linux-kernel - Re: Wanted: simple, safe x86 stack overflow detection

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Date:	Wed, 07 Mar 2007 04:34:52 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Bill Irwin <bill.irwin@...cle.com>
Cc:	Hugh Dickins <hugh@...itas.com>, Chuck Ebbert <cebbert@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Wanted: simple, safe x86 stack overflow detection

On Tue, 2007-03-06 at 22:44 -0800, Bill Irwin wrote:
> At some point in the past, I wrote:
> >> I'm certainly in favor of the move; IRQ stacks could be made
> >> rather deep and cheaply at that. I may get around to writing it this
> >> week if no one else does it first.
> 
> On Tue, Mar 06, 2007 at 08:28:35PM -0800, Arjan van de Ven wrote:
> > the irq stacks aren't the problem; RH at some point accidentally shipped
> > a kernel with 4k *shared* irq/user context stack and even that gave
> > almost no issues.
> > irq's really shouldn't actually nest; it's bad for just about everything
> > to do that (but that's another story, I would *love* to get rid of the
> > "enable irqs" thing in the x86 irq path, it hurts just about anything in
> > reality)
> 
> What do you see as the obstacle to eliminating nested IRQ's?

political will, or maybe just the lack of convincing people so far

>  It doesn't
> seem so far out to test for being on the interrupt stack and defer the
> call to do_IRQ() until after the currently-running instance of do_IRQ()
> has returned, or to move to per-irq stacks modulo special arrangements
> for the per-cpu IRQ's. Or did you have other methods in mind?

it's simpler...

irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
{ 
        irqreturn_t ret, retval = IRQ_NONE;
        unsigned int status = 0;

        handle_dynamic_tick(action);
   
        if (!(action->flags & IRQF_DISABLED))
                local_irq_enable_in_hardirq();


just removing the if() and the explicit IRQ enabling already makes irqs no longer nest...

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

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