Re: [PATCH 1/1] tracing: fix a WARN from trace_event_dyn_put_ref

Steven Rostedt
2022-08-16T19:24:14Z

On Tue, 16 Aug 2022 11:54:18 -0700
Krister Johansen <kjlx@templeofstupid.com> wrote:

> What do you think, would either of these be a solution that you would
> find acceptable?

Actually, I think the issue is that the unreg() calls trace_event_put_ref()
but the reg() does not do the try_get_ref(), but the perf_trace_init()
does. Which is the broken symmetry.

I think if we pull out the trace_event_put_ref() from the unreg() function,
we fix the bug and also put back the symmetry.

Does this patch work?

[ Untested, and not even compiled ]

-- Steve

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index a114549720d6..61e3a2620fa3 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -157,7 +157,7 @@ static void perf_trace_event_unreg(struct perf_event *p_event)
int i;

if (--tp_event->perf_refcount > 0)
- goto out;
+ return;

tp_event->class->reg(tp_event, TRACE_REG_PERF_UNREGISTER, NULL);

@@ -176,8 +176,6 @@ static void perf_trace_event_unreg(struct perf_event *p_event)
perf_trace_buf[i] = NULL;
}
}
-out:
- trace_event_put_ref(tp_event);
}

static int perf_trace_event_open(struct perf_event *p_event)
@@ -241,6 +239,7 @@ void perf_trace_destroy(struct perf_event *p_event)
mutex_lock(&event_mutex);
perf_trace_event_close(p_event);
perf_trace_event_unreg(p_event);
+ trace_event_put_ref(p_event->tp_event);
mutex_unlock(&event_mutex);
}

@@ -292,6 +291,7 @@ void perf_kprobe_destroy(struct perf_event *p_event)
mutex_lock(&event_mutex);
perf_trace_event_close(p_event);
perf_trace_event_unreg(p_event);
+ trace_event_put_ref(p_event->tp_event);
mutex_unlock(&event_mutex);

destroy_local_trace_kprobe(p_event->tp_event);
@@ -347,6 +347,7 @@ void perf_uprobe_destroy(struct perf_event *p_event)
mutex_lock(&event_mutex);
perf_trace_event_close(p_event);
perf_trace_event_unreg(p_event);
+ trace_event_put_ref(p_event->tp_event);
mutex_unlock(&event_mutex);
destroy_local_trace_uprobe(p_event->tp_event);
}