tracing: Add function probe to trigger stack traces

Add a function probe that will cause a stack trace to be traced in
the ring buffer when the given function(s) are called.

format is:

 <function>:stacktrace[:<count>]

 echo 'schedule:stacktrace' > /debug/tracing/set_ftrace_filter
 cat /debug/tracing/trace_pipe
     kworker/2:0-4329  [002] ...2  2933.558007: <stack trace>
 => kthread
 => ret_from_fork
          <idle>-0     [000] .N.2  2933.558019: <stack trace>
 => rest_init
 => start_kernel
 => x86_64_start_reservations
 => x86_64_start_kernel
     kworker/2:0-4329  [002] ...2  2933.558109: <stack trace>
 => kthread
 => ret_from_fork
[...]

This can be set to only trace a specific amount of times:

 echo 'schedule:stacktrace:3' > /debug/tracing/set_ftrace_filter
 cat /debug/tracing/trace_pipe
           <...>-58    [003] ...2   841.801694: <stack trace>
 => kthread
 => ret_from_fork
          <idle>-0     [001] .N.2   841.801697: <stack trace>
 => start_secondary
           <...>-2059  [001] ...2   841.801736: <stack trace>
 => wait_for_common
 => wait_for_completion
 => flush_work
 => tty_flush_to_ldisc
 => input_available_p
 => n_tty_poll
 => tty_poll
 => do_select
 => core_sys_select
 => sys_select
 => system_call_fastpath

To remove these:

 echo '!schedule:stacktrace' > /debug/tracing/set_ftrace_filter
 echo '!schedule:stacktrace:0' > /debug/tracing/set_ftrace_filter

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 115 insertions, 35 deletions

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 043b2425ae73..c4d6d7191988 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -265,56 +265,103 @@ ftrace_traceoff(unsigned long ip, unsigned long parent_ip, void **data)
         tracing_off();
 }
 
+/*
+ * Skip 4:
+ *   ftrace_stacktrace()
+ *   function_trace_probe_call()
+ *   ftrace_ops_list_func()
+ *   ftrace_call()
+ */
+#define STACK_SKIP 4
+
+static void
+ftrace_stacktrace(unsigned long ip, unsigned long parent_ip, void **data)
+{
+        trace_dump_stack(STACK_SKIP);
+}
+
+static void
+ftrace_stacktrace_count(unsigned long ip, unsigned long parent_ip, void **data)
+{
+        if (!tracing_is_on())
+                return;
+
+        if (update_count(data))
+                trace_dump_stack(STACK_SKIP);
+}
+
 static int
-ftrace_trace_onoff_print(struct seq_file *m, unsigned long ip,
-                         struct ftrace_probe_ops *ops, void *data);
+ftrace_probe_print(const char *name, struct seq_file *m,
+                   unsigned long ip, void *data)
+{
+        long count = (long)data;
+
+        seq_printf(m, "%ps:%s", (void *)ip, name);
+
+        if (count == -1)
+                seq_printf(m, ":unlimited\n");
+        else
+                seq_printf(m, ":count=%ld\n", count);
+
+        return 0;
+}
+
+static int
+ftrace_traceon_print(struct seq_file *m, unsigned long ip,
+                         struct ftrace_probe_ops *ops, void *data)
+{
+        return ftrace_probe_print("traceon", m, ip, data);
+}
+
+static int
+ftrace_traceoff_print(struct seq_file *m, unsigned long ip,
+                         struct ftrace_probe_ops *ops, void *data)
+{
+        return ftrace_probe_print("traceoff", m, ip, data);
+}
+
+static int
+ftrace_stacktrace_print(struct seq_file *m, unsigned long ip,
+                        struct ftrace_probe_ops *ops, void *data)
+{
+        return ftrace_probe_print("stacktrace", m, ip, data);
+}
 
 static struct ftrace_probe_ops traceon_count_probe_ops = {
         .func                   = ftrace_traceon_count,
-        .print                  = ftrace_trace_onoff_print,
+        .print                  = ftrace_traceon_print,
 };
 
 static struct ftrace_probe_ops traceoff_count_probe_ops = {
         .func                   = ftrace_traceoff_count,
-        .print                  = ftrace_trace_onoff_print,
+        .print                  = ftrace_traceoff_print,
+};
+
+static struct ftrace_probe_ops stacktrace_count_probe_ops = {
+        .func                   = ftrace_stacktrace_count,
+        .print                  = ftrace_stacktrace_print,
 };
 
 static struct ftrace_probe_ops traceon_probe_ops = {
         .func                   = ftrace_traceon,
-        .print                  = ftrace_trace_onoff_print,
+        .print                  = ftrace_traceon_print,
 };
 
 static struct ftrace_probe_ops traceoff_probe_ops = {
         .func                   = ftrace_traceoff,
-        .print                  = ftrace_trace_onoff_print,
+        .print                  = ftrace_traceoff_print,
 };
 
-static int
-ftrace_trace_onoff_print(struct seq_file *m, unsigned long ip,
-                         struct ftrace_probe_ops *ops, void *data)
-{
-        long count = (long)data;
-
-        seq_printf(m, "%ps:", (void *)ip);
-
-        if (ops == &traceon_probe_ops || ops == &traceon_count_probe_ops)
-                seq_printf(m, "traceon");
-        else
-                seq_printf(m, "traceoff");
-
-        if (count == -1)
-                seq_printf(m, ":unlimited\n");
-        else
-                seq_printf(m, ":count=%ld\n", count);
-
-        return 0;
-}
+static struct ftrace_probe_ops stacktrace_probe_ops = {
+        .func                   = ftrace_stacktrace,
+        .print                  = ftrace_stacktrace_print,
+};
 
 static int
-ftrace_trace_onoff_callback(struct ftrace_hash *hash,
-                            char *glob, char *cmd, char *param, int enable)
+ftrace_trace_probe_callback(struct ftrace_probe_ops *ops,
+                            struct ftrace_hash *hash, char *glob,
+                            char *cmd, char *param, int enable)
 {
-        struct ftrace_probe_ops *ops;
         void *count = (void *)-1;
         char *number;
         int ret;
@@ -323,12 +370,6 @@ ftrace_trace_onoff_callback(struct ftrace_hash *hash,
         if (!enable)
                 return -EINVAL;
 
-        /* we register both traceon and traceoff to this callback */
-        if (strcmp(cmd, "traceon") == 0)
-                ops = param ? &traceon_count_probe_ops : &traceon_probe_ops;
-        else
-                ops = param ? &traceoff_count_probe_ops : &traceoff_probe_ops;
-
         if (glob[0] == '!') {
                 unregister_ftrace_function_probe_func(glob+1, ops);
                 return 0;
@@ -356,6 +397,34 @@ ftrace_trace_onoff_callback(struct ftrace_hash *hash,
         return ret < 0 ? ret : 0;
 }
 
+static int
+ftrace_trace_onoff_callback(struct ftrace_hash *hash,
+                            char *glob, char *cmd, char *param, int enable)
+{
+        struct ftrace_probe_ops *ops;
+
+        /* we register both traceon and traceoff to this callback */
+        if (strcmp(cmd, "traceon") == 0)
+                ops = param ? &traceon_count_probe_ops : &traceon_probe_ops;
+        else
+                ops = param ? &traceoff_count_probe_ops : &traceoff_probe_ops;
+
+        return ftrace_trace_probe_callback(ops, hash, glob, cmd,
+                                           param, enable);
+}
+
+static int
+ftrace_stacktrace_callback(struct ftrace_hash *hash,
+                           char *glob, char *cmd, char *param, int enable)
+{
+        struct ftrace_probe_ops *ops;
+
+        ops = param ? &stacktrace_count_probe_ops : &stacktrace_probe_ops;
+
+        return ftrace_trace_probe_callback(ops, hash, glob, cmd,
+                                           param, enable);
+}
+
 static struct ftrace_func_command ftrace_traceon_cmd = {
         .name                   = "traceon",
         .func                   = ftrace_trace_onoff_callback,
@@ -366,6 +435,11 @@ static struct ftrace_func_command ftrace_traceoff_cmd = {
         .func                   = ftrace_trace_onoff_callback,
 };
 
+static struct ftrace_func_command ftrace_stacktrace_cmd = {
+        .name                   = "stacktrace",
+        .func                   = ftrace_stacktrace_callback,
+};
+
 static int __init init_func_cmd_traceon(void)
 {
         int ret;
@@ -377,6 +451,12 @@ static int __init init_func_cmd_traceon(void)
         ret = register_ftrace_command(&ftrace_traceon_cmd);
         if (ret)
                 unregister_ftrace_command(&ftrace_traceoff_cmd);
+
+        ret = register_ftrace_command(&ftrace_stacktrace_cmd);
+        if (ret) {
+                unregister_ftrace_command(&ftrace_traceoff_cmd);
+                unregister_ftrace_command(&ftrace_traceon_cmd);
+        }
         return ret;
 }
 #else