linux-kernel - Re: [X86][BISECTED] WARNING: at kernel/lockdep.c:2680

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Date:	Thu, 05 Jun 2008 20:53:13 -0300
From:	Kevin Winchester <kjwinchester@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Sitsofe Wheeler <sitsofe@...oo.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [X86][BISECTED] WARNING: at kernel/lockdep.c:2680

Ingo Molnar wrote:
> * Sitsofe Wheeler <sitsofe@...oo.com> wrote:
> 
>> OK I've managed to bisect this down to commit 
>> [c6531cce6e6e4b99bcda46b6268d6f2d9e30aea4] (sched: do not trace 
>> sched_clock):
>>
>> commit c6531cce6e6e4b99bcda46b6268d6f2d9e30aea4
>> Author: Ingo Molnar <mingo@...e.hu>
>> Date:   Mon May 12 21:21:14 2008 +0200
>>
>>     sched: do not trace sched_clock
>>
>>     The tracer uses sched_clock, so do not trace it.
>>
>>     Signed-off-by: Ingo Molnar <mingo@...e.hu>
>>     Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>>
>> Reverting this made the lockdep warning go away. Here is the bisection log:
> 
> ah, good find! Does the patch below (instead of the full revert) fix it 
> as well? I've queued the fix up into tip/tracing/ftrace.
> 
> 	Ingo
> 
> ---------------->
> Subject: sched: sched_clock() lockdep fix
> From: Ingo Molnar <mingo@...e.hu>
> Date: Thu Jun 05 15:04:17 CEST 2008
> 
> Sitsofe Wheeler reported a lockdep warning and bisected it down to:
> 
>> commit c6531cce6e6e4b99bcda46b6268d6f2d9e30aea4
>> Author: Ingo Molnar <mingo@...e.hu>
>> Date:   Mon May 12 21:21:14 2008 +0200
>>
>>     sched: do not trace sched_clock
> 
> do not use raw irq flags in cpu_clock() as it causes lockdep to lose
> track of the true state of the IRQ flag.
> 
> Reported-and-bisected-by: Sitsofe Wheeler <sitsofe@...oo.com>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> ---
>  kernel/sched.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Index: linux/kernel/sched.c
> ===================================================================
> --- linux.orig/kernel/sched.c
> +++ linux/kernel/sched.c
> @@ -862,7 +862,7 @@ unsigned long long notrace cpu_clock(int
>  	unsigned long long prev_cpu_time, time, delta_time;
>  	unsigned long flags;
>  
> -	raw_local_irq_save(flags);
> +	local_irq_save(flags);
>  	prev_cpu_time = per_cpu(prev_cpu_time, cpu);
>  	time = __cpu_clock(cpu) + per_cpu(time_offset, cpu);
>  	delta_time = time-prev_cpu_time;
> @@ -871,7 +871,7 @@ unsigned long long notrace cpu_clock(int
>  		time = __sync_cpu_clock(time, cpu);
>  		per_cpu(prev_cpu_time, cpu) = time;
>  	}
> -	raw_local_irq_restore(flags);
> +	local_irq_restore(flags);
>  
>  	return time;
>  }
> 

I didn't manage to get through a bisection run for the warning - thanks 
to Sitsofe for doing it.  The patch does eliminate the warning for me.

Thanks,

-- 
Kevin Winchester

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