CRED: Rename cred_exec_mutex to reflect that it's a guard against ptrace

Rename cred_exec_mutex to reflect that it's a guard against foreign
intervention on a process's credential state, such as is made by ptrace().  The
attachment of a debugger to a process affects execve()'s calculation of the new
credential state - _and_ also setprocattr()'s calculation of that state.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index d87247d..7f54ba9 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -145,8 +145,8 @@
 	.group_leader	= &tsk,						\
 	.real_cred	= &init_cred,					\
 	.cred		= &init_cred,					\
-	.cred_exec_mutex =						\
-		 __MUTEX_INITIALIZER(tsk.cred_exec_mutex),		\
+	.cred_guard_mutex =						\
+		 __MUTEX_INITIALIZER(tsk.cred_guard_mutex),		\
 	.comm		= "swapper",					\
 	.thread		= INIT_THREAD,					\
 	.fs		= &init_fs,					\