MDEV-28561 Assertion failed: !pfs->m_idle || (state == PSI_SOCKET_STATE_ACTIVE)

The error was specific to threadpool/compressed protocol.
set_thd_idle() set socket state to idle twice, causing assert failure.

This happens if unread compressed data on connection,after query was
finished. On a protocol level, this means a single compression packet
contains multiple command packets.

sql/threadpool_common.cc

@@ -124,12 +124,17 @@ static void re_init_net_server_extension(THD *thd)
 
 #endif /* HAVE_PSI_INTERFACE */
 
+static inline bool has_unread_compressed_data(const NET *net)
+{
+  return net->compress && net->remain_in_buf;
+}
 
 static inline void set_thd_idle(THD *thd)
 {
   thd->net.reading_or_writing= 1;
 #ifdef HAVE_PSI_INTERFACE
-  net_before_header_psi(&thd->net, thd, 0);
+  if (!has_unread_compressed_data(&thd->net))
+    net_before_header_psi(&thd->net, thd, 0);
 #endif
 }
 
@@ -326,10 +331,8 @@ static void handle_wait_timeout(THD *thd)
 static bool has_unread_data(THD* thd)
 {
   NET *net= &thd->net;
-  if (net->compress && net->remain_in_buf)
-    return true;
   Vio *vio= net->vio;
-  return vio->has_data(vio);
+  return vio->has_data(vio) || has_unread_compressed_data(net);
 }
 
 

tests/mysql_client_test.c

@@ -20040,8 +20040,10 @@ static void test_bug17512527()
 static void test_compressed_protocol()
 {
   MYSQL *mysql_local;
+  MYSQL_STMT *stmt;
   char query[4096], *end;
   int i;
+  int rc;
   myheader("test_compressed_protocol");
 
   if (!(mysql_local= mysql_client_init(NULL)))
@@ -20064,14 +20066,34 @@ static void test_compressed_protocol()
   for (i=0 ; i < 2 ; i++)
   {
     MYSQL_RES *res;
-
-    int rc= mysql_real_query(mysql, query, (int) (end-query));
+    rc= mysql_real_query(mysql, query, (int) (end-query));
     myquery(rc);
     res= mysql_store_result(mysql);
     DBUG_ASSERT(res != 0);
     mysql_free_result(res);
   }
 
+  /*
+    Special compression protocol feature - it can pack
+    multiple protocol commands inside the same compression packet.
+
+    mariadbclient does it when MYSQL_STMT is reused in multiple
+    mysql_stmt_prepare() calls. It sends then COM_STMT_CLOSE and
+    COM_STMT_PREPARE together in a single compression packet.
+
+    Let's test, how server can handle that. There can be bugs
+    (MDEV-28561)
+  */
+  stmt= mysql_stmt_init(mysql_local);
+  check_stmt(stmt);
+  for (i= 0; i < 2; i++)
+  {
+    rc= mysql_stmt_prepare(stmt, "DO 1", -1);
+    myquery(rc);
+  }
+  rc= mysql_stmt_close(stmt);
+  myquery(rc);
+
   mysql_close(mysql_local);
 }