linux-kernel - Re: [PATCH v5 2/4] rcu: Reduce synchronize

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Zd4KizFuP4aGuNLE@localhost.localdomain>
Date: Tue, 27 Feb 2024 17:15:07 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: "Paul E . McKenney" <paulmck@...nel.org>, RCU <rcu@...r.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Boqun Feng <boqun.feng@...il.com>, Hillf Danton <hdanton@...a.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v5 2/4] rcu: Reduce synchronize_rcu() latency

Le Tue, Feb 20, 2024 at 07:31:13PM +0100, Uladzislau Rezki (Sony) a écrit :
> +static struct llist_node *rcu_sr_get_wait_head(void)
> +{
> +	struct sr_wait_node *sr_wn;
> +	int i;
> +
> +	for (i = 0; i < SR_NORMAL_GP_WAIT_HEAD_MAX; i++) {
> +		sr_wn = &(rcu_state.srs_wait_nodes)[i];
> +
> +		if (!atomic_cmpxchg_acquire(&sr_wn->inuse, 0, 1))
> +			return &sr_wn->node;
> +	}
> +
> +	return NULL;
> +}
> +
> +static void rcu_sr_put_wait_head(struct llist_node *node)
> +{
> +	struct sr_wait_node *sr_wn = container_of(node, struct sr_wait_node, node);
> +	atomic_set_release(&sr_wn->inuse, 0);

Can we comment this release/acquire pair?

IIUC, the point is that we must make sure that the wait_head->next fetch
happens before it gets reused and rewritten to something else.

Thanks.