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MDEV-14485 Server hangs on startup in THD::init

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Solve 3 way deadlock between plugin_initialiaze(), THD::init() and
mysql_sys_var_char().

The deadlock exists because of the lock order inversion between
LOCK_global_system_variables mutex and LOCK_system_variables_hash
read-write lock-

In this case, it is enough to change LOCK_system_variables_hash to prefer
reads to fix the deadlock, i.e change it to mysql_prlock_t
This commit is contained in:
Vladislav Vaintroub
2018-01-27 17:46:31 +00:00
parent 1da063a45b
commit 7cdf759c86
6 changed files with 22 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
extra/mariabackup/xtrabackup.cc
View File

@ -5070,7 +5070,7 @@ handle_options(int argc, char **argv, char ***argv_client, char ***argv_server)
setup_error_messages();
sys_var_init();
plugin_mutex_init();
mysql_rwlock_init(key_rwlock_LOCK_system_variables_hash, &LOCK_system_variables_hash);
mysql_prlock_init(key_rwlock_LOCK_system_variables_hash, &LOCK_system_variables_hash);
opt_stack_trace = 1;
test_flags |= TEST_SIGINT;
init_signals();

6
sql/mysqld.cc
View File

@ -778,7 +778,7 @@ mysql_mutex_t LOCK_prepared_stmt_count;
mysql_mutex_t LOCK_des_key_file;
#endif
mysql_rwlock_t LOCK_grant, LOCK_sys_init_connect, LOCK_sys_init_slave;
mysql_rwlock_t LOCK_system_variables_hash;
mysql_prlock_t LOCK_system_variables_hash;
mysql_cond_t COND_thread_count, COND_start_thread;
pthread_t signal_thread;
pthread_attr_t connection_attrib;
@ -2354,7 +2354,7 @@ static void clean_up_mutexes()
mysql_rwlock_destroy(&LOCK_sys_init_connect);
mysql_rwlock_destroy(&LOCK_sys_init_slave);
mysql_mutex_destroy(&LOCK_global_system_variables);
mysql_rwlock_destroy(&LOCK_system_variables_hash);
mysql_prlock_destroy(&LOCK_system_variables_hash);
mysql_mutex_destroy(&LOCK_short_uuid_generator);
mysql_mutex_destroy(&LOCK_prepared_stmt_count);
mysql_mutex_destroy(&LOCK_error_messages);
@ -4680,7 +4680,7 @@ static int init_thread_environment()
&LOCK_global_system_variables, MY_MUTEX_INIT_FAST);
mysql_mutex_record_order(&LOCK_active_mi, &LOCK_global_system_variables);
mysql_mutex_record_order(&LOCK_status, &LOCK_thread_count);
mysql_rwlock_init(key_rwlock_LOCK_system_variables_hash,
mysql_prlock_init(key_rwlock_LOCK_system_variables_hash,
&LOCK_system_variables_hash);
mysql_mutex_init(key_LOCK_prepared_stmt_count,
&LOCK_prepared_stmt_count, MY_MUTEX_INIT_FAST);

2
sql/mysqld.h
View File

@ -577,7 +577,7 @@ extern mysql_mutex_t LOCK_des_key_file;
extern mysql_mutex_t LOCK_server_started;
extern mysql_cond_t COND_server_started;
extern mysql_rwlock_t LOCK_grant, LOCK_sys_init_connect, LOCK_sys_init_slave;
extern mysql_rwlock_t LOCK_system_variables_hash;
extern mysql_prlock_t LOCK_system_variables_hash;
extern mysql_cond_t COND_thread_count, COND_start_thread;
extern mysql_cond_t COND_manager;
extern mysql_cond_t COND_slave_background;

8
sql/set_var.cc
View File

@ -595,10 +595,10 @@ int mysql_del_sys_var_chain(sys_var *first)
{
int result= 0;
mysql_rwlock_wrlock(&LOCK_system_variables_hash);
mysql_prlock_wrlock(&LOCK_system_variables_hash);
for (sys_var *var= first; var; var= var->next)
result|= my_hash_delete(&system_variable_hash, (uchar*) var);
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
return result;
}
@ -1067,7 +1067,7 @@ int fill_sysvars(THD *thd, TABLE_LIST *tables, COND *cond)
cond= make_cond_for_info_schema(thd, cond, tables);
thd->count_cuted_fields= CHECK_FIELD_WARN;
mysql_rwlock_rdlock(&LOCK_system_variables_hash);
mysql_prlock_rdlock(&LOCK_system_variables_hash);
for (uint i= 0; i < system_variable_hash.records; i++)
{
@ -1229,7 +1229,7 @@ int fill_sysvars(THD *thd, TABLE_LIST *tables, COND *cond)
}
res= 0;
end:
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
thd->count_cuted_fields= save_count_cuted_fields;
return res;
}

22
sql/sql_plugin.cc
View File

@ -1394,10 +1394,10 @@ static int plugin_initialize(MEM_ROOT *tmp_root, struct st_plugin_int *plugin,
mysql_mutex_unlock(&LOCK_plugin);
mysql_rwlock_wrlock(&LOCK_system_variables_hash);
mysql_prlock_wrlock(&LOCK_system_variables_hash);
if (test_plugin_options(tmp_root, plugin, argc, argv))
state= PLUGIN_IS_DISABLED;
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
if (options_only || state == PLUGIN_IS_DISABLED)
{
@ -2797,11 +2797,11 @@ sys_var *find_sys_var_ex(THD *thd, const char *str, size_t length,
if (!locked)
mysql_mutex_lock(&LOCK_plugin);
mysql_rwlock_rdlock(&LOCK_system_variables_hash);
mysql_prlock_rdlock(&LOCK_system_variables_hash);
if ((var= intern_find_sys_var(str, length)) &&
(pi= var->cast_pluginvar()))
{
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
LEX *lex= thd ? thd->lex : 0;
if (!(plugin= intern_plugin_lock(lex, plugin_int_to_ref(pi->plugin))))
var= NULL; /* failed to lock it, it must be uninstalling */
@ -2814,7 +2814,7 @@ sys_var *find_sys_var_ex(THD *thd, const char *str, size_t length,
}
}
else
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
if (!locked)
mysql_mutex_unlock(&LOCK_plugin);
@ -3043,9 +3043,9 @@ static uchar *intern_sys_var_ptr(THD* thd, int offset, bool global_lock)
if (!thd->variables.dynamic_variables_ptr ||
(uint)offset > thd->variables.dynamic_variables_head)
{
mysql_rwlock_rdlock(&LOCK_system_variables_hash);
mysql_prlock_rdlock(&LOCK_system_variables_hash);
sync_dynamic_session_variables(thd, global_lock);
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
}
DBUG_RETURN((uchar*)thd->variables.dynamic_variables_ptr + offset);
}
@ -3160,7 +3160,7 @@ static void cleanup_variables(struct system_variables *vars)
st_bookmark *v;
uint idx;
mysql_rwlock_rdlock(&LOCK_system_variables_hash);
mysql_prlock_rdlock(&LOCK_system_variables_hash);
for (idx= 0; idx < bookmark_hash.records; idx++)
{
v= (st_bookmark*) my_hash_element(&bookmark_hash, idx);
@ -3179,7 +3179,7 @@ static void cleanup_variables(struct system_variables *vars)
*ptr= NULL;
}
}
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
DBUG_ASSERT(vars->table_plugin == NULL);
DBUG_ASSERT(vars->tmp_table_plugin == NULL);
@ -4234,10 +4234,10 @@ int thd_key_create(MYSQL_THD_KEY_T *key)
PLUGIN_VAR_NOSYSVAR | PLUGIN_VAR_NOCMDOPT;
char namebuf[256];
snprintf(namebuf, sizeof(namebuf), "%u", thd_key_no++);
mysql_rwlock_wrlock(&LOCK_system_variables_hash);
mysql_prlock_wrlock(&LOCK_system_variables_hash);
// non-letters in the name as an extra safety
st_bookmark *bookmark= register_var("\a\v\a\t\a\r", namebuf, flags);
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
if (bookmark)
{
*key= bookmark->offset;

4
sql/sql_show.cc
View File

@ -7399,7 +7399,7 @@ int fill_variables(THD *thd, TABLE_LIST *tables, COND *cond)
COND *partial_cond= make_cond_for_info_schema(thd, cond, tables);
mysql_rwlock_rdlock(&LOCK_system_variables_hash);
mysql_prlock_rdlock(&LOCK_system_variables_hash);
/*
Avoid recursive LOCK_system_variables_hash acquisition in
@ -7414,7 +7414,7 @@ int fill_variables(THD *thd, TABLE_LIST *tables, COND *cond)
res= show_status_array(thd, wild, enumerate_sys_vars(thd, sorted_vars, scope),
scope, NULL, "", tables->table,
upper_case_names, partial_cond);
mysql_rwlock_unlock(&LOCK_system_variables_hash);
mysql_prlock_unlock(&LOCK_system_variables_hash);
DBUG_RETURN(res);
}