linux-kernel - Re: [PATCH v10 0/2] kernel/fork: beware of __put_task

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Date:   Mon, 19 Jun 2023 13:07:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Wander Lairson Costa <wander@...hat.com>
Cc:     "Christian Brauner (Microsoft)" <brauner@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Mike Christie <michael.christie@...cle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Oleg Nesterov <oleg@...hat.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>,
        Andrei Vagin <avagin@...il.com>,
        Nicholas Piggin <npiggin@...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>,
        Luis Goncalves <lgoncalv@...hat.com>
Subject: Re: [PATCH v10 0/2] kernel/fork: beware of __put_task_struct calling
 context

On Wed, Jun 14, 2023 at 09:23:20AM -0300, Wander Lairson Costa wrote:
> Under PREEMPT_RT, __put_task_struct() indirectly acquires sleeping
> locks. Therefore, it can't be called from an non-preemptible context.
> 
> Instead of calling __put_task_struct() directly, we defer it using
> call_rcu(). A more natural approach would use a workqueue, but since
> in PREEMPT_RT, we can't allocate dynamic memory from atomic context,
> the code would become more complex because we would need to put the
> work_struct instance in the task_struct and initialize it when we
> allocate a new task_struct.

> 
> Wander Lairson Costa (2):
>   kernel/fork: beware of __put_task_struct calling context
>   sched: avoid false lockdep splat in put_task_struct()

Thanks!