linux-kernel - Re: [RFC PATCH 3/3] rseq: extend struct rseq with numa node id

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Message-ID: <YgBDDVZSZqID8L3R@hirez.programming.kicks-ass.net>
Date:   Sun, 6 Feb 2022 22:52:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>,
        Florian Weimer <fw@...eb.enyo.de>, David.Laight@...lab.com,
        carlos@...hat.com, Peter Oskolkov <posk@...k.io>,
        libc-coord@...ts.openwall.com
Subject: Re: [RFC PATCH 3/3] rseq: extend struct rseq with numa node id

On Thu, Feb 03, 2022 at 02:38:53PM -0500, Mathieu Desnoyers wrote:
> +static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
>  {
> -	u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED;
> +	u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED, node_id = 0;
>  
>  	/*
>  	 * Reset cpu_id_start to its initial state (0).
> @@ -124,6 +126,11 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t)
>  	 */
>  	if (put_user(cpu_id, &t->rseq->cpu_id))
>  		return -EFAULT;
> +	/*
> +	 * Reset node_id to its initial state (0).
> +	 */
> +	if (put_user(node_id, &t->rseq->node_id))
> +		return -EFAULT;

Why 0 vs -1 ?