linux-kernel - [PATCH 2/2] tracing: Decrement the snapshot if the snapshot trigger fails to register

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Message-ID: <20240223013344.729055907@goodmis.org>
Date: Thu, 22 Feb 2024 20:33:25 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Vincent Donnefort <vdonnefort@...gle.com>
Subject: [PATCH 2/2] tracing: Decrement the snapshot if the snapshot trigger fails to
 register

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

Running the ftrace selftests caused the ring buffer mapping test to fail.
Investigating, I found that the snapshot counter would be incremented
every time a snapshot trigger was added, even if that snapshot trigger
failed.

 # cd /sys/kernel/tracing
 # echo "snapshot" > events/sched/sched_process_fork/trigger
 # echo "snapshot" > events/sched/sched_process_fork/trigger
 -bash: echo: write error: File exists

That second one that fails increments the snapshot counter but doesn't
decrement it. It needs to be decremented when the snapshot fails.

Fixes: 16f7e48ffc53a ("tracing: Add snapshot refcount")
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_events_trigger.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 62e4f58b8671..4bec043c8690 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1491,7 +1491,10 @@ register_snapshot_trigger(char *glob,
 	if (ret < 0)
 		return ret;
 
-	return register_trigger(glob, data, file);
+	ret = register_trigger(glob, data, file);
+	if (ret < 0)
+		tracing_disarm_snapshot(file->tr);
+	return ret;
 }
 
 static void unregister_snapshot_trigger(char *glob,
-- 
2.43.0