Re: [RFC][PATCH 2/2] treewide: Have the task->flags & PF_KTHREAD check use the helper functions

Alexei Starovoitov
2025-04-26T03:23:12Z

On Fri, Apr 25, 2025 at 4:10 PM Kees Cook <kees@kernel.org> wrote:
>
> On Fri, Apr 25, 2025 at 04:41:22PM -0400, Steven Rostedt wrote:
> > From: Steven Rostedt <rostedt@goodmis.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.