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Subject: Re: [PATCH] update fix X86_64 procfs provide stack information for
 threads
From: Stefani Seibold <stefani@seibold.net>
To: Andi Kleen <andi@firstfloor.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Americo Wang <xiyou.wangcong@gmail.com>
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Date: Wed, 04 Nov 2009 16:42:11 +0100
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Am Mittwoch, den 04.11.2009, 13:00 +0100 schrieb Andi Kleen:
> > This is true, but i think it is better to get an outdated value than a
> > complete wrong value like -1.
> 
> -1 means "I don't know".  I don't think "completely wrong" 
> is the correct term to describe that.
> 
> > The truth is that KSTK_ESP always return an outdated value on a multi
> > core system if the process never do a system call.
> 
> I think not supporting updates on interrupts at least is very poor.
> Unfortunately there's no good way fast path way to detect this I know of
> (that is why I originally added -1 here)

This is a first draft for supporting interrupts:

unsigned int __irq_entry do_IRQ(struct pt_regs *regs)
{
	struct pt_regs *old_regs = set_irq_regs(regs);

	/* high bit used in ret_from_ code  */
	unsigned vector = ~regs->orig_ax;
	unsigned irq;

	exit_idle();
	irq_enter();

/* >>>>>>>> update usersp */  
	current->thread.usersp = regs->sp;

	irq = __get_cpu_var(vector_irq)[vector];

	if (!handle_irq(irq, regs)) {
		ack_APIC_irq();

		if (printk_ratelimit())
			pr_emerg("%s: %d.%d No irq handler for vector (irq %d)\n",
				__func__, smp_processor_id(), vector, irq);
	}

	irq_exit();

	set_irq_regs(old_regs);
	return 1;
}

This works in my environment, but i have not the oversight if it work
under all circumstances. And we need a similar line in the timer
interrupt.

Greetings,
Stefani