From c5b47389df8fab10afd1582b8363524fb23b668f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Markus=20M=C3=A4kel=C3=A4?= <markus.makela@mariadb.com>
Date: Fri, 21 Aug 2020 08:27:34 +0300
Subject: [PATCH] MXS-3106: Always write the final COM_QUIT

This seems to help with a regression that was introduced in 2.4.11.
---
 include/maxscale/dcb.hh                            |  5 +++++
 include/maxscale/protocol/mysql.hh                 |  1 -
 server/core/dcb.cc                                 |  5 +++--
 .../protocol/MySQL/mariadbbackend/mysql_backend.cc | 14 +++-----------
 server/modules/protocol/MySQL/mysql_common.cc      |  1 -
 5 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/include/maxscale/dcb.hh b/include/maxscale/dcb.hh
index 8dc9659f6..dc0c6b977 100644
--- a/include/maxscale/dcb.hh
+++ b/include/maxscale/dcb.hh
@@ -206,6 +206,11 @@ struct DCB : public MXB_POLL_DATA
     bool           high_water_reached = false;  /** High water mark reached, to determine whether we need to
                                                  * release
                                                  * throttle */
+
+    // Enable this to prevent write errors from being logged. Helps reduce false errors when writes to
+    // potentially closed DCBs are done.
+    bool silence_write_errors = false;
+
     struct
     {
         DCB* next = nullptr;        /**< Next DCB in owning thread's list */
diff --git a/include/maxscale/protocol/mysql.hh b/include/maxscale/protocol/mysql.hh
index 78c878dc2..3af98719d 100644
--- a/include/maxscale/protocol/mysql.hh
+++ b/include/maxscale/protocol/mysql.hh
@@ -340,7 +340,6 @@ typedef struct
     bool                   collect_result;              /*< Collect the next result set as one buffer */
     bool                   changing_user;
     bool                   track_state;     /*< Track session state */
-    bool                   send_com_quit;
     uint32_t               num_eof_packets; /*< Encountered eof packet number, used for check
                                              * packet type */
     bool large_query;                       /*< Whether to ignore the command byte of the next
diff --git a/server/core/dcb.cc b/server/core/dcb.cc
index aa03b9660..f9dc3f1b3 100644
--- a/server/core/dcb.cc
+++ b/server/core/dcb.cc
@@ -822,7 +822,7 @@ static int dcb_log_errors_SSL(DCB* dcb, int ret)
     unsigned long ssl_errno;
 
     ssl_errno = ERR_get_error();
-    if (0 == ssl_errno)
+    if (0 == ssl_errno || dcb->silence_write_errors)
     {
         return 0;
     }
@@ -1806,7 +1806,8 @@ static int gw_write(DCB* dcb, GWBUF* writeq, bool* stop_writing)
     if (written < 0)
     {
         *stop_writing = true;
-        if (saved_errno != EAGAIN && saved_errno != EWOULDBLOCK && saved_errno != EPIPE)
+        if (saved_errno != EAGAIN && saved_errno != EWOULDBLOCK && saved_errno != EPIPE
+            && !dcb->silence_write_errors)
         {
             MXS_ERROR("Write to %s %s in state %s failed: %d, %s",
                       dcb->type(),
diff --git a/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc b/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc
index 40019d170..020fc2a63 100644
--- a/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc
+++ b/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc
@@ -1291,12 +1291,6 @@ static int gw_MySQLWrite_backend(DCB* dcb, GWBUF* queue)
             }
             else
             {
-
-                if (cmd == MXS_COM_QUIT)
-                {
-                    backend_protocol->send_com_quit = false;
-                }
-
                 if (GWBUF_IS_IGNORABLE(queue))
                 {
                     /** The response to this command should be ignored */
@@ -1409,11 +1403,9 @@ static int gw_backend_close(DCB* dcb)
     mxb_assert(dcb->session || dcb->persistentstart);
     MySQLProtocol* proto = (MySQLProtocol*)dcb->protocol;
 
-    if (proto->send_com_quit && proto->protocol_auth_state == MXS_AUTH_STATE_COMPLETE)
-    {
-        // Send a COM_QUIT to the backend being closed, we haven't routed one to it yet.
-        dcb_write(dcb, mysql_create_com_quit(NULL, 0));
-    }
+    // Always send a COM_QUIT to the backend being closed. This causes the connection to be closed faster.
+    dcb->silence_write_errors = true;
+    dcb_write(dcb, mysql_create_com_quit(NULL, 0));
 
     /** Free protocol data */
     mysql_protocol_done(dcb);
diff --git a/server/modules/protocol/MySQL/mysql_common.cc b/server/modules/protocol/MySQL/mysql_common.cc
index 547f3c869..2c5f7ccd0 100644
--- a/server/modules/protocol/MySQL/mysql_common.cc
+++ b/server/modules/protocol/MySQL/mysql_common.cc
@@ -64,7 +64,6 @@ MySQLProtocol* mysql_protocol_init(DCB* dcb, int fd)
     p->num_eof_packets = 0;
     p->large_query = false;
     p->track_state = false;
-    p->send_com_quit = true;
     /*< Assign fd with protocol */
     p->fd = fd;
     p->owner_dcb = dcb;