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

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Date:   Tue, 28 Nov 2023 14:52:59 +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:
>
> Should be simpler if you invert the logic?
>
> COMPLETELY UNTESTED

Agreed, this looks much better to me. But perhaps we can just add the new
PF_KTHREAD_XXX flag and change fput


	--- a/fs/file_table.c
	+++ b/fs/file_table.c
	@@ -445,7 +445,8 @@ void fput(struct file *file)
		if (atomic_long_dec_and_test(&file->f_count)) {
			struct task_struct *task = current;
	 
	-		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
	+		if (likely(!in_interrupt() &&
	+		    task->flags & (PF_KTHREAD|PF_KTHREAD_XXX) != PF_KTHREAD) {
				init_task_work(&file->f_rcuhead, ____fput);
				if (!task_work_add(task, &file->f_rcuhead, TWA_RESUME))
					return;

?

Then nfsd() can simply set PF_KTHREAD_XXX. This looks even simpler to me.

Oleg.