[for-next][PATCH 03/11] tracing: Add trace_trigger kernel command line option

Steven Rostedt
2022-11-24T14:51:15Z

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

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: Steven Rostedt (Google) <rostedt@goodmis.org>
---
.../admin-guide/kernel-parameters.txt | 19 +++++
kernel/trace/trace_events.c | 72 ++++++++++++++++++-
2 files changed, 89 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a465d5242774..ccf91a4bf113 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -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
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index f71ea6e79b3c..3bfaf560ecc4 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -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;
}
--
2.35.1