linux-kernel - Re: [PATCH][GIT PULL] trace,x86: Move creation of irq tracepoints from apic.c to irq.c

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Message-ID: <1371926797.18733.155.camel@gandalf.local.home>
Date:	Sat, 22 Jun 2013 14:46:37 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH][GIT PULL] trace,x86: Move creation of irq tracepoints
 from apic.c to irq.c

On Sat, 2013-06-22 at 17:42 +0000, Seiji Aguchi wrote:
> > +static inline void load_current_idt(void)
> > +{
> > +       unsigned long flags;
> > +
> > +       local_irq_save(flags);
> > +       if (is_debug_idt_enabled())
> > +               load_debug_idt();
> > +       else
> > +               load_idt((const struct desc_ptr *)&idt_descr);
> > +       local_irq_restore(flags);
> > +}
> > 
> > It's not safe to call local_irq_save() here. From entry_64.S:
> > 
> > .macro TRACE_IRQS_OFF_DEBUG
> > 	call debug_stack_set_zero
> > 	TRACE_IRQS_OFF
> > 	call debug_stack_reset
> > .endm
> > 
> > We must change the idt before we can trace irqs being disabled. The
> > local_irq_save() here is going to be traced by lockdep. Why do we need
> > to disable interrupts? It's pretty pointless since this same code can be
> > called by NMIs.
> 
> OK, I agree to remove the local_irq_save().
> 
> I thought it is safe to disable interrupt to avoid potential races, 
> because the load_current_id() is a common function and someone else may use it near future.

It should not be that common of a function. Not many should use it.

I'm testing a patch now and should post it in a few hours.

-- Steve


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