tracing: Have stack tracing set filtered functions at boot

Add stacktrace_filter= to the kernel command line that lets
the user pick specific functions to check the stack on.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fd5c913..fde2ae0 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2435,6 +2435,14 @@
 	stacktrace	[FTRACE]
 			Enabled the stack tracer on boot up.
 
+	stacktrace_filter=[function-list]
+			[FTRACE] Limit the functions that the stack tracer
+			will trace at boot up. function-list is a comma separated
+			list of functions. This list can be changed at run
+			time by the stack_trace_filter file in the debugfs
+			tracing directory. Note, this enables stack tracing
+			and the stacktrace above is not needed.
+
 	sti=		[PARISC,HW]
 			Format: <num>
 			Set the STI (builtin display/keyboard on the HP-PARISC