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Date:   Tue, 16 Aug 2022 19:28:17 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     Jiri Olsa <jolsa@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        David Reaver <me@davidreaver.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Krister Johansen <kjlx@templeofstupid.com>
Subject: [PATCH] tracing/perf: Fix double put of trace event when init fails
Message-ID: <20220816192817.43d5e17f@gandalf.local.home>
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From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

If in perf_trace_event_init(), the perf_trace_event_open() fails, then it
will call perf_trace_event_unreg() which will not only unregister the perf
trace event, but will also call the put() function of the tp_event.

The problem here is that the trace_event_try_get_ref() is called by the
caller of perf_trace_event_init() and if perf_trace_event_init() returns a
failure, it will then call trace_event_put(). But since the
perf_trace_event_unreg() already called the trace_event_put() function, it
triggers a WARN_ON().

 WARNING: CPU: 1 PID: 30309 at kernel/trace/trace_dynevent.c:46 trace_event_dyn_put_ref+0x15/0x20

If perf_trace_event_reg() does not call the trace_event_try_get_ref() then
the perf_trace_event_unreg() should not be calling trace_event_put(). This
breaks symmetry and causes bugs like these.

Pull out the trace_event_put() from perf_trace_event_unreg() and call it
in the locations that perf_trace_event_unreg() is called. This not only
fixes this bug, but also brings back the proper symmetry of the reg/unreg
vs get/put logic.

Link: https://lore.kernel.org/all/cover.1660347763.git.kjlx@templeofstupid.com/

Reported-by: Krister Johansen <kjlx@templeofstupid.com>
Reviewed-by: Krister Johansen <kjlx@templeofstupid.com>
Tested-by: Krister Johansen <kjlx@templeofstupid.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_event_perf.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

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);
 }
-- 
2.35.1