linux-kernel - Re: [patch] sched: fix set_task_cpu() and provide an unlocked runqueue variant

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: <1259173672.4027.732.camel@laptop>
Date:	Wed, 25 Nov 2009 19:27:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <efault@....de>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch] sched: fix set_task_cpu() and provide an unlocked
 runqueue variant

On Sun, 2009-11-22 at 13:09 +0100, Mike Galbraith wrote:
> sched: fix set_task_cpu() and provide an unlocked runqueue variant.
> 
> set_task_cpu() falsifies migration stats by unconditionally generating migration
> stats whether a task's cpu actually changed or not.  As used in copy_process(),
> the runqueue is unlocked, so we need to provide an unlocked variant which does
> the locking to provide a write barrier.
> 
> Signed-off-by: Mike Galbraith <efault@....de>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> LKML-Reference: <new-submission>
> 
> ---

> +void set_task_cpu_unlocked(struct task_struct *p, unsigned int new_cpu)
> +{
> +	unsigned long flags;
> +	struct rq *rq, *new_rq = cpu_rq(new_cpu);
> +
> +	smp_wmb();
> +	rq = task_rq_lock(p, &flags);
> +	update_rq_clock(rq);
> +	if (rq != new_rq)
> +		update_rq_clock(new_rq);
> +	set_task_cpu(p, new_cpu);
> +	task_rq_unlock(rq, &flags);
> +}

I've got to ask, what's that barrier for?



--
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/