linux-kernel - [RFC][PATCH 1/2] kthread: Add is_user_thread() and is_kernel

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Message-ID: <20250425204313.616425861@goodmis.org>
Date: Fri, 25 Apr 2025 16:41:21 -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>,
 Peter Zijlstra <peterz@...radead.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Ingo Molnar <mingo@...hat.com>,
 x86@...nel.org,
 Kees Cook <kees@...nel.org>,
 bpf@...r.kernel.org,
 Tejun Heo <tj@...nel.org>,
 Julia Lawall <Julia.Lawall@...ia.fr>,
 Nicolas Palix <nicolas.palix@...g.fr>,
 cocci@...ia.fr
Subject: [RFC][PATCH 1/2] kthread: Add is_user_thread() and is_kernel_thread() helper functions

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

In order to know if a task is a user thread or a kernel thread it is
recommended to test the task flags for PF_KTHREAD. The old way was to
check if the task mm pointer is NULL.

It is an easy mistake to not test the flag correctly, as:

	if (!(task->flag & PF_KTHREAD))

Is not immediately obvious that it's testing for a user thread.

Add helper functions:

  is_user_thread()
  is_kernel_thread()

that can make seeing what is being tested for much more obvious:

	if (is_user_thread(task))

Link: https://lore.kernel.org/all/20250425133416.63d3e3b8@gandalf.local.home/

Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 include/linux/sched.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac1982893..823f38b0fd3e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1785,6 +1785,16 @@ static __always_inline bool is_percpu_thread(void)
 #endif
 }
 
+static __always_inline bool is_user_thread(struct task_struct *task)
+{
+	return !(task->flags & PF_KTHREAD);
+}
+
+static __always_inline bool is_kernel_thread(struct task_struct *task)
+{
+	return task->flags & PF_KTHREAD;
+}
+
 /* Per-process atomic flags. */
 #define PFA_NO_NEW_PRIVS		0	/* May not gain new privileges. */
 #define PFA_SPREAD_PAGE			1	/* Spread page cache over cpuset */
-- 
2.47.2