Bug#18903155: BACKPORT BUG-18008907 TO 5.5+ VERSIONS.

Backporting patch committed for bug 18008907 to 5.5
and 5.6.

mysql-test/r/plugin.result

@@ -143,3 +143,73 @@ SELECT @@SESSION.example_double_thdvar;
 @@SESSION.example_double_thdvar
 1000.500000
 UNINSTALL PLUGIN example;
+#
+# BUG#18008907 - DEADLOCK BETWEEN MYSQL_CHANGE_USER(), SHOW VARIABLES AND INSTALL PLUGIN
+#
+CREATE PROCEDURE p_install()
+BEGIN
+INSTALL PLUGIN no_such_plugin SONAME 'no_such_object';
+END
+|
+CREATE PROCEDURE p_show_vars()
+BEGIN
+SELECT COUNT(*) FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES;
+END|
+connect con1, localhost, root,,;
+# Case 18008907_1: Deadlock situation cause by
+#                  con1: has LOCK_system_variables_hash and waits on LOCK_plugin  AND
+#                  default: has LOCK_plugin and waits on LOCK_system_variables_hash.
+#
+SET DEBUG_SYNC='acquired_LOCK_system_variables_hash SIGNAL install_plugin WAIT_FOR cont_show_vars';
+call p_show_vars();;
+connection default;
+SET DEBUG_SYNC='now WAIT_FOR install_plugin';
+SET DEBUG_SYNC='acquired_LOCK_plugin SIGNAL cont_show_vars';
+call p_install();;
+connection con1;
+COUNT(*)
+#
+SET DEBUG_SYNC='RESET';
+connection default;
+ERROR HY000: Can't open shared library
+SET DEBUG_SYNC='RESET';
+# Case 18008907_2: Deadlock situation caused by
+#                  default: has LOCK_system_variables_hash and waits on LOCK_global_system_variables,
+#                  con1: has LOCK_plugin and waits on LOCK_system_variables_hash AND
+#                  con2: has LOCK_global_system_variables and waits on LOCK_plugin.
+SET DEBUG_SYNC='acquired_LOCK_system_variables_hash SIGNAL install_plugin WAIT_FOR nothing TIMEOUT 10';
+call p_show_vars();;
+connection con1;
+SET DEBUG_SYNC='now WAIT_FOR install_plugin';
+SET DEBUG_SYNC='acquired_LOCK_plugin SIGNAL create_connection WAIT_FOR nothing TIMEOUT 10';
+call p_install();;
+connect con2, localhost, root,,;
+SET DEBUG_SYNC='now WAIT_FOR create_connection';
+connection con1;
+ERROR HY000: Can't open shared library
+connection default;
+COUNT(*)
+#
+Warnings:
+#	1639	debug sync point wait timed out
+disconnect con2;
+# Case 18008907_3: Testing Concurrent "Show Variables" and "Plugin Uninstall" operations.
+INSTALL PLUGIN example SONAME 'ha_example.so';
+connection con1;
+SET DEBUG_SYNC='acquired_LOCK_system_variables_hash SIGNAL uninstall_plugin WAIT_FOR go';
+call p_show_vars();;
+connect con2, localhost, root,,;
+SET DEBUG_SYNC='now WAIT_FOR uninstall_plugin';
+UNINSTALL PLUGIN example;;
+connection default;
+SET DEBUG_SYNC='now SIGNAL go';
+connection con1;
+COUNT(*)
+#
+connection con2;
+connection default;
+DROP PROCEDURE p_show_vars;
+DROP PROCEDURE p_install;
+SET DEBUG_SYNC='RESET';
+disconnect con1;
+disconnect con2;

mysql-test/t/plugin.test

+#
 --source include/not_windows_embedded.inc
 --source include/have_example_plugin.inc
+--source include/have_debug_sync.inc
 
 CREATE TABLE t1(a int) ENGINE=EXAMPLE;
 DROP TABLE t1;
@@ -137,3 +139,118 @@ SET SESSION example_double_thdvar = 1000.51;
 SELECT @@SESSION.example_double_thdvar;
 
 UNINSTALL PLUGIN example;
+
+--echo #
+--echo # BUG#18008907 - DEADLOCK BETWEEN MYSQL_CHANGE_USER(), SHOW VARIABLES AND INSTALL PLUGIN
+--echo #
+
+--enable_connect_log
+
+delimiter |;
+
+CREATE PROCEDURE p_install()
+BEGIN
+  INSTALL PLUGIN no_such_plugin SONAME 'no_such_object';
+END
+|
+
+CREATE PROCEDURE p_show_vars()
+BEGIN
+  SELECT COUNT(*) FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES;
+END|
+
+delimiter ;|
+
+connect(con1, localhost, root,,);
+
+--echo # Case 18008907_1: Deadlock situation cause by
+--echo #                  con1: has LOCK_system_variables_hash and waits on LOCK_plugin  AND
+--echo #                  default: has LOCK_plugin and waits on LOCK_system_variables_hash.
+--echo #
+SET DEBUG_SYNC='acquired_LOCK_system_variables_hash SIGNAL install_plugin WAIT_FOR cont_show_vars';
+--send call p_show_vars();
+
+connection default;
+SET DEBUG_SYNC='now WAIT_FOR install_plugin';
+SET DEBUG_SYNC='acquired_LOCK_plugin SIGNAL cont_show_vars';
+--send call p_install();
+
+connection con1;
+# Without fix, reap will hang.
+--replace_column 1 #
+--reap;
+SET DEBUG_SYNC='RESET';
+
+connection default;
+--replace_regex /(Can\'t open shared library).*$/\1/
+--error ER_CANT_OPEN_LIBRARY
+--reap;
+SET DEBUG_SYNC='RESET';
+
+--echo # Case 18008907_2: Deadlock situation caused by
+--echo #                  default: has LOCK_system_variables_hash and waits on LOCK_global_system_variables,
+--echo #                  con1: has LOCK_plugin and waits on LOCK_system_variables_hash AND
+--echo #                  con2: has LOCK_global_system_variables and waits on LOCK_plugin.
+
+SET DEBUG_SYNC='acquired_LOCK_system_variables_hash SIGNAL install_plugin WAIT_FOR nothing TIMEOUT 10';
+--send call p_show_vars();
+
+connection con1;
+SET DEBUG_SYNC='now WAIT_FOR install_plugin';
+SET DEBUG_SYNC='acquired_LOCK_plugin SIGNAL create_connection WAIT_FOR nothing TIMEOUT 10';
+--send call p_install();
+
+connect(con2, localhost, root,,);
+SET DEBUG_SYNC='now WAIT_FOR create_connection';
+# Without fix, deadlock situation will occur on timeout of debug_syncs in
+# default and con1.  Because of this, change_user operation hangs.
+change_user;
+
+connection con1;
+--replace_regex /(Can\'t open shared library).*$/\1/
+--error ER_CANT_OPEN_LIBRARY
+--reap;
+
+connection default;
+--replace_column 1 #
+--reap;
+disconnect con2;
+
+--echo # Case 18008907_3: Testing Concurrent "Show Variables" and "Plugin Uninstall" operations.
+
+#Installing plugin
+--replace_regex /\.dll/.so/
+eval INSTALL PLUGIN example SONAME '$EXAMPLE_PLUGIN';
+
+connection con1;
+#Acquiring LOCK_system_variables_hash and LOCK_plugin_delete
+SET DEBUG_SYNC='acquired_LOCK_system_variables_hash SIGNAL uninstall_plugin WAIT_FOR go';
+--send call p_show_vars();
+
+connect(con2, localhost, root,,);
+SET DEBUG_SYNC='now WAIT_FOR uninstall_plugin';
+--send UNINSTALL PLUGIN example;
+
+connection default;
+#Plugin Uninstall operation will wait until show variables operations releases LOCK_plugin_delete.
+let $wait_condition= SELECT count(*) = 1 FROM INFORMATION_SCHEMA.PROCESSLIST
+                     WHERE INFO LIKE 'UNINSTALL PLUGIN example' and
+                     STATE LIKE 'Waiting on cond';
+--source include/wait_condition.inc
+SET DEBUG_SYNC='now SIGNAL go';
+
+connection con1;
+--replace_column 1 #
+--reap
+
+connection con2;
+--reap
+
+connection default;
+DROP PROCEDURE p_show_vars;
+DROP PROCEDURE p_install;
+SET DEBUG_SYNC='RESET';
+disconnect con1;
+disconnect con2;
+
+--disable_connect_log

sql/sql_plugin.cc

@@ -33,6 +33,7 @@
 #include "sql_audit.h"
 #include <mysql/plugin_auth.h>
 #include "lock.h"                               // MYSQL_LOCK_IGNORE_TIMEOUT
+#include "debug_sync.h"
 #define REPORT_TO_LOG  1
 #define REPORT_TO_USER 2
 
@@ -131,6 +132,12 @@ static int cur_plugin_info_interface_version[MYSQL_MAX_PLUGIN_TYPE_NUM]=
 
 #include "sql_plugin_services.h"
 
+/*
+  A mutex LOCK_plugin_delete must be acquired before calling plugin_del
+  function. 
+*/
+mysql_mutex_t LOCK_plugin_delete;
+
 /*
   A mutex LOCK_plugin must be acquired before accessing the
   following variables/structures.
@@ -949,6 +956,7 @@ static void plugin_del(struct st_plugin_int *plugin)
 {
   DBUG_ENTER("plugin_del(plugin)");
   mysql_mutex_assert_owner(&LOCK_plugin);
+  mysql_mutex_assert_owner(&LOCK_plugin_delete);
   /* Free allocated strings before deleting the plugin. */
   mysql_rwlock_wrlock(&LOCK_system_variables_hash);
   mysql_del_sys_var_chain(plugin->system_vars);
@@ -996,11 +1004,14 @@ static void reap_plugins(void)
   while ((plugin= *(--list)))
     plugin_deinitialize(plugin, true);
 
+  mysql_mutex_lock(&LOCK_plugin_delete);
   mysql_mutex_lock(&LOCK_plugin);
 
   while ((plugin= *(--reap)))
     plugin_del(plugin);
 
+  mysql_mutex_unlock(&LOCK_plugin_delete);
+
   my_afree(reap);
 }
 
@@ -1205,10 +1216,12 @@ static inline void convert_underscore_to_dash(char *str, int len)
 
 #ifdef HAVE_PSI_INTERFACE
 static PSI_mutex_key key_LOCK_plugin;
+static PSI_mutex_key key_LOCK_plugin_delete;
 
 static PSI_mutex_info all_plugin_mutexes[]=
 {
-  { &key_LOCK_plugin, "LOCK_plugin", PSI_FLAG_GLOBAL}
+  { &key_LOCK_plugin, "LOCK_plugin", PSI_FLAG_GLOBAL},
+  { &key_LOCK_plugin_delete, "LOCK_plugin_delete", PSI_FLAG_GLOBAL}
 };
 
 static void init_plugin_psi_keys(void)
@@ -1259,6 +1272,7 @@ int plugin_init(int *argc, char **argv, int flags)
 
 
   mysql_mutex_init(key_LOCK_plugin, &LOCK_plugin, MY_MUTEX_INIT_FAST);
+  mysql_mutex_init(key_LOCK_plugin_delete, &LOCK_plugin_delete, MY_MUTEX_INIT_FAST);
 
   if (my_init_dynamic_array(&plugin_dl_array,
                             sizeof(struct st_plugin_dl *),16,16) ||
@@ -1401,8 +1415,10 @@ int plugin_init(int *argc, char **argv, int flags)
         plugin_ptr->load_option == PLUGIN_FORCE_PLUS_PERMANENT)
       reaped_mandatory_plugin= TRUE;
     plugin_deinitialize(plugin_ptr, true);
+    mysql_mutex_lock(&LOCK_plugin_delete);
     mysql_mutex_lock(&LOCK_plugin);
     plugin_del(plugin_ptr);
+    mysql_mutex_unlock(&LOCK_plugin_delete);
   }
 
   mysql_mutex_unlock(&LOCK_plugin);
@@ -1692,10 +1708,11 @@ void plugin_shutdown(void)
       }
 
     /*
-      It's perfectly safe not to lock LOCK_plugin, as there're no
-      concurrent threads anymore. But some functions called from here
-      use mysql_mutex_assert_owner(), so we lock the mutex to satisfy it
+      It's perfectly safe not to lock LOCK_plugin, LOCK_plugin_delete, as
+      there're no concurrent threads anymore. But some functions called from
+      here use mysql_mutex_assert_owner(), so we lock the mutex to satisfy it
     */
+    mysql_mutex_lock(&LOCK_plugin_delete);
     mysql_mutex_lock(&LOCK_plugin);
 
     /*
@@ -1718,9 +1735,11 @@ void plugin_shutdown(void)
     cleanup_variables(NULL, &global_system_variables);
     cleanup_variables(NULL, &max_system_variables);
     mysql_mutex_unlock(&LOCK_plugin);
+    mysql_mutex_unlock(&LOCK_plugin_delete);
 
     initialized= 0;
     mysql_mutex_destroy(&LOCK_plugin);
+    mysql_mutex_destroy(&LOCK_plugin_delete);
 
     my_afree(plugins);
   }
@@ -1795,6 +1814,7 @@ bool mysql_install_plugin(THD *thd, const LEX_STRING *name, const LEX_STRING *dl
   mysql_audit_acquire_plugins(thd, MYSQL_AUDIT_GENERAL_CLASS);
 
   mysql_mutex_lock(&LOCK_plugin);
+  DEBUG_SYNC(thd, "acquired_LOCK_plugin");
   mysql_rwlock_wrlock(&LOCK_system_variables_hash);
 
   if (my_load_defaults(MYSQL_CONFIG_NAME, load_default_groups, &argc, &argv, NULL))

sql/sql_plugin.h

@@ -40,6 +40,8 @@ extern const char *global_plugin_typelib_names[];
 
 #include <my_sys.h>
 
+extern mysql_mutex_t LOCK_plugin_delete;
+
 #ifdef DBUG_OFF
 #define plugin_ref_to_int(A) A
 #define plugin_int_to_ref(A) A

sql/sql_show.cc

@@ -6292,6 +6292,7 @@ int fill_open_tables(THD *thd, TABLE_LIST *tables, COND *cond)
 int fill_variables(THD *thd, TABLE_LIST *tables, COND *cond)
 {
   DBUG_ENTER("fill_variables");
+  SHOW_VAR *sys_var_array;
   int res= 0;
   LEX *lex= thd->lex;
   const char *wild= lex->wild ? lex->wild->ptr() : NullS;
@@ -6305,10 +6306,21 @@ int fill_variables(THD *thd, TABLE_LIST *tables, COND *cond)
       schema_table_idx == SCH_GLOBAL_VARIABLES)
     option_type= OPT_GLOBAL;
 
+  /*
+    Lock LOCK_plugin_delete to avoid deletion of any plugins while creating
+    SHOW_VAR array and hold it until all variables are stored in the table.
+  */
+  mysql_mutex_lock(&LOCK_plugin_delete);
+  // Lock LOCK_system_variables_hash to prepare SHOW_VARs array.
   mysql_rwlock_rdlock(&LOCK_system_variables_hash);
-  res= show_status_array(thd, wild, enumerate_sys_vars(thd, sorted_vars, option_type),
-                         option_type, NULL, "", tables->table, upper_case_names, cond);
+  DEBUG_SYNC(thd, "acquired_LOCK_system_variables_hash");
+  sys_var_array= enumerate_sys_vars(thd, sorted_vars, option_type);
   mysql_rwlock_unlock(&LOCK_system_variables_hash);
+
+  res= show_status_array(thd, wild, sys_var_array, option_type, NULL, "",
+                         tables->table, upper_case_names, cond);
+
+  mysql_mutex_unlock(&LOCK_plugin_delete);
   DBUG_RETURN(res);
 }