Fix for:

Bug #4810 "deadlock with KILL when the victim was in a wait state"
(I included mutex unlock into exit_cond() for future safety)
and BUG#4827 "KILL while START SLAVE may lead to replication slave crash"


sql/lock.cc:
  we did exit_cond() before unlock(LOCK_open), which led to deadlocks with THD::awake(). Fixing this.
sql/log.cc:
  mutex unlock is now included in exit_cond()
sql/repl_failsafe.cc:
  we did exit_cond() before unlock(LOCK_rpl_status), which led to deadlocks with THD::awake(). Fixing this.
sql/slave.cc:
  we did exit_cond() before unlock(cond_lock), which led to deadlocks with THD::awake(). Fixing this.
  Fixing also that if killed while waiting for slave thread to start, we don't release the mutex
  (that caused a double release of the mutex => crash).
sql/sql_class.h:
  comments about exit_cond()/enter_cond().
  Mutex unlock is now included in exit_cond() so that it's always done in the good order.
sql/sql_table.cc:
  unlock is now included in exit_cond().

1 files changed, 5 insertions, 4 deletions

diff --git a/sql/repl_failsafe.cc b/sql/repl_failsafe.cc
index 1edf452d5f6..604938a8ed0 100644
--- a/sql/repl_failsafe.cc
+++ b/sql/repl_failsafe.cc
@@ -584,6 +584,8 @@ pthread_handler_decl(handle_failsafe_rpl,arg)
   THD *thd = new THD;
   thd->thread_stack = (char*)&thd;
   MYSQL* recovery_captain = 0;
+  const char* msg;
+
   pthread_detach_this_thread();
   if (init_failsafe_rpl_thread(thd) || !(recovery_captain=mc_mysql_init(0)))
   {
@@ -591,11 +593,11 @@ pthread_handler_decl(handle_failsafe_rpl,arg)
     goto err;
   }
   pthread_mutex_lock(&LOCK_rpl_status);
+  msg= thd->enter_cond(&COND_rpl_status,
+                       &LOCK_rpl_status, "Waiting for request");
   while (!thd->killed && !abort_loop)
   {
     bool break_req_chain = 0;
-    const char* msg = thd->enter_cond(&COND_rpl_status,
-				      &LOCK_rpl_status, "Waiting for request");
     pthread_cond_wait(&COND_rpl_status, &LOCK_rpl_status);
     thd->proc_info="Processing request";
     while (!break_req_chain)
@@ -613,9 +615,8 @@ pthread_handler_decl(handle_failsafe_rpl,arg)
 	break;
       }
     }
-    thd->exit_cond(msg);
   }
-  pthread_mutex_unlock(&LOCK_rpl_status);
+  thd->exit_cond(msg);
 err:
   if (recovery_captain)
     mc_mysql_close(recovery_captain);