linux-kernel - [PATCH v6 1/6] tracing: Do not bother getting user space stacktraces for kernel threads

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Message-ID: <20250828180356.546256287@kernel.org>
Date: Thu, 28 Aug 2025 14:03:01 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org,
 x86@...nel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Andrii Nakryiko <andrii@...nel.org>,
 Indu Bhagat <indu.bhagat@...cle.com>,
 "Jose E. Marchesi" <jemarch@....org>,
 Beau Belgrave <beaub@...ux.microsoft.com>,
 Jens Remus <jremus@...ux.ibm.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Florian Weimer <fweimer@...hat.com>,
 Sam James <sam@...too.org>,
 Kees Cook <kees@...nel.org>,
 "Carlos O'Donell" <codonell@...hat.com>
Subject: [PATCH v6 1/6] tracing: Do not bother getting user space stacktraces for kernel
 threads

From: Steven Rostedt <rostedt@...dmis.org>

If a user space stacktrace is requested when running a kernel thread, just
return, as there's no point trying to get the user space stacktrace as
there is no user space.

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
Changes since v5: https://lore.kernel.org/20250424192613.014380756@goodmis.org

- Also add check for PF_USER_WORKER to test for kernel thread

 kernel/trace/trace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1b7db732c0b1..2cca29c9863d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3138,6 +3138,10 @@ ftrace_trace_userstack(struct trace_array *tr,
 	if (!(tr->trace_flags & TRACE_ITER_USERSTACKTRACE))
 		return;

+	/* No point doing user space stacktraces on kernel threads */
+	if (current->flags & (PF_KTHREAD | PF_USER_WORKER))
+		return;
+
 	/*
 	 * NMIs can not handle page faults, even with fix ups.
 	 * The save user stack can (and often does) fault.
-- 
2.50.1