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>

2 files changed, 19 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fd5c913c33c1..fde2ae06539a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2435,6 +2435,14 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
         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
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 0398b7c7afd6..d4545f49242e 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -13,6 +13,9 @@
 #include <linux/sysctl.h>
 #include <linux/init.h>
 #include <linux/fs.h>
+
+#include <asm/setup.h>
+
 #include "trace.h"
 
 #define STACK_TRACE_ENTRIES 500
@@ -352,8 +355,13 @@ stack_trace_sysctl(struct ctl_table *table, int write,
         return ret;
 }
 
+static char stack_trace_filter_buf[COMMAND_LINE_SIZE+1] __initdata;
+
 static __init int enable_stacktrace(char *str)
 {
+        if (strncmp(str, "_filter=", 8) == 0)
+                strncpy(stack_trace_filter_buf, str+8, COMMAND_LINE_SIZE);
+
         stack_tracer_enabled = 1;
         last_stack_tracer_enabled = 1;
         return 1;
@@ -375,6 +383,9 @@ static __init int stack_trace_init(void)
         trace_create_file("stack_trace_filter", 0444, d_tracer,
                         NULL, &stack_trace_filter_fops);
 
+        if (stack_trace_filter_buf[0])
+                ftrace_set_early_filter(&trace_ops, stack_trace_filter_buf, 1);
+
         if (stack_tracer_enabled)
                 register_ftrace_function(&trace_ops);