linux-kernel - [PATCH v7 17/17] perf: Skip user unwind if the task is a kernel thread.

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Message-ID: <20250502165010.249866358@goodmis.org>
Date: Fri, 02 May 2025 12:48:03 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 x86@...nel.org,
 Jiri Olsa <jolsa@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>
Subject: [PATCH v7 17/17] perf: Skip user unwind if the task is a kernel thread.

From: Josh Poimboeuf <jpoimboe@...nel.org>

If the task is not a user thread, there's no user stack to unwind.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/events/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7c7d5a27c568..02e52df7a02e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8101,7 +8101,8 @@ struct perf_callchain_entry *
 perf_callchain(struct perf_event *event, struct pt_regs *regs)
 {
 	bool kernel = !event->attr.exclude_callchain_kernel;
-	bool user   = !event->attr.exclude_callchain_user;
+	bool user   = !event->attr.exclude_callchain_user &&
+		!(current->flags & PF_KTHREAD);
 	/* Disallow cross-task user callchains. */
 	bool crosstask = event->ctx->task && event->ctx->task != current;
 	const u32 max_stack = event->attr.sample_max_stack;
-- 
2.47.2