linux-kernel - Re: [PATCH 05/48] percpu: Add preemption checks to __this

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Date:	Tue, 4 Mar 2014 18:27:18 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux.com>, Tejun Heo <tj@...nel.org>,
	akpm@...uxfoundation.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 05/48] percpu: Add preemption checks to __this_cpu ops

On Tue, 4 Mar 2014 14:27:27 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Fri, 14 Feb 2014 14:18:46 -0600 Christoph Lameter <cl@...ux.com> wrote:
> 
> > [Patch depends on another patch in this series that introduces raw_cpu_ops]
> > 
> > We define a check function in order to avoid trouble with the
> > include files. Then the higher level __this_cpu macros are
> > modified to invoke the preemption check.
> > 
> > --- linux.orig/lib/smp_processor_id.c	2014-01-30 14:40:50.936519233 -0600
> > +++ linux/lib/smp_processor_id.c	2014-01-30 14:40:50.936519233 -0600
> > @@ -7,7 +7,7 @@
> >  #include <linux/kallsyms.h>
> >  #include <linux/sched.h>
> >  
> > -notrace unsigned int debug_smp_processor_id(void)
> > +notrace static unsigned int check_preemption_disabled(char *what)
> >  {
> >  	int this_cpu = raw_smp_processor_id();
> >  
> > @@ -38,9 +38,9 @@
> >  	if (!printk_ratelimit())
> >  		goto out_enable;
> >  
> > -	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] "
> > -			"code: %s/%d\n",
> > -			preempt_count() - 1, current->comm, current->pid);
> > +	printk(KERN_ERR "BUG: using %s in preemptible [%08x] code: %s/%d\n",
> > +		what, preempt_count() - 1, current->comm, current->pid);
> > +
> >  	print_symbol("caller is %s\n", (long)__builtin_return_address(0));
> >  	dump_stack();
> 
> I wonder if there's any point in printing __builtin_return_address. 
> Doesn't dump_stack() tell us the same thing?

When frame pointers are enabled, sure. But without frame pointers, I'm
not so sure.

-- Steve
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