bzr commit into mysql-5.1 branch (sven.sandberg:3625) Bug#12574820

[Sven Sandberg]

#At file:///home/sven/bzr/b12574820-reset_logs_lock_order/5.1/ based on revid:vasil.dimov@stripped

 3625 Sven Sandberg	2011-05-23
      BUG#12574820: binlog.binlog_tmp_table timing out in daily and weekly trunk run
      Problem: MYSQL_BIN_LOG::reset_logs acquires mutexes in wrong order.
      The correct order is first LOCK_thread_count and then LOCK_log. This function
      does it the other way around. This leads to deadlock when run in parallel
      with a thread that takes the two locks in correct order. For example, a thread
      that disconnects will take the locks in the correct order.
      Fix: change order of the locks in MYSQL_BIN_LOG::reset_logs:
      first LOCK_thread_count and then LOCK_log.
      It is not possible to create a deterministic test case where RESET MASTER
      deadlocks with a thread that is disconnecting: that would require a debug_sync
      point, but the debug_sync feature shuts down for the disconnecting thread
      before it acquires LOCK_thread_count.
     @ sql/log.cc
        Change mutex acquisition to the correct order:
        first LOCK_thread_count, then LOCK_log.

    modified:
      sql/log.cc
=== modified file 'sql/log.cc'
--- a/sql/log.cc	2011-02-22 21:03:32 +0000
+++ b/sql/log.cc	2011-05-23 15:28:50 +0000
@@ -2989,12 +2989,6 @@ bool MYSQL_BIN_LOG::reset_logs(THD* thd)
   DBUG_ENTER("reset_logs");
 
   ha_reset_logs(thd);
-  /*
-    We need to get both locks to be sure that no one is trying to
-    write to the index log file.
-  */
-  pthread_mutex_lock(&LOCK_log);
-  pthread_mutex_lock(&LOCK_index);
 
   /*
     The following mutex is needed to ensure that no threads call
@@ -3002,7 +2996,14 @@ bool MYSQL_BIN_LOG::reset_logs(THD* thd)
     thread. If the transaction involved MyISAM tables, it should go
     into binlog even on rollback.
   */
-  VOID(pthread_mutex_lock(&LOCK_thread_count));
+  pthread_mutex_lock(&LOCK_thread_count);
+
+  /*
+    We need to get both locks to be sure that no one is trying to
+    write to the index log file.
+  */
+  pthread_mutex_lock(&LOCK_log);
+  pthread_mutex_lock(&LOCK_index);
 
   /* Save variables so that we can reopen the log */
   save_name=name;


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