Hi, Nikita! Looks good so far but I noticed too late that it's just one patch on top of others, not a complete thing. See few comments below. Shall I review everything? Is it feature complete except that it skips inactive threads? On Sep 07, Nikita Malyavin wrote:
revision-id: 9e1c15355a9 (mariadb-10.6.3-44-g9e1c15355a9) parent(s): d7c36600144 author: Nikita Malyavin committer: Nikita Malyavin timestamp: 2021-09-07 18:37:51 +0300 message:
resolve the possible deadlock issue through intern_plugin_lock
diff --git a/sql/sql_plugin.cc b/sql/sql_plugin.cc index be043bf229a..ecd885ed296 100644 --- a/sql/sql_plugin.cc +++ b/sql/sql_plugin.cc @@ -1053,6 +1053,15 @@ plugin_ref plugin_lock(THD *thd, plugin_ref ptr) }
this needs a function comment. the function is quite specialized and very different from normal plugin lock functions. it requires a THD (normally it's optional), it does not return a locked plugin like the others (because, exactly, it's stored in the THD). because it's not what people usually expect from a plugin_lock* function, the comment should describe all these differences.
+void plugin_lock_by_var_if_different(THD *thd, sys_var *var, sys_var *var_prev) +{ + sys_var_pluginvar *pv= var->cast_pluginvar(); + sys_var_pluginvar *pv_prev= var_prev ? var_prev->cast_pluginvar() : NULL; + if (pv && (!pv_prev || pv->plugin != pv_prev->plugin)) + intern_plugin_lock(thd->lex, plugin_int_to_ref(pv->plugin)); +} + + /* Notes on lifetime:
diff --git a/storage/perfschema/pfs_variable.cc b/storage/perfschema/pfs_variable.cc index 984b68e699b..85656532c72 100644 --- a/storage/perfschema/pfs_variable.cc +++ b/storage/perfschema/pfs_variable.cc @@ -100,6 +102,15 @@ bool PFS_system_variable_cache::init_show_var_array(enum_var_type scope, bool st
mysql_prlock_unlock(&LOCK_system_variables_hash);
+ for (uint i= 0; i < m_show_var_array.elements(); i++)
why separately, not in the loop above?
+ { + sys_var *var= (sys_var *)m_show_var_array.at(i).value; + if (!var) continue;
can var be NULL?
+ sys_var *prev= i == 0 ? NULL : (sys_var *)m_show_var_array.at(i-1).value;
hmm, normally this is done with sys_var *prev= NULL; before the loop and prev= var; in the loop, after plugin_lock_by_var_if_different().
+ + plugin_lock_by_var_if_different(m_current_thd, var, prev); + } + /* Increase cache size if necessary. */ m_cache.reserve(m_show_var_array.elements());
@@ -316,7 +327,27 @@ class PFS_system_variable_cache_apc: public Apc_target::Apc_call
void call_in_target_thread() override { - (m_pfs->*m_func)(m_param); + call(m_pfs, m_func, m_param); + } +public: + static void call(PFS_system_variable_cache *pfs, Request func, uint param) + { + THD *safe_thd= pfs->safe_thd(); + + if (pfs->query_scope() == OPT_SESSION)
what's the point doing apc call if the query_scope() is not OPT_SESSION? It seems like here you need a DBUG_ASSERT, and the if() should be much earlier up the stack.
+ { + mysql_mutex_lock(&LOCK_global_system_variables); + if (!safe_thd->variables.dynamic_variables_ptr || + global_system_variables.dynamic_variables_head > + safe_thd->variables.dynamic_variables_head) + { + mysql_prlock_rdlock(&LOCK_system_variables_hash); + sync_dynamic_session_variables(safe_thd, false); + mysql_prlock_unlock(&LOCK_system_variables_hash); + } + mysql_mutex_unlock(&LOCK_global_system_variables); + } + (pfs->*func)(param); } };
Regards, Sergei VP of MariaDB Server Engineering and security@mariadb.org