linux-kernel - [PATCH 5/5] perf: Skip user unwind if the task is a kernel thread

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Message-ID: <20250717173333.809101137@kernel.org>
Date: Thu, 17 Jul 2025 13:31:30 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org,
 linux-perf-users@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>,
 Jens Axboe <axboe@...nel.dk>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 5/5] 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 1fa554e2666d..bd0a33f389d2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8166,7 +8166,8 @@ 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 | PF_USER_WORKER));
 	/* 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