linux-kernel - Re: [pchecks v1 4/4] percpu: Add preemption checks to __this

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Date:	Tue, 24 Sep 2013 10:03:47 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
	Steven Rostedt <srostedt@...hat.com>,
	linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [pchecks v1 4/4] percpu: Add preemption checks to __this_cpu ops


* Christoph Lameter <cl@...ux.com> wrote:

> --- linux.orig/kernel/sched/core.c	2013-09-23 10:24:47.371629684 -0500
> +++ linux/kernel/sched/core.c	2013-09-23 10:24:47.371629684 -0500
> @@ -2566,6 +2566,29 @@ asmlinkage void __sched preempt_schedule
>  	exception_exit(prev_state);
>  }
>  
> +#ifdef CONFIG_DEBUG_PREEMPT
> +/*
> + * This function is called if the kernel is compiled with preempt
> + * support for each __this_cpu operations. It verifies that
> + * preemption has been disabled.
> + *
> + * The function cannot be a macro due to the low level nature
> + * of the per cpu header files.
> + */
> +void __this_cpu_preempt_check(void)
> +{
> +	int p;
> +
> +	p = preemptible();
> +	if (p) {
> +		printk(KERN_ERR "__this_cpu but preemptable."
> +			" preempt_count=%d irqs_disabled=%d\n",
> +			preempt_count(), irqs_disabled());
> +		dump_stack();
> +	}
> +
> +}
> +#endif /* CONFIG_DEBUG_PREEMPT */

During past review of your series Peter Zijlstra very explicitly told you 
to reuse (and unify with) the preempt checks in lib/smp_processor_id.c! 
See debug_smp_processor_id().

The problem isn't just that you are duplicating code and adding 
unnecessary #ifdefs into the wrong place, the bigger problem is that you 
are implementing weak checks which creates unnecessary raw_*() pollution 
all across the kernel.

Your lack of cooperation is getting ridiculous!

My NAK still stands, obviously.

Thanks,

	Ingo
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