linux-kernel - Re: [PATCH/RFC] core/nfsd: allow kernel threads to use task

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Message-ID: <20231128165945.GD22743@redhat.com>
Date:   Tue, 28 Nov 2023 17:59:45 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <brauner@...nel.org>
Cc:     NeilBrown <neilb@...e.de>, Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Chuck Lever <chuck.lever@...cle.com>,
        Jeff Layton <jlayton@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nfs@...r.kernel.org
Subject: Re: [PATCH/RFC] core/nfsd: allow kernel threads to use task_work.

On 11/28, Christian Brauner wrote:
>
> Yeah, I had played with that as well. Only reason I didn't do it was to
> avoid a PF_* flag. If that's preferable it might be worth to just add
> PF_TASK_WORK and decouple this from PF_KTHREAD.

OK, I won't insist.

But,

> +       /*
> +        * By default only non-kernel threads can use task work. Kernel
> +        * threads that manage task work explicitly can add that flag in
> +        * their kthread callback.
> +        */
> +       if (!args->kthread)
> +               p->flags |= PF_TASK_WORK;

The comment and the name of the new flag look a bit misleading to me...

kthreads can use task_work's. You can create a kthread which does
task_work_run() from time to time and use task_work_add() on it,
nothing wrong with that.

Probably nobody does this right now (I didn't try to check), but please
note irq_thread()->task_work_add(on_exit_work).

Oleg.