linux-kernel - Re: [PATCH 1/3] task: Add a count of task rcu users

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Date:   Wed, 4 Sep 2019 16:36:33 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Christoph Lameter <cl@...ux.com>,
        Kirill Tkhai <tkhai@...dex.ru>, Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH 1/3] task: Add a count of task rcu users

On 09/02, Eric W. Biederman wrote:
>
> @@ -900,10 +900,9 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
> -	/*
> -	 * One for us, one for whoever does the "release_task()" (usually
> -	 * parent)
> -	 */
> +	/* One for the user space visible state that goes away when reaped. */
> +	refcount_set(&tsk->rcu_users, 1);

forgot to mention...

This is minor, but we don't really need to initialize child->rcu_users in
dup_task_struct(), we can just add

	.rcu_users = REFCOUNT_INIT(2),

into init_task's initializer.

Until we have a refcount_inc(task->rcu_users) user, of course.

Oleg.