linux-kernel - [PATCH] tracing: Do not synchronize freeing of trigger filter on boot up

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Message-ID: <20221213172429.7774f4ba@gandalf.local.home>
Date:   Tue, 13 Dec 2022 17:24:29 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] tracing: Do not synchronize freeing of trigger filter on
 boot up

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

If a trigger filter on the kernel command line fails to apply (due to
syntax error), it will be freed. The freeing will call
tracepoint_synchronize_unregister(), but this is not needed during early
boot up, and will even trigger a lockdep splat.

Avoid calling the synchronization function when system_state is
SYSTEM_BOOTING.

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/trace_events_trigger.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 19ce9d22bfd7..e535959939d3 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1085,8 +1085,14 @@ int set_trigger_filter(char *filter_str,
 	rcu_assign_pointer(data->filter, filter);
 
 	if (tmp) {
-		/* Make sure the call is done with the filter */
-		tracepoint_synchronize_unregister();
+		/*
+		 * Make sure the call is done with the filter.
+		 * It is possible that a filter could fail at boot up,
+		 * and then this path will be called. Avoid the synchronization
+		 * in that case.
+		 */
+		if (system_state != SYSTEM_BOOTING)
+			tracepoint_synchronize_unregister();
 		free_event_filter(tmp);
 	}
 
-- 
2.35.1