linux-kernel - Re: [BUG] 2.6.27-rc5 couldn't boot on tulsa machine randomly

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Date:	Wed, 10 Sep 2008 17:12:58 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] 2.6.27-rc5 couldn't boot on tulsa machine randomly


On Tue, 2008-09-09 at 11:26 +0800, Zhang, Yanmin wrote:
> On my tulsa x86-64 machine, kernel 2.6.25-rc5 couldn't boot randomly.
> 
> Basically, function __enable_runtime forgets to reset  rt_rq->rt_throttled to 0.
Peter,

Is there any issue with the patch?

I tested 2.6.27-rc6 and it still couldn't boot on my tulsa machine. With my patch,
kernel could boot.

Yanmin


> When every cpu is up, per-cpu migration_thread is created and it runs very fast,
> sometimes to mark the corresponding rt_rq->rt_throttled to 1 very quickly. After
> all cpus are up, with below calling chain,
> sched_init_smp => arch_init_sched_domains => build_sched_domains => ...
> => cpu_attach_domain => rq_attach_root => set_rq_online => ... => __enable_runtime,
> __enable_runtime is called against every rt_rq again, so rt_rq->rt_time is reset to
> 0, but rt_rq->rt_throttled might be still 1. Later on function do_sched_rt_period_timer
> couldn't reset it, and all RT tasks couldn't be scheduled to run on that cpu.
> here is RT task migration_thread which is woken up when a task is migrated to another cpu.
> 
> Below patch fixes it against 2.6.27-rc5.
> 
> Signed-off-by: Zhang Yanmin <yanmin_zhang@...ux.intel.com>
> 
> ---
> 
> diff -Nraup linux-2.6.27-rc5/kernel/sched_rt.c linux-2.6.27-rc5_fix/kernel/sched_rt.c
> --- linux-2.6.27-rc5/kernel/sched_rt.c	2008-09-09 11:06:43.000000000 +0800
> +++ linux-2.6.27-rc5_fix/kernel/sched_rt.c	2008-09-09 11:13:04.000000000 +0800
> @@ -350,6 +350,7 @@ static void __enable_runtime(struct rq *
>  		spin_lock(&rt_rq->rt_runtime_lock);
>  		rt_rq->rt_runtime = rt_b->rt_runtime;
>  		rt_rq->rt_time = 0;
> +		rt_rq->rt_throttled = 0;
>  		spin_unlock(&rt_rq->rt_runtime_lock);
>  		spin_unlock(&rt_b->rt_runtime_lock);
>  	}
> 
> 
> --
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