linux-kernel - Re: [Patch] Idle balancer: cache align nohz structure to improve idle load balancing scalability

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]

Date:	Wed, 2 Nov 2011 19:24:14 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Venki Pallipadi <venki@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Patch] Idle balancer: cache align nohz structure to improve
 idle load balancing scalability

* Suresh Siddha <suresh.b.siddha@...el.com> [2011-11-01 16:52:38]:

> +	/*
> +	 * We were recently in tickless idle mode. We will do the delayed
> +	 * update of busy mode now (first busy tick after returning from idle).
> +	 */
> +	if (unlikely(rq->tick_stopped)) {
> +		cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
> +
> +		if (cpumask_bits(nohz.idle_cpus_mask)[BIT_WORD(cpu)] == 0 &&
> +		    cpumask_empty(nohz.idle_cpus_mask))
> +			clear_bit(NOHZ_NEED_BALANCING, &nohz.bits);

Can't this clear_bit race with set_bit() in select_nohz_load_balancer()?

   CPU0				CPU1

cpumask_clear_cpu()
if ( ...)
				cpumask_set_cpu();
				set_bit();

	clear_bit();

?

- vatsa

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/