From: Steven Rostedt (Google) <rostedt@goodmis.org>
Date: Fri, 23 Feb 2024 01:33:25 +0000 (-0500)
Subject: tracing: Decrement the snapshot if the snapshot trigger fails to register
X-Git-Tag: v6.9-rc1~64^2~10
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=2048fdc27525c6b32c63f8429d9335b7fd2f90c2;p=thirdparty%2Fkernel%2Flinux.git

tracing: Decrement the snapshot if the snapshot trigger fails to register

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.

Link: https://lore.kernel.org/linux-trace-kernel/20240223013344.729055907@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vincent Donnefort <vdonnefort@google.com>
Fixes: 16f7e48ffc53a ("tracing: Add snapshot refcount")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---

diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 62e4f58b8671b..4bec043c8690d 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,