[RFC][PATCH 1/2] kthread: Add is_user_thread() and is_kernel_thread() helper functions

Steven Rostedt
2025-04-25T20:41:15Z

From: Steven Rostedt <rostedt@goodmis.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@goodmis.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