linux-kernel - Re: [PATCH 3/3] task: Clean house now that tasks on the runqueue are rcu protected

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Message-ID: <20190903130606.GA17626@redhat.com>
Date:   Tue, 3 Sep 2019 15:06:06 +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 3/3] task: Clean house now that tasks on the runqueue are
 rcu protected

On 09/02, Eric W. Biederman wrote:
>
> @@ -1644,7 +1644,7 @@ static void task_numa_compare(struct task_numa_env *env,
>  		return;
>  
>  	rcu_read_lock();
> -	cur = task_rcu_dereference(&dst_rq->curr);
> +	cur = rcu_dereference(dst_rq->curr);
>  	if (cur && ((cur->flags & PF_EXITING) || is_idle_task(cur)))
>  		cur = NULL;

afaics rq->curr can't be NULL, so you can also simplify the "if" check

	cur = task_rcu_dereference(&dst_rq->curr);
	if ((cur->flags & PF_EXITING) || is_idle_task(cur))
		cur = NULL;

Same for membarrier_global_expedited/membarrier_private_expedited changed
by this patch.

Oleg.