linux-kernel - Re: [ckrm-tech] [RFC][PATCH 2/6] task's cpu information needs to be always correct

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Date:	Tue, 12 Jun 2007 07:47:08 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	vatsa@...ux.vnet.ibm.com
CC:	Ingo Molnar <mingo@...e.hu>, Nick Piggin <nickpiggin@...oo.com.au>,
	wli@...omorphy.com, ckrm-tech@...ts.sourceforge.net,
	balbir@...ibm.com, efault@....de, pwil3058@...pond.net.au,
	kernel@...ivas.org, linux-kernel@...r.kernel.org,
	dmitry.adamushko@...il.com, tingy@...umass.edu,
	tong.n.li@...el.com, containers@...ts.osdl.org,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org
Subject: Re: [ckrm-tech] [RFC][PATCH 2/6] task's cpu information needs to
 be always correct

Srivatsa Vaddagiri wrote:
> We rely very much on task_cpu(p) to be correct at all times, so that we
> can correctly find the runqueue from which the task has to be removed or
> added to.
> 
> There is however one place in the scheduler where this assumption of
> task_cpu(p) being correct is broken. This patch fixes that piece of
> code.
> 
> (Thanks to Balbir Singh for pointing this out to me)
> 
> Signed-off-by : Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
> 

Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com>

> ---
>  kernel/sched.c |    8 +++++---
>  1 files changed, 5 insertions(+), 3 deletions(-)
> 
> Index: current/kernel/sched.c
> ===================================================================
> --- current.orig/kernel/sched.c	2007-06-09 15:07:17.000000000 +0530
> +++ current/kernel/sched.c	2007-06-09 15:07:32.000000000 +0530
> @@ -4624,7 +4624,7 @@
>  static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
>  {
>  	struct rq *rq_dest, *rq_src;
> -	int ret = 0;
> +	int ret = 0, on_rq;
> 
>  	if (unlikely(cpu_is_offline(dest_cpu)))
>  		return ret;
> @@ -4640,9 +4640,11 @@
>  	if (!cpu_isset(dest_cpu, p->cpus_allowed))
>  		goto out;
> 
> -	set_task_cpu(p, dest_cpu);
> -	if (p->se.on_rq) {
> +	on_rq = p->se.on_rq;
> +	if (on_rq)
>  		deactivate_task(rq_src, p, 0);
> +	set_task_cpu(p, dest_cpu);
> +	if (on_rq) {
>  		activate_task(rq_dest, p, 0);
>  		check_preempt_curr(rq_dest, p);
>  	}


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
-
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