linux-kernel - Re: [RFC][PATCH 2/2] treewide: Have the task->flags & PF

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Message-ID: <CAADnVQKdWSuDm52GmNor75rFZGNBLcoCto3oecA3D3QHD_MyCQ@mail.gmail.com>
Date: Fri, 25 Apr 2025 20:22:59 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Kees Cook <kees@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <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 ML <x86@...nel.org>, bpf <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 2/2] treewide: Have the task->flags & PF_KTHREAD
 check use the helper functions

On Fri, Apr 25, 2025 at 4:10 PM Kees Cook <kees@...nel.org> wrote:
>
> On Fri, Apr 25, 2025 at 04:41:22PM -0400, Steven Rostedt wrote:
> > From: Steven Rostedt <rostedt@...dmis.org>
> >
> > Getting the check if a task is a kernel thread or a user thread can be
> > error prone as it's not easy to see the difference.
> >
> >       if (!(task->flags & PF_KTHREAD))
> >
> > Is not immediately obvious that it's checking for a user thread.
> >
> >       if (is_user_thread(task))
> >
> > Is much easier to review, as it is obvious that it is checking if the task
> > is a user thread.
> >
> > Using a coccinelle script, convert these checks over to using either
> > is_user_thread() or is_kernel_thread().
> >
> >   $ cat kthread.cocci
> >   @@
> >   identifier task;
> >   @@
> >   -   !(task->flags & PF_KTHREAD)
> >   +   is_user_thread(task)
> >   @@
> >   identifier task;
> >   @@
> >   -   (task->flags & PF_KTHREAD) == 0
> >   +   is_user_thread(task)
> >   @@
> >   identifier task;
> >   @@
> >   -   (task->flags & PF_KTHREAD) != 0
> >   +   is_kernel_thread(task)
> >   @@
> >   identifier task;
> >   @@
> >   -   task->flags & PF_KTHREAD
> >   +   is_kernel_thread(task)
> >
> >   $ spatch --dir --include-headers kthread.cocci . > /tmp/t.patch
> >   $ patch -p1 < /tmp/t.patch
> >
> > Make sure to undo the conversion of the helper functions themselves!
> >
> >   $ git show include/linux/sched.h | patch -p1 -R
>
> FYI, the "file in" test can be helpful. I use it to exclude tools and
> samples regularly, and *I think* it would work for excluding individual
> files too:
>
> @name_of_rule depends !(file in "tools") && !(file in "samples")@
>
> I've been collecting random notes like this here:
>
> https://github.com/kees/kernel-tools/tree/trunk/coccinelle
>
> >  tools/sched_ext/scx_central.bpf.c          |  2 +-
> >  tools/sched_ext/scx_flatcg.bpf.c           |  2 +-
> >  tools/sched_ext/scx_qmap.bpf.c             |  2 +-
>
> I think these are fine. The Makefile is pulling in standard kbuild
> Makefiles, so I think the correct include directories (outside of
> tools/) are being used.

I suspect they are not fine.
I don't think they #include linux/sched.h
I would drop them for now.

Tejun,
please double check.