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tracing: Lock event_mutex before synth_event_mutex

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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: Tom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Masami Hiramatsu
2018-11-05 18:00:43 +09:00
committed by Steven Rostedt (VMware)
parent 547cd9eacd
commit fc800a10be
3 changed files with 42 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
kernel/trace/trace_events_hist.c
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@@ -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;
}