linux-kernel - [PATCH v2] tracing: Skip update_last_data() if cleared and remove active check for save

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Message-ID: <174165660328.1173316.15529357882704817499.stgit@devnote2>
Date: Tue, 11 Mar 2025 10:30:03 +0900
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [PATCH v2] tracing: Skip update_last_data() if cleared and remove active check for save_mod()

From: Masami Hiramatsu (Google) <mhiramat@...nel.org>

If the last boot data is already cleared, there is no reason to update it
again. Skip if the TRACE_ARRAY_FL_LAST_BOOT is cleared.
Also, for calling save_mod() when module loading, we don't need to check
the trace is active or not because any module address can be on the
stacktrace.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
 Changes in v2:
  - merge [1/3] and [2/3] in the previous series.
---
 kernel/trace/trace.c |   26 ++++++++------------------
 1 file changed, 8 insertions(+), 18 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c3c79908766e..d17278a72e72 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6033,6 +6033,12 @@ static void update_last_data(struct trace_array *tr)
 	if (!(tr->flags & TRACE_ARRAY_FL_BOOT))
 		return;
 
+	if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
+		return;
+
+	/* Only if the buffer has previous boot data clear and update it. */
+	tr->flags &= ~TRACE_ARRAY_FL_LAST_BOOT;
+
 	/* Reset the module list and reload them */
 	if (tr->scratch) {
 		struct trace_scratch *tscratch = tr->scratch;
@@ -6045,9 +6051,6 @@ static void update_last_data(struct trace_array *tr)
 		module_for_each_mod(save_mod, tr);
 	}
 
-	if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
-		return;
-
 	/*
 	 * Need to clear all CPU buffers as there cannot be events
 	 * from the previous boot mixed with events with this boot
@@ -6070,7 +6073,6 @@ static void update_last_data(struct trace_array *tr)
 #else
 	tscratch->kaslr_addr = 0;
 #endif
-	tr->flags &= ~TRACE_ARRAY_FL_LAST_BOOT;
 }
 
 /**
@@ -10092,15 +10094,6 @@ static void trace_module_remove_evals(struct module *mod)
 static inline void trace_module_remove_evals(struct module *mod) { }
 #endif /* CONFIG_TRACE_EVAL_MAP_FILE */
 
-static bool trace_array_active(struct trace_array *tr)
-{
-	if (tr->current_trace != &nop_trace)
-		return true;
-
-	/* 0 is no events, 1 is all disabled */
-	return trace_events_enabled(tr, NULL) > 1;
-}
-
 static void trace_module_record(struct module *mod)
 {
 	struct trace_array *tr;
@@ -10109,11 +10102,8 @@ static void trace_module_record(struct module *mod)
 		/* Update any persistent trace array that has already been started */
 		if ((tr->flags & (TRACE_ARRAY_FL_BOOT | TRACE_ARRAY_FL_LAST_BOOT)) ==
 		    TRACE_ARRAY_FL_BOOT) {
-			/* Only update if the trace array is active */
-			if (trace_array_active(tr)) {
-				guard(mutex)(&scratch_mutex);
-				save_mod(mod, tr);
-			}
+			guard(mutex)(&scratch_mutex);
+			save_mod(mod, tr);
 		}
 	}
 }