Commit 288709c9 authored by Steven Rostedt (Google)'s avatar Steven Rostedt (Google)
Browse files

tracing: Allow stacktraces to be saved as histogram variables 

Allow to save stacktraces into a histogram variable. This will be used by
synthetic events to allow a stacktrace from one event to be passed and
displayed by another event.

The special keyword "stacktrace" is to be used to trigger a stack
trace for the event that the histogram trigger is attached to.

  echo 'hist:keys=pid:st=stacktrace" > events/sched/sched_waking/trigger

Currently nothing can get access to the "$st" variable above that contains
the stack trace, but that will soon change.

Link: https://lkml.kernel.org/r/20230117152235.856323729@goodmis.org



Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Ching-lin Yu <chinglinyu@google.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 19ff8049

kernel/trace/trace_events_hist.c

+42 −10
Original line number Diff line number Diff line
@@ -1360,6 +1360,8 @@ static const char *hist_field_name(struct hist_field *field, 
			field_name = field->name;

	} else if (field->flags & HIST_FIELD_FL_TIMESTAMP)

		field_name = "common_timestamp";

	else if (field->flags & HIST_FIELD_FL_STACKTRACE)

		field_name = "stacktrace";

	else if (field->flags & HIST_FIELD_FL_HITCOUNT)

		field_name = "hitcount";
@@ -1980,6 +1982,10 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data, 


	if (flags & HIST_FIELD_FL_STACKTRACE) {

		hist_field->fn_num = HIST_FIELD_FN_NOP;

		hist_field->size = HIST_STACKTRACE_SIZE;

		hist_field->type = kstrdup_const("unsigned long[]", GFP_KERNEL);

		if (!hist_field->type)

			goto free;

		goto out;

	}
@@ -2351,6 +2357,8 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file, 
		hist_data->enable_timestamps = true;

		if (*flags & HIST_FIELD_FL_TIMESTAMP_USECS)

			hist_data->attrs->ts_in_usecs = true;

	} else if (strcmp(field_name, "stacktrace") == 0) {

		*flags |= HIST_FIELD_FL_STACKTRACE;

	} else if (strcmp(field_name, "common_cpu") == 0)

		*flags |= HIST_FIELD_FL_CPU;

	else if (strcmp(field_name, "hitcount") == 0)
@@ -3119,13 +3127,24 @@ static inline void __update_field_vars(struct tracing_map_elt *elt, 
		var_val = hist_fn_call(val, elt, buffer, rbe, rec);

		var_idx = var->var.idx;



		if (val->flags & HIST_FIELD_FL_STRING) {

		if (val->flags & (HIST_FIELD_FL_STRING |

				  HIST_FIELD_FL_STACKTRACE)) {

			char *str = elt_data->field_var_str[j++];

			char *val_str = (char *)(uintptr_t)var_val;

			unsigned int size;



			if (val->flags & HIST_FIELD_FL_STRING) {

				size = min(val->size, STR_VAR_LEN_MAX);

				strscpy(str, val_str, size);

			} else {

				int e;



				e = stack_trace_save((void *)str,

						     HIST_STACKTRACE_DEPTH,

						     HIST_STACKTRACE_SKIP);

				if (e < HIST_STACKTRACE_DEPTH - 1)

					((unsigned long *)str)[e] = 0;

			}

			var_val = (u64)(uintptr_t)str;

		}

		tracing_map_set_var(elt, var_idx, var_val);
@@ -3824,7 +3843,8 @@ static void save_field_var(struct hist_trigger_data *hist_data, 
{

	hist_data->field_vars[hist_data->n_field_vars++] = field_var;



	if (field_var->val->flags & HIST_FIELD_FL_STRING)

	/* Stack traces are saved in the string storage too */

	if (field_var->val->flags & (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE))

		hist_data->n_field_var_str++;

}
@@ -4103,7 +4123,8 @@ static int action_create(struct hist_trigger_data *hist_data, 
			}



			hist_data->save_vars[hist_data->n_save_vars++] = field_var;

			if (field_var->val->flags & HIST_FIELD_FL_STRING)

			if (field_var->val->flags &

			    (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE))

				hist_data->n_save_var_str++;

			kfree(param);

		}
@@ -4351,7 +4372,8 @@ static int create_var_field(struct hist_trigger_data *hist_data, 
	if (!ret && hist_data->fields[val_idx]->flags & HIST_FIELD_FL_EXECNAME)

		update_var_execname(hist_data->fields[val_idx]);



	if (!ret && hist_data->fields[val_idx]->flags & HIST_FIELD_FL_STRING)

	if (!ret && hist_data->fields[val_idx]->flags &

	    (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE))

		hist_data->fields[val_idx]->var_str_idx = hist_data->n_var_str++;



	return ret;
@@ -5092,7 +5114,8 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data, 
		if (hist_field->flags & HIST_FIELD_FL_VAR) {

			var_idx = hist_field->var.idx;



			if (hist_field->flags & HIST_FIELD_FL_STRING) {

			if (hist_field->flags &

			    (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE)) {

				unsigned int str_start, var_str_idx, idx;

				char *str, *val_str;

				unsigned int size;
@@ -5105,9 +5128,18 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data, 
				str = elt_data->field_var_str[idx];

				val_str = (char *)(uintptr_t)hist_val;



				if (hist_field->flags & HIST_FIELD_FL_STRING) {

					size = min(hist_field->size, STR_VAR_LEN_MAX);

					strscpy(str, val_str, size);

				} else {

					int e;



					e = stack_trace_save((void *)str,

							     HIST_STACKTRACE_DEPTH,

							     HIST_STACKTRACE_SKIP);

					if (e < HIST_STACKTRACE_DEPTH - 1)

						((unsigned long *)str)[e] = 0;

				}

				hist_val = (u64)(uintptr_t)str;

			}

			tracing_map_set_var(elt, var_idx, hist_val);