linux-kernel - Re: [PATCH 1/1] sparc: task_cpu() for stopper thread on sparc32 returns 0

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Date:	Thu, 19 Apr 2012 17:34:28 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Konrad Eisele <konrad@...sler.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>
Cc:	sparclinux@...r.kernel.org, davem@...emloft.net, daniel@...sler.com
Subject: Re: [PATCH 1/1] sparc: task_cpu() for stopper thread on sparc32
	returns 0

Added a few more people - as this patch touches a core file.

I expect we have an issue on sparc32 - that manifest
in this bug. But I do not know this code at all.

	Sam

On Thu, Apr 19, 2012 at 11:22:42AM +0200, Konrad Eisele wrote:
> The stopper thread for CPU > 0 (at least in sparc32)
> has on initialization task_cpu() set to zero even
> for CPUs > 0. The patch explicitly checks weather the
> CPU is allowed to run on the cpu that task_cpu()
> return or changes the return cpu.
> 
> Signed-off-by: Konrad Eisele <konrad@...sler.com>
> ---
>  kernel/sched/stop_task.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
> index 7b386e8..9201866 100644
> --- a/kernel/sched/stop_task.c
> +++ b/kernel/sched/stop_task.c
> @@ -13,7 +13,14 @@
>  static int
>  select_task_rq_stop(struct task_struct *p, int sd_flag, int flags)
>  {
> -	return task_cpu(p); /* stop tasks as never migrate */
> +	int ccpu, cpu , dcpu;
> +	ccpu = cpu = task_cpu(p);
> +	if (unlikely(!cpumask_test_cpu(cpu, tsk_cpus_allowed(p)))) {
> +		cpu = cpumask_first(tsk_cpus_allowed(p));
> +		if (cpu >= nr_cpu_ids)
> +			cpu = ccpu;
> +	}
> +	return cpu;
>  }
>  #endif /* CONFIG_SMP */
>  
> -- 
> 1.6.1.3
> 
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