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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
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4
sql/sql_show.cc
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@ -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);
}