Commit fc800a10 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)
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tracing: Lock event_mutex before synth_event_mutex 

synthetic event is using synth_event_mutex for protecting
synth_event_list, and event_trigger_write() path acquires
locks as below order.

event_trigger_write(event_mutex)
  ->trigger_process_regex(trigger_cmd_mutex)
    ->event_hist_trigger_func(synth_event_mutex)

On the other hand, synthetic event creation and deletion paths
call trace_add_event_call() and trace_remove_event_call()
which acquires event_mutex. In that case, if we keep the
synth_event_mutex locked while registering/unregistering synthetic
events, its dependency will be inversed.

To avoid this issue, current synthetic event is using a 2 phase
process to create/delete events. For example, it searches existing
events under synth_event_mutex to check for event-name conflicts, and
unlocks synth_event_mutex, then registers a new event under event_mutex
locked. Finally, it locks synth_event_mutex and tries to add the
new event to the list. But it can introduce complexity and a chance
for name conflicts.

To solve this simpler, this introduces trace_add_event_call_nolock()
and trace_remove_event_call_nolock() which don't acquire
event_mutex inside. synthetic event can lock event_mutex before
synth_event_mutex to solve the lock dependency issue simpler.

Link: http://lkml.kernel.org/r/154140844377.17322.13781091165954002713.stgit@devbox



Reviewed-by: default avatarTom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: default avatarTom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 547cd9ea

include/linux/trace_events.h

+2 −0
Original line number Diff line number Diff line
@@ -529,6 +529,8 @@ extern int trace_event_raw_init(struct trace_event_call *call); 
extern int trace_define_field(struct trace_event_call *call, const char *type,

			      const char *name, int offset, int size,

			      int is_signed, int filter_type);

extern int trace_add_event_call_nolock(struct trace_event_call *call);

extern int trace_remove_event_call_nolock(struct trace_event_call *call);

extern int trace_add_event_call(struct trace_event_call *call);

extern int trace_remove_event_call(struct trace_event_call *call);

extern int trace_event_get_offsets(struct trace_event_call *call);

kernel/trace/trace_events.c

+28 −6
Original line number Diff line number Diff line
@@ -2305,11 +2305,11 @@ __trace_early_add_new_event(struct trace_event_call *call, 
struct ftrace_module_file_ops;

static void __add_event_to_tracers(struct trace_event_call *call);



/* Add an additional event_call dynamically */

int trace_add_event_call(struct trace_event_call *call)

int trace_add_event_call_nolock(struct trace_event_call *call)

{

	int ret;

	mutex_lock(&event_mutex);

	lockdep_assert_held(&event_mutex);



	mutex_lock(&trace_types_lock);



	ret = __register_event(call, NULL);
@@ -2317,6 +2317,16 @@ int trace_add_event_call(struct trace_event_call *call) 
		__add_event_to_tracers(call);



	mutex_unlock(&trace_types_lock);

	return ret;

}



/* Add an additional event_call dynamically */

int trace_add_event_call(struct trace_event_call *call)

{

	int ret;



	mutex_lock(&event_mutex);

	ret = trace_add_event_call_nolock(call);

	mutex_unlock(&event_mutex);

	return ret;

}
@@ -2366,17 +2376,29 @@ static int probe_remove_event_call(struct trace_event_call *call) 
	return 0;

}



/* Remove an event_call */

int trace_remove_event_call(struct trace_event_call *call)

/* no event_mutex version */

int trace_remove_event_call_nolock(struct trace_event_call *call)

{

	int ret;



	mutex_lock(&event_mutex);

	lockdep_assert_held(&event_mutex);



	mutex_lock(&trace_types_lock);

	down_write(&trace_event_sem);

	ret = probe_remove_event_call(call);

	up_write(&trace_event_sem);

	mutex_unlock(&trace_types_lock);



	return ret;

}



/* Remove an event_call */

int trace_remove_event_call(struct trace_event_call *call)

{

	int ret;



	mutex_lock(&event_mutex);

	ret = trace_remove_event_call_nolock(call);

	mutex_unlock(&event_mutex);



	return ret;

kernel/trace/trace_events_hist.c

+10 −14
Original line number Diff line number Diff line
@@ -912,7 +912,7 @@ static int register_synth_event(struct synth_event *event) 
	call->data = event;

	call->tp = event->tp;



	ret = trace_add_event_call(call);

	ret = trace_add_event_call_nolock(call);

	if (ret) {

		pr_warn("Failed to register synthetic event: %s\n",

			trace_event_name(call));
@@ -936,7 +936,7 @@ static int unregister_synth_event(struct synth_event *event) 
	struct trace_event_call *call = &event->call;

	int ret;



	ret = trace_remove_event_call(call);

	ret = trace_remove_event_call_nolock(call);



	return ret;

}
@@ -1013,12 +1013,10 @@ static void add_or_delete_synth_event(struct synth_event *event, int delete) 
	if (delete)

		free_synth_event(event);

	else {

		mutex_lock(&synth_event_mutex);

		if (!find_synth_event(event->name))

			list_add(&event->list, &synth_event_list);

		else

			free_synth_event(event);

		mutex_unlock(&synth_event_mutex);

	}

}
@@ -1030,6 +1028,7 @@ static int create_synth_event(int argc, char **argv) 
	int i, consumed = 0, n_fields = 0, ret = 0;

	char *name;



	mutex_lock(&event_mutex);

	mutex_lock(&synth_event_mutex);



	/*
@@ -1102,8 +1101,6 @@ static int create_synth_event(int argc, char **argv) 
		goto err;

	}

 out:

	mutex_unlock(&synth_event_mutex);



	if (event) {

		if (delete_event) {

			ret = unregister_synth_event(event);
@@ -1113,10 +1110,13 @@ static int create_synth_event(int argc, char **argv) 
			add_or_delete_synth_event(event, ret);

		}

	}

	mutex_unlock(&synth_event_mutex);

	mutex_unlock(&event_mutex);



	return ret;

 err:

	mutex_unlock(&synth_event_mutex);

	mutex_unlock(&event_mutex);



	for (i = 0; i < n_fields; i++)

		free_synth_field(fields[i]);
@@ -1127,12 +1127,10 @@ static int create_synth_event(int argc, char **argv) 


static int release_all_synth_events(void)

{

	struct list_head release_events;

	struct synth_event *event, *e;

	int ret = 0;



	INIT_LIST_HEAD(&release_events);



	mutex_lock(&event_mutex);

	mutex_lock(&synth_event_mutex);



	list_for_each_entry(event, &synth_event_list, list) {
@@ -1142,16 +1140,14 @@ static int release_all_synth_events(void) 
		}

	}



	list_splice_init(&event->list, &release_events);



	mutex_unlock(&synth_event_mutex);



	list_for_each_entry_safe(event, e, &release_events, list) {

	list_for_each_entry_safe(event, e, &synth_event_list, list) {

		list_del(&event->list);



		ret = unregister_synth_event(event);

		add_or_delete_synth_event(event, !ret);

	}

	mutex_unlock(&synth_event_mutex);

	mutex_unlock(&event_mutex);



	return ret;

}

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