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tracing: Add trace_trigger kernel command line option

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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>
This commit is contained in:
Steven Rostedt (Google) 2022-10-20 21:00:56 -04:00
parent 8230f27b1c
commit a01fdc897f
2 changed files with 89 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

19
Documentation/admin-guide/kernel-parameters.txt
View file

@ -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

72
kernel/trace/trace_events.c
View file

@ -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;
}