linux-kernel - [PATCH v6 13/18] perf: Skip user unwind if the task is a kernel thread.

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Message-ID: <20250425145813.862449275@goodmis.org>
Date: Fri, 25 Apr 2025 10:54:35 -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>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Josh Poimboeuf <jpoimboe@...nel.org>,
 x86@...nel.org,
 Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...nel.org>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Indu Bhagat <indu.bhagat@...cle.com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>,
 Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 linux-perf-users@...r.kernel.org,
 Mark Brown <broonie@...nel.org>,
 linux-toolchains@...r.kernel.org,
 Jordan Rome <jordalgo@...a.com>,
 Sam James <sam@...too.org>,
 Andrii Nakryiko <andrii.nakryiko@...il.com>,
 Jens Remus <jremus@...ux.ibm.com>,
 Florian Weimer <fweimer@...hat.com>,
 Andy Lutomirski <luto@...nel.org>,
 Weinan Liu <wnliu@...gle.com>,
 Blake Jones <blakejones@...gle.com>,
 Beau Belgrave <beaub@...ux.microsoft.com>,
 "Jose E. Marchesi" <jemarch@....org>,
 Alexander Aring <aahringo@...hat.com>
Subject: [PATCH v6 13/18] 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>
---
Changes since v5: https://lore.kernel.org/20250424162633.216110813@goodmis.org

- Use current->flags & PF_KTHREAD instead of current->mm == NULL.
  (Peter Zijlstra)

 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 430dd158b1ee..ec9edf602974 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