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

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Message-ID: <20250426083634.25897a33@batman.local.home>
Date: Sat, 26 Apr 2025 08:36:34 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Kees Cook <kees@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 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, 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: Re: [RFC][PATCH 1/2] kthread: Add is_user_thread() and
 is_kernel_thread() helper functions

On Fri, 25 Apr 2025 16:03:16 -0700
Kees Cook <kees@...nel.org> wrote:

> > +static __always_inline bool is_kernel_thread(struct task_struct *task)
> > +{
> > +	return task->flags & PF_KTHREAD;  
> 
> nit: maybe do explicit type conversion:
> 
> 	return !!(task->flags & PF_KTHREAD);
> 
> but that's just a style issue, really.

I may use Boris's suggestion (which I thought of doing originally too)
and have this return:

	return !is_user_thread(task);


> 
> Reviewed-by: Kees Cook <kees@...nel.org>

Thanks.

> 
> Thank you for not using current->mm -- KUnit, live patching, etc, all
> use current->mm but are kthreads. :)

Yeah, Peter was stressing this.

-- Steve