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

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Message-ID: <20110605151323.GA30590@elte.hu>
Date:	Sun, 5 Jun 2011 17:13:23 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arne Jansen <lists@...-jansens.de>
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


* 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?

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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