@ -196,6 +196,7 @@ bool Backend::connect(MXS_SESSION* session)
 
 bool Backend::write(GWBUF* buffer, response_type type)
 {
+    ss_dassert(in_use());
     bool rval = m_dcb->func.write(m_dcb, buffer) != 0;
 
     if (rval && type == EXPECT_RESPONSE)
@@ -208,6 +209,7 @@ bool Backend::write(GWBUF* buffer, response_type type)
 
 bool Backend::auth(GWBUF* buffer)
 {
+    ss_dassert(in_use());
     bool rval = false;
 
     if (m_dcb->func.auth(m_dcb, NULL, m_dcb->session, buffer) == 1)
@@ -232,6 +234,7 @@ void Backend::store_command(GWBUF* buffer)
 
 bool Backend::write_stored_command()
 {
+    ss_dassert(in_use());
     bool rval = false;
 
     if (m_pending_cmd.length())
diff --git a/server/modules/routing/readwritesplit/rwsplit_route_stmt.cc b/server/modules/routing/readwritesplit/rwsplit_route_stmt.cc
index 75e2cdc81..649d76e86 100644
--- a/server/modules/routing/readwritesplit/rwsplit_route_stmt.cc
+++ b/server/modules/routing/readwritesplit/rwsplit_route_stmt.cc
@@ -999,8 +999,15 @@ SRWBackend handle_slave_is_target(RWSplit *inst, RWSplitSession *rses,
 
         if (it != rses->exec_map.end())
         {
-            target = it->second;
-            MXS_INFO("COM_STMT_FETCH on %s", target->uri());
+            if (it->second->in_use())
+            {
+                target = it->second;
+                MXS_INFO("COM_STMT_FETCH on %s", target->uri());
+            }
+            else
+            {
+                MXS_INFO("Old target not in use, cannot proceed");
+            }
         }
         else
         {
@@ -1016,6 +1023,7 @@ SRWBackend handle_slave_is_target(RWSplit *inst, RWSplitSession *rses,
     if (target)
     {
         atomic_add_uint64(&inst->stats().n_slave, 1);
+        ss_dassert(target->in_use());
     }
     else
     {