Commit a01fdc89 authored by Steven Rostedt (Google)'s avatar Steven Rostedt (Google)
Browse files

tracing: Add trace_trigger kernel command line option 

Allow triggers to be enabled at kernel boot up. For example:

  trace_trigger="sched_switch.stacktrace if prev_state == 2"

The above will enable the stacktrace trigger on top of the sched_switch
event and only trigger if its prev_state is 2 (TASK_UNINTERRUPTIBLE). Then
at boot up, a stacktrace will trigger and be recorded in the tracing ring
buffer every time the sched_switch happens where the previous state is
TASK_INTERRUPTIBLE.

Another useful trigger would be "traceoff" which can stop tracing on an
event if a field of the event matches a certain value defined by the
filter ("if" statement).

Link: https://lore.kernel.org/linux-trace-kernel/20221020210056.0d8d0a5b@gandalf.local.home



Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 8230f27b

Documentation/admin-guide/kernel-parameters.txt

+19 −0
Original line number Diff line number Diff line
@@ -6257,6 +6257,25 @@ 
			See also Documentation/trace/ftrace.rst "trace options"

			section.



	trace_trigger=[trigger-list]

			[FTRACE] Add a event trigger on specific events.

			Set a trigger on top of a specific event, with an optional

			filter.



			The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..."

			Where more than one trigger may be specified that are comma deliminated.



			For example:



			  trace_trigger="sched_switch.stacktrace if prev_state == 2"



			The above will enable the "stacktrace" trigger on the "sched_switch"

			event but only trigger it if the "prev_state" of the "sched_switch"

			event is "2" (TASK_UNINTERUPTIBLE).



			See also "Event triggers" in Documentation/trace/events.rst





	traceoff_on_warning

			[FTRACE] enable this option to disable tracing when a

			warning is hit. This turns off "tracing_on". Tracing can

kernel/trace/trace_events.c

+70 −2
Original line number Diff line number Diff line
@@ -2796,6 +2796,44 @@ trace_create_new_event(struct trace_event_call *call, 
	return file;

}



#ifdef CONFIG_HIST_TRIGGERS

#define MAX_BOOT_TRIGGERS 32



static struct boot_triggers {

	const char		*event;

	char			*trigger;

} bootup_triggers[MAX_BOOT_TRIGGERS];



static char bootup_trigger_buf[COMMAND_LINE_SIZE];

static int nr_boot_triggers;



static __init int setup_trace_triggers(char *str)

{

	char *trigger;

	char *buf;

	int i;



	strlcpy(bootup_trigger_buf, str, COMMAND_LINE_SIZE);

	ring_buffer_expanded = true;

	disable_tracing_selftest("running event triggers");



	buf = bootup_trigger_buf;

	for (i = 0; i < MAX_BOOT_TRIGGERS; i++) {

		trigger = strsep(&buf, ",");

		if (!trigger)

			break;

		bootup_triggers[i].event = strsep(&trigger, ".");

		bootup_triggers[i].trigger = strsep(&trigger, ".");

		if (!bootup_triggers[i].trigger)

			break;

	}



	nr_boot_triggers = i;

	return 1;

}

__setup("trace_trigger=", setup_trace_triggers);

#endif



/* Add an event to a trace directory */

static int

__trace_add_new_event(struct trace_event_call *call, struct trace_array *tr)
@@ -2812,6 +2850,28 @@ __trace_add_new_event(struct trace_event_call *call, struct trace_array *tr) 
		return event_define_fields(call);

}



#ifdef CONFIG_HIST_TRIGGERS

static void trace_early_triggers(struct trace_event_file *file, const char *name)

{

	int ret;

	int i;



	for (i = 0; i < nr_boot_triggers; i++) {

		if (strcmp(name, bootup_triggers[i].event))

			continue;

		mutex_lock(&event_mutex);

		ret = trigger_process_regex(file, bootup_triggers[i].trigger);

		mutex_unlock(&event_mutex);

		if (ret)

			pr_err("Failed to register trigger '%s' on event %s\n",

			       bootup_triggers[i].trigger,

			       bootup_triggers[i].event);

	}

}

#else

static inline void trace_early_triggers(struct trace_event_file *file, const char *name) { }

#endif



/*

 * Just create a descriptor for early init. A descriptor is required

 * for enabling events at boot. We want to enable events before
@@ -2822,12 +2882,19 @@ __trace_early_add_new_event(struct trace_event_call *call, 
			    struct trace_array *tr)

{

	struct trace_event_file *file;

	int ret;



	file = trace_create_new_event(call, tr);

	if (!file)

		return -ENOMEM;



	return event_define_fields(call);

	ret = event_define_fields(call);

	if (ret)

		return ret;



	trace_early_triggers(file, trace_event_name(call));



	return 0;

}



struct ftrace_module_file_ops;
@@ -3735,6 +3802,8 @@ static __init int event_trace_enable(void) 
			list_add(&call->list, &ftrace_events);

	}



	register_trigger_cmds();



	/*

	 * We need the top trace array to have a working set of trace

	 * points at early init, before the debug files and directories
@@ -3749,7 +3818,6 @@ static __init int event_trace_enable(void) 


	register_event_cmds();



	register_trigger_cmds();



	return 0;

}