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

[Kevin Winchester]

Ingo Molnar wrote:
> * Sitsofe Wheeler <sitsofe@xxxxxxxxx> wrote:
>
> > OK I've managed to bisect this down to commit 
> > [c6531cce6e6e4b99bcda46b6268d6f2d9e30aea4] (sched: do not trace 
> > sched_clock):
> >
> > commit c6531cce6e6e4b99bcda46b6268d6f2d9e30aea4
> > Author: Ingo Molnar <mingo@xxxxxxx>
> > 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@xxxxxxx>
> >     Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >
> > 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@xxxxxxx>
> 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@xxxxxxx>
> > 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@xxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
> ---
>  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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