From fea1524dbfb413820ba3594064da658c22417671 Mon Sep 17 00:00:00 2001
From: unknown <thek@adventure.(none)>
Date: Mon, 26 Nov 2007 15:44:05 +0100
Subject: [PATCH] Bug #32436 KILL QUERY completely deadlocks mysqld

Sending several "KILL QUERY" statements to target a connection running
"SELECT SLEEP" could freeze the server.

The locking order in Item_func_sleep was wrong and this could lead to a
dead lock.

This patch solves the issue by resolving the locking order properly.


sql/item_func.cc:
  - Moved LOCK_user_locks critical region so that it doesn't share space with
    mysys_var->mutex region; this can lead to deadlock.
---
 sql/item_func.cc | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/sql/item_func.cc b/sql/item_func.cc
index d03d497dfd0..a0824f2a146 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -3732,13 +3732,12 @@ longlong Item_func_sleep::val_int()
       break;
     error= 0;
   }
-
+  pthread_mutex_unlock(&LOCK_user_locks);
   pthread_mutex_lock(&thd->mysys_var->mutex);
   thd->mysys_var->current_mutex= 0;
   thd->mysys_var->current_cond=  0;
   pthread_mutex_unlock(&thd->mysys_var->mutex);
 
-  pthread_mutex_unlock(&LOCK_user_locks);
   pthread_cond_destroy(&cond);
 
   return test(!error); 		// Return 1 killed