Bug#46013: rpl_extraColmaster_myisam fails on pb2

Davi Arnaut · Davi Arnaut · commit 97dbd987f0f7 · 2009-08-13T17:07:20.000-03:00
Bug#45243: crash on win in sql thread clear_tables_to_lock() -&gt; free()
Bug#45242: crash on win in mysql_close() -&gt; free()
Bug#45238: rpl_slave_skip, rpl_change_master failed (lost connection) for STOP SLAVE
Bug#46030: rpl_truncate_3innodb causes server crash on windows
Bug#46014: rpl_stm_reset_slave crashes the server sporadically in pb2

When killing a user session on the server, it's necessary to
interrupt (notify) the thread associated with the session that
the connection is being killed so that the thread is woken up
if waiting for I/O. On a few platforms (Mac, Windows and HP-UX)
where the SIGNAL_WITH_VIO_CLOSE flag is defined, this interruption
procedure is to asynchronously close the underlying socket of
the connection.

In order to enable this schema, each connection serving thread
registers its VIO (I/O interface) so that other threads can
access it and close the connection. But only the owner thread of
the VIO might delete it as to guarantee that other threads won't
see freed memory (the thread unregisters the VIO before deleting
it). A side note: closing the socket introduces a harmless race
that might cause a thread attempt to read from a closed socket,
but this is deemed acceptable.

The problem is that this infrastructure was meant to only be used
by server threads, but the slave I/O thread was registering the
VIO of a mysql handle (a client API structure that represents a
connection to another server instance) as a active connection of
the thread. But under some circumstances such as network failures,
the client API might destroy the VIO associated with a handle at
will, yet the VIO wouldn't be properly unregistered. This could
lead to accesses to freed data if a thread attempted to kill a
slave I/O thread whose connection was already broken.

There was a attempt to work around this by checking whether
the socket was being interrupted, but this hack didn't work as
intended due to the aforementioned race -- attempting to read
from the socket would yield a "bad file descriptor" error.

The solution is to add a hook to the client API that is called
from the client code before the VIO of a handle is deleted.
This hook allows the slave I/O thread to detach the active vio
so it does not point to freed memory.
diff --git a/server-tools/instance-manager/mysql_connection.cc b/server-tools/instance-manager/mysql_connection.cc
@@ -120,6 +120,18 @@ void my_net_local_init(NET *net)
 
 C_MODE_END
 
+/*
+  Unused stub hook required for linking the client API.
+*/
+
+C_MODE_START
+
+void slave_io_thread_detach_vio()
+{
+}
+
+C_MODE_END
+
 
 /*
   Every resource, which we can fail to acquire, is allocated in init().
diff --git a/sql-common/client.c b/sql-common/client.c
@@ -911,6 +911,9 @@ void end_server(MYSQL *mysql)
   {
     init_sigpipe_variables
     DBUG_PRINT("info",("Net: %s", vio_description(mysql->net.vio)));
+#ifdef MYSQL_SERVER
+    slave_io_thread_detach_vio();
+#endif
     set_sigpipe(mysql);
     vio_delete(mysql->net.vio);
     reset_sigpipe(mysql);
diff --git a/sql/client_settings.h b/sql/client_settings.h
@@ -33,3 +33,11 @@
 
 #define mysql_server_init(a,b,c) 0
 
+#ifdef HAVE_REPLICATION
+C_MODE_START
+void slave_io_thread_detach_vio();
+C_MODE_END
+#else
+#define slave_io_thread_detach_vio()
+#endif
+
diff --git a/sql/slave.cc b/sql/slave.cc
@@ -4737,6 +4737,31 @@ void end_relay_log_info(RELAY_LOG_INFO* rli)
   DBUG_VOID_RETURN;
 }
 
+
+/**
+  Hook to detach the active VIO before closing a connection handle.
+
+  The client API might close the connection (and associated data)
+  in case it encounters a unrecoverable (network) error. This hook
+  is called from the client code before the VIO handle is deleted
+  allows the thread to detach the active vio so it does not point
+  to freed memory.
+
+  Other calls to THD::clear_active_vio throughout this module are
+  redundant due to the hook but are left in place for illustrative
+  purposes.
+*/
+
+extern "C" void slave_io_thread_detach_vio()
+{
+#ifdef SIGNAL_WITH_VIO_CLOSE
+  THD *thd= current_thd;
+  if (thd->slave_thread)
+    thd->clear_active_vio();
+#endif
+}
+
+
 /*
   Try to connect until successful or slave killed
 
