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

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Date:	Mon, 06 Jun 2011 19:57:45 +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 06.06.2011 19:11, Ingo Molnar wrote:
>
> * Peter Zijlstra<peterz@...radead.org>  wrote:

>
>> +void printk_tick(void)
>> +{
>> +	if (!__this_cpu_read(printk_pending))
>> +		return;
>> +
>> +	/*
>> +	 * Try to acquire and then immediately release the
>> +	 * console semaphore. The release will do all the
>> +	 * actual magic (print out buffers, wake up klogd,
>> +	 * etc).
>> +	 */
>> +	if (console_trylock_for_printk(smp_processor_id())) {
>> +		console_unlock();
>> +		__this_cpu_write(printk_pending, 0);
>> +	}
>> +}
>
> Arne does this fix the hang you are seeing?

What do you want me to test? just replace printk_tick with the
above version? If I do that, the machine doesn't even boot up
any more.

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