powerpc/ftrace: Fix the comments for ftrace_modify_code

There is no need to worry about module and __init text disappearing
case, because that ftrace has a module notifier that is called when a
module is being unloaded and before the text goes away and this code
grabs the ftrace_lock mutex and removes the module functions from the
ftrace list, such that it will no longer do any modifications to that
module's text, the update to make functions be traced or not is done
under the ftrace_lock mutex as well. And by now, __init section codes
should not been modified by ftrace, because it is black listed in
recordmcount.c and ignored by ftrace.
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Li Bin <huawei.libin@huawei.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/ftrace.c

@@ -47,13 +47,11 @@ ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new)
 	unsigned int replaced;
 
 	/*
-	 * Note: Due to modules and __init, code can
-	 *  disappear and change, we need to protect against faulting
-	 *  as well as code changing. We do this by using the
-	 *  probe_kernel_* functions.
-	 *
-	 * No real locking needed, this code is run through
-	 * kstop_machine, or before SMP starts.
+	 * Note:
+	 * We are paranoid about modifying text, as if a bug was to happen, it
+	 * could cause us to read or write to someplace that could cause harm.
+	 * Carefully read and modify the code with probe_kernel_*(), and make
+	 * sure what we read is what we expected it to be before modifying it.
 	 */
 
 	/* read the text we want to modify */