Merge tag 'trace-v6.14-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing fixes from Steven Rostedt:

 - Fix crash from bad histogram entry

   An error path in the histogram creation could leave an entry in a
   link list that gets freed. Then when a new entry is added it can
   cause a u-a-f bug. This is fixed by restructuring the code so that
   the histogram is consistent on failure and everything is cleaned up
   appropriately.

 - Fix fprobe self test

   The fprobe self test relies on no function being attached by ftrace.
   BPF programs can attach to functions via ftrace and systemd now does
   so. This causes those functions to appear in the enabled_functions
   list which holds all functions attached by ftrace. The selftest also
   uses that file to see if functions are being connected correctly. It
   counts the functions in the file, but if there's already functions in
   the file, it fails. Instead, add the number of functions in the file
   at the start of the test to all the calculations during the test.

 - Fix potential division by zero of the function profiler stddev

   The calculated divisor that calculates the standard deviation of the
   function times can overflow. If the overflow happens to land on zero,
   that can cause a division by zero. Check for zero from the
   calculation before doing the division.

   TODO: Catch when it ever overflows and report it accordingly. For
   now, just prevent the system from crashing.

* tag 'trace-v6.14-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ftrace: Avoid potential division by zero in function_stat_show()
  selftests/ftrace: Let fprobe test consider already enabled functions
  tracing: Fix bad hist from corrupting named_triggers list

2 files changed, 27 insertions, 30 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 6b0c25761ccb..fc88e0688daf 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -540,6 +540,7 @@ static int function_stat_show(struct seq_file *m, void *v)
 	static struct trace_seq s;
 	unsigned long long avg;
 	unsigned long long stddev;
+	unsigned long long stddev_denom;
 #endif
 	guard(mutex)(&ftrace_profile_lock);
 
@@ -559,23 +560,19 @@ static int function_stat_show(struct seq_file *m, void *v)
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	seq_puts(m, "    ");
 
-	/* Sample standard deviation (s^2) */
-	if (rec->counter <= 1)
-		stddev = 0;
-	else {
-		/*
-		 * Apply Welford's method:
-		 * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
-		 */
+	/*
+	 * Variance formula:
+	 * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
+	 * Maybe Welford's method is better here?
+	 * Divide only by 1000 for ns^2 -> us^2 conversion.
+	 * trace_print_graph_duration will divide by 1000 again.
+	 */
+	stddev = 0;
+	stddev_denom = rec->counter * (rec->counter - 1) * 1000;
+	if (stddev_denom) {
 		stddev = rec->counter * rec->time_squared -
 			 rec->time * rec->time;
-
-		/*
-		 * Divide only 1000 for ns^2 -> us^2 conversion.
-		 * trace_print_graph_duration will divide 1000 again.
-		 */
-		stddev = div64_ul(stddev,
-				  rec->counter * (rec->counter - 1) * 1000);
+		stddev = div64_ul(stddev, stddev_denom);
 	}
 
 	trace_seq_init(&s);
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 261163b00137..ad7419e24055 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -6724,27 +6724,27 @@ static int event_hist_trigger_parse(struct event_command *cmd_ops,
 	if (existing_hist_update_only(glob, trigger_data, file))
 		goto out_free;
 
-	ret = event_trigger_register(cmd_ops, file, glob, trigger_data);
-	if (ret < 0)
-		goto out_free;
+	if (!get_named_trigger_data(trigger_data)) {
 
-	if (get_named_trigger_data(trigger_data))
-		goto enable;
+		ret = create_actions(hist_data);
+		if (ret)
+			goto out_free;
 
-	ret = create_actions(hist_data);
-	if (ret)
-		goto out_unreg;
+		if (has_hist_vars(hist_data) || hist_data->n_var_refs) {
+			ret = save_hist_vars(hist_data);
+			if (ret)
+				goto out_free;
+		}
 
-	if (has_hist_vars(hist_data) || hist_data->n_var_refs) {
-		ret = save_hist_vars(hist_data);
+		ret = tracing_map_init(hist_data->map);
 		if (ret)
-			goto out_unreg;
+			goto out_free;
 	}
 
-	ret = tracing_map_init(hist_data->map);
-	if (ret)
-		goto out_unreg;
-enable:
+	ret = event_trigger_register(cmd_ops, file, glob, trigger_data);
+	if (ret < 0)
+		goto out_free;
+
 	ret = hist_trigger_enable(trigger_data, file);
 	if (ret)
 		goto out_unreg;