linux-kernel - Re: Linux 2.6.24-rc5 x86 architecture no longer Oopses...

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Date:	Fri, 21 Dec 2007 01:44:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	trond.myklebust@....uio.no, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: Linux 2.6.24-rc5 x86 architecture no longer Oopses...


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> > +		raw_local_irq_save(flags);
> >  		__raw_spin_lock(&die.lock);
> > -		raw_local_save_flags(flags);
> >  		die.lock_owner = smp_processor_id();
> >  		die.lock_owner_depth = 0;
> >  		bust_spinlocks(1);
> > -	}
> > -	else
> > -		raw_local_save_flags(flags);
> > +	} else
> > +		raw_local_irq_save(flags);
> >  
> >  	if (++die.lock_owner_depth < 3) {
> >  		unsigned long esp;
> 
> Looks sane.
> 
> I suppose there's some reason why we can't just use 
> spin_lock_irqsave(). But that reason was either so obvious or so 
> unimportant that a comment was not needed.  Sigh.

bug was introduced via:

  commit 39743c9ef717fd4f2b5583f010115c5f2482b8ae
  Author: Andi Kleen <ak@...e.de>
  Date:   Fri Oct 19 20:35:03 2007 +0200

      x86: use raw locks during oopses

-               spin_lock_irqsave(&die.lock, flags);
+               __raw_spin_lock(&die.lock);
+               raw_local_save_flags(flags);

that is not a correct open-coding of spin_lock_irqsave(): both the 
ordering is wrong (irqs should be disabled _first_), and the wrong 
flags-saving API was used.

so this is a post-2.6.23 regression and the fix is (now) obvious.

	Ingo
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