linux-kernel - Re: [pchecks v2 2/2] percpu: Add preemption checks to __this

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Date:	Fri, 4 Oct 2013 10:27:28 +0200
From:	Peter Zijlstra <peterz@...radead.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, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [pchecks v2 2/2] percpu: Add preemption checks to __this_cpu ops

On Thu, Oct 03, 2013 at 06:28:26PM +0000, Christoph Lameter wrote:
> @@ -538,7 +544,8 @@ do {									\
>  # ifndef __this_cpu_read_8
>  #  define __this_cpu_read_8(pcp)	(*__this_cpu_ptr(&(pcp)))
>  # endif
> -# define __this_cpu_read(pcp)	__pcpu_size_call_return(__this_cpu_read_, (pcp))
> +# define __this_cpu_read(pcp) \
> +	(__this_cpu_preempt_check(),__pcpu_size_call_return(__this_cpu_read_, (pcp)))
>  #endif

Would it not be move convenient to implement it in terms of the
raw_this_cpu*() thingies? That way you're sure they actually do the same
thing and there's only 1 site to change when changing the
implementation.

Something like:

#define __this_cpu_read(pcp) 						\
({									\
	__this_cpu_preempt_check();					\
	raw_this_cpu_read(pcp);						\
})



> @@ -39,8 +39,8 @@ notrace unsigned int debug_smp_processor
>  	if (!printk_ratelimit())
>  		goto out_enable;
>  
> -	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] "
> -			"code: %s/%d\n",
> +	printk(KERN_ERR "%s in preemptible [%08x] "
> +			"code: %s/%d\n", what,
>  			preempt_count() - 1, current->comm, current->pid);

I would argue for keeping the "BUG" string intact and in front of the
%s.

>  	print_symbol("caller is %s\n", (long)__builtin_return_address(0));
>  	dump_stack();
> @@ -51,5 +51,17 @@ out:
>  	return this_cpu;
>  }
>  
> +notrace unsigned int debug_smp_processor_id(void)
> +{
> +	return check_preemption_disabled("BUG: using smp_processor_id()");
> +}
>  EXPORT_SYMBOL(debug_smp_processor_id);
>  
> +notrace void __this_cpu_preempt_check(void)
> +{
> +#ifdef CONFIG_DEBUG_THIS_CPU_OPERATIONS
> +	check_preemption_disabled("__this_cpu operation");
> +#endif

Because here you've forgotten it..

> +}
> +EXPORT_SYMBOL(__this_cpu_preempt_check);
--
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