Fix per-hour user connection limits by making sure that the number of

connections is actually reset after an hour, and also fix (unlikely)
conditions under which the per-hour query and connection limits could be
exceeded. (Bug #8350)


sql/sql_parse.cc:
  Add time_out_user_resource_limits() function to
  reset the user resource limits before they are
  checked, and add locking to check_mqh() because
  not doing so isn't as safe as the old comment
  explaining its absence said it is.

sql/sql_parse.cc

@@ -52,7 +52,8 @@ extern "C" pthread_mutex_t THR_LOCK_keycache;
 extern "C" int gethostname(char *name, int namelen);
 #endif
 
-static int check_for_max_user_connections(USER_CONN *uc);
+static void time_out_user_resource_limits(THD *thd, USER_CONN *uc);
+static int check_for_max_user_connections(THD *thd, USER_CONN *uc);
 static void decrease_user_connections(USER_CONN *uc);
 static bool check_db_used(THD *thd,TABLE_LIST *tables);
 static bool check_merge_table_access(THD *thd, char *db, TABLE_LIST *tables);
@@ -272,7 +273,7 @@ static bool check_user(THD *thd,enum_server_command command, const char *user,
     return -1;
   if (thd->user_connect && (thd->user_connect->user_resources.connections ||
 			    max_user_connections) &&
-      check_for_max_user_connections(thd->user_connect))
+      check_for_max_user_connections(thd, thd->user_connect))
     return -1;
   if (db && db[0])
   {
@@ -312,7 +313,7 @@ void init_max_user_conn(void)
 }
 
 
-static int check_for_max_user_connections(USER_CONN *uc)
+static int check_for_max_user_connections(THD *thd, USER_CONN *uc)
 {
   int error=0;
   DBUG_ENTER("check_for_max_user_connections");
@@ -325,6 +326,7 @@ static int check_for_max_user_connections(USER_CONN *uc)
     error=1;
     goto end;
   }
+  time_out_user_resource_limits(thd, uc);
   if (uc->user_resources.connections &&
       uc->user_resources.connections <= uc->conn_per_hour)
   {
@@ -397,33 +399,54 @@ void init_update_queries(void)
 
 
 /*
-  Check if maximum queries per hour limit has been reached
-  returns 0 if OK.
+  Reset per-hour user resource limits when it has been more than
+  an hour since they were last checked
 
-  In theory we would need a mutex in the USER_CONN structure for this to
-  be 100 % safe, but as the worst scenario is that we would miss counting
-  a couple of queries, this isn't critical.
-*/
+  SYNOPSIS:
+    time_out_user_resource_limits()
+    thd			Thread handler
+    uc			User connection details
 
+  NOTE:
+    This assumes that the LOCK_user_conn mutex has been acquired, so it is
+    safe to test and modify members of the USER_CONN structure.
+*/
 
-static bool check_mqh(THD *thd, uint check_command)
+void time_out_user_resource_limits(THD *thd, USER_CONN *uc)
 {
-  bool error=0;
   time_t check_time = thd->start_time ?  thd->start_time : time(NULL);
-  USER_CONN *uc=thd->user_connect;
-  DBUG_ENTER("check_mqh");
-  DBUG_ASSERT(uc != 0);
+  DBUG_ENTER("time_out_user_resource_limits");
 
   /* If more than a hour since last check, reset resource checking */
   if (check_time  - uc->intime >= 3600)
   {
-    (void) pthread_mutex_lock(&LOCK_user_conn);
     uc->questions=1;
     uc->updates=0;
     uc->conn_per_hour=0;
     uc->intime=check_time;
-    (void) pthread_mutex_unlock(&LOCK_user_conn);
   }
+
+  DBUG_VOID_RETURN;
+}
+
+
+/*
+  Check if maximum queries per hour limit has been reached
+  returns 0 if OK.
+*/
+
+static bool check_mqh(THD *thd, uint check_command)
+{
+  bool error=0;
+  time_t check_time = thd->start_time ?  thd->start_time : time(NULL);
+  USER_CONN *uc=thd->user_connect;
+  DBUG_ENTER("check_mqh");
+  DBUG_ASSERT(uc != 0);
+
+  (void) pthread_mutex_lock(&LOCK_user_conn);
+
+  time_out_user_resource_limits(thd, uc);
+
   /* Check that we have not done too many questions / hour */
   if (uc->user_resources.questions &&
       uc->questions++ >= uc->user_resources.questions)
@@ -446,6 +469,7 @@ static bool check_mqh(THD *thd, uint check_command)
     }
   }
 end:
+  (void) pthread_mutex_unlock(&LOCK_user_conn);
   DBUG_RETURN(error);
 }