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Move all kill mutex protection to LOCK_thd_kill

Browse Source 
LOCK_thd_data was used to protect both THD data and
ensure that the THD is not deleted while it was in use

This patch moves the THD delete protection to LOCK_thd_kill,
which already protects the THD for kill.

The benefits are:
- More well defined what LOCK_thd_data protects
- LOCK_thd_data usage is now much simpler and easier to verify
- Less chance of deadlocks in SHOW PROCESS LIST as there is less
  chance of interactions between mutexes
- Remove not needed LOCK_thread_count from
  thd_get_error_context_description()
- Fewer mutex taken for thd->awake()

Other things:
- Don't take mysys->var mutex in show processlist to check if thread
  is kill marked
- thd->awake() now automatically takes the LOCK_thd_kill mutex
  (Simplifies code)
- Apc uses LOCK_thd_kill instead of LOCK_thd_data
This commit is contained in:
Monty
2017-12-07 21:28:00 +02:00
parent 3574f9c7bc
commit c2118a08b1
15 changed files with 109 additions and 120 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
sql/sql_parse.cc
View File

@ -8758,13 +8758,13 @@ void add_join_natural(TABLE_LIST *a, TABLE_LIST *b, List<String> *using_fields,
/**
Find a thread by id and return it, locking it LOCK_thd_data
Find a thread by id and return it, locking it LOCK_thd_kill
@param id Identifier of the thread we're looking for
@param query_id If true, search by query_id instead of thread_id
@return NULL - not found
pointer - thread found, and its LOCK_thd_data is locked.
pointer - thread found, and its LOCK_thd_kill is locked.
*/
THD *find_thread_by_id(longlong id, bool query_id)
@ -8778,7 +8778,7 @@ THD *find_thread_by_id(longlong id, bool query_id)
continue;
if (id == (query_id ? tmp->query_id : (longlong) tmp->thread_id))
{
mysql_mutex_lock(&tmp->LOCK_thd_data); // Lock from delete
mysql_mutex_lock(&tmp->LOCK_thd_kill); // Lock from delete
break;
}
}
@ -8834,13 +8834,13 @@ kill_one_thread(THD *thd, longlong id, killed_state kill_signal, killed_type typ
thd->security_ctx->user_matches(tmp->security_ctx)) &&
!wsrep_thd_is_BF(tmp, true))
{
tmp->awake(kill_signal);
tmp->awake_no_mutex(kill_signal);
error=0;
}
else
error= (type == KILL_TYPE_QUERY ? ER_KILL_QUERY_DENIED_ERROR :
ER_KILL_DENIED_ERROR);
mysql_mutex_unlock(&tmp->LOCK_thd_data);
mysql_mutex_unlock(&tmp->LOCK_thd_kill);
}
DBUG_PRINT("exit", ("%d", error));
DBUG_RETURN(error);
@ -8898,7 +8898,7 @@ static uint kill_threads_for_user(THD *thd, LEX_USER *user,
DBUG_RETURN(ER_KILL_DENIED_ERROR);
}
if (!threads_to_kill.push_back(tmp, thd->mem_root))
mysql_mutex_lock(&tmp->LOCK_thd_data); // Lock from delete
mysql_mutex_lock(&tmp->LOCK_thd_kill); // Lock from delete
}
}
mysql_mutex_unlock(&LOCK_thread_count);
@ -8909,17 +8909,17 @@ static uint kill_threads_for_user(THD *thd, LEX_USER *user,
THD *ptr= it2++;
do
{
ptr->awake(kill_signal);
ptr->awake_no_mutex(kill_signal);
/*
Careful here: The list nodes are allocated on the memroots of the
THDs to be awakened.
But those THDs may be terminated and deleted as soon as we release
LOCK_thd_data, which will make the list nodes invalid.
LOCK_thd_kill, which will make the list nodes invalid.
Since the operation "it++" dereferences the "next" pointer of the
previous list node, we need to do this while holding LOCK_thd_data.
previous list node, we need to do this while holding LOCK_thd_kill.
*/
next_ptr= it2++;
mysql_mutex_unlock(&ptr->LOCK_thd_data);
mysql_mutex_unlock(&ptr->LOCK_thd_kill);
(*rows)++;
} while ((ptr= next_ptr));
}