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MDEV-10010 - Recursive call to mysql_rwlock_rdlock for LOCK_system_variables_hash

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Avoid recursive LOCK_system_variables_hash acquisition in
intern_sys_var_ptr() by pre-syncing dynamic session variables.
This commit is contained in:
Sergey Vojtovich
2016-06-27 15:01:22 +04:00
parent 95c286cedf
commit ecb27d2650
3 changed files with 77 additions and 60 deletions
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47
sql/sql_plugin.cc
View File

@@ -2955,31 +2955,11 @@ static st_bookmark *register_var(const char *plugin, const char *name,
return result;
}
/*
returns a pointer to the memory which holds the thd-local variable or
a pointer to the global variable if thd==null.
If required, will sync with global variables if the requested variable
has not yet been allocated in the current thread.
*/
static uchar *intern_sys_var_ptr(THD* thd, int offset, bool global_lock)
{
DBUG_ENTER("intern_sys_var_ptr");
DBUG_ASSERT(offset >= 0);
DBUG_ASSERT((uint)offset <= global_system_variables.dynamic_variables_head);
if (!thd)
DBUG_RETURN((uchar*) global_system_variables.dynamic_variables_ptr + offset);
/*
dynamic_variables_head points to the largest valid offset
*/
if (!thd->variables.dynamic_variables_ptr ||
(uint)offset > thd->variables.dynamic_variables_head)
void sync_dynamic_session_variables(THD* thd, bool global_lock)
{
uint idx;
mysql_rwlock_rdlock(&LOCK_system_variables_hash);
thd->variables.dynamic_variables_ptr= (char*)
my_realloc(thd->variables.dynamic_variables_ptr,
global_variables_dynamic_size,
@@ -3036,7 +3016,32 @@ static uchar *intern_sys_var_ptr(THD* thd, int offset, bool global_lock)
global_system_variables.dynamic_variables_head;
thd->variables.dynamic_variables_size=
global_system_variables.dynamic_variables_size;
}
/*
returns a pointer to the memory which holds the thd-local variable or
a pointer to the global variable if thd==null.
If required, will sync with global variables if the requested variable
has not yet been allocated in the current thread.
*/
static uchar *intern_sys_var_ptr(THD* thd, int offset, bool global_lock)
{
DBUG_ENTER("intern_sys_var_ptr");
DBUG_ASSERT(offset >= 0);
DBUG_ASSERT((uint)offset <= global_system_variables.dynamic_variables_head);
if (!thd)
DBUG_RETURN((uchar*) global_system_variables.dynamic_variables_ptr + offset);
/*
dynamic_variables_head points to the largest valid offset
*/
if (!thd->variables.dynamic_variables_ptr ||
(uint)offset > thd->variables.dynamic_variables_head)
{
mysql_rwlock_rdlock(&LOCK_system_variables_hash);
sync_dynamic_session_variables(thd, global_lock);
mysql_rwlock_unlock(&LOCK_system_variables_hash);
}
DBUG_RETURN((uchar*)thd->variables.dynamic_variables_ptr + offset);

1
sql/sql_plugin.h
View File

@@ -190,4 +190,5 @@ extern bool plugin_foreach_with_mask(THD *thd, plugin_foreach_func *func,
extern bool plugin_dl_foreach(THD *thd, const LEX_STRING *dl,
plugin_foreach_func *func, void *arg);
extern void sync_dynamic_session_variables(THD* thd, bool global_lock);
#endif

11
sql/sql_show.cc
View File

@@ -7209,6 +7209,17 @@ 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);
/*
Avoid recursive LOCK_system_variables_hash acquisition in
intern_sys_var_ptr() by pre-syncing dynamic session variables.
*/
if (scope == OPT_SESSION &&
(!thd->variables.dynamic_variables_ptr ||
global_system_variables.dynamic_variables_head >
thd->variables.dynamic_variables_head))
sync_dynamic_session_variables(thd, true);
res= show_status_array(thd, wild, enumerate_sys_vars(thd, sorted_vars, scope),
scope, NULL, "", tables->table,
upper_case_names, partial_cond);