linux-kernel - Re: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages

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Date:	Sun, 05 Jun 2011 17:34:46 +0200
From:	Arne Jansen <lists@...-jansens.de>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	efault@....de, npiggin@...nel.dk, akpm@...ux-foundation.org,
	frank.rowand@...sony.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI
 watchdog messages

On 05.06.2011 17:13, Ingo Molnar wrote:
>
> * Arne Jansen<lists@...-jansens.de>  wrote:
>
>> sched.c:934: in function __task_rq_lock
>>          lockdep_assert_held(&p->pi_lock);
>
> Oh. Could you remove that line with the patch below - does it result
> in a working system?

yes.

>
> Now, this patch alone just removes a debugging check - but i'm not
> sure the debugging check is correct - we take the pi_lock in a raw
> way - which means it's not lockdep covered.
>
> So how can lockdep_assert_held() be called on it?
>
> Thanks,
>
> 	Ingo
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index fd18f39..a32316b 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -938,8 +938,6 @@ static inline struct rq *__task_rq_lock(struct task_struct *p)
>   {
>   	struct rq *rq;
>
> -	lockdep_assert_held(&p->pi_lock);
> -
>   	for (;;) {
>   		rq = task_rq(p);
>   		raw_spin_lock(&rq->lock);
> --
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