linux-kernel - Re: [PATCH v8] kernel/fork: beware of __put_task

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Message-ID: <CAAq0SUkHDf6Tnhrc5ys4rOGWtepFfdv3=d6GiA=BB7yvDUj8vw@mail.gmail.com>
Date:   Mon, 15 May 2023 14:14:12 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     "Christian Brauner (Microsoft)" <brauner@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Mike Christie <michael.christie@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Guo Ren <guoren@...nel.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        Hu Chunyu <chuhu@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Paul McKenney <paulmck@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v8] kernel/fork: beware of __put_task_struct calling context

On Mon, May 15, 2023 at 1:43 PM Oleg Nesterov <oleg@...hat.com> wrote:
>
> Certainly I have missed something...
>
> but,
>
> On 05/15, Wander Lairson Costa wrote:
> >
> > -extern void __put_task_struct(struct task_struct *t);
> > +extern void ___put_task_struct(struct task_struct *t);
> > +extern void __put_task_struct_rcu_cb(struct rcu_head *rhp);
>
> I don't understand these renames, why can't you simply put this fix
> into put_task_struct() ?
>

No particular reason, it was just a matter of style and keep the parts simple.

> but this is minor,
>
> > +static inline void __put_task_struct(struct task_struct *tsk)
> > +{
> ...
> > +     if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible())
> > +             call_rcu(&tsk->rcu, __put_task_struct_rcu_cb);
> > +     else
> > +             ___put_task_struct(tsk);
> > +}
>
> did you see the emails from Peter? In particular, this one:
>
>         https://lore.kernel.org/lkml/20230505133902.GC38236@hirez.programming.kicks-ass.net/
>

I didn't notice the lock_acquire/lock_release part. However, I tested
the patch with CONFIG_PROVE_RAW_LOCK_NESTING and there was no warning.

> Oleg.
>