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Date: Tue, 04 Dec 2001 13:25:40 -0800
From: george anzinger <george@mvista.com>
Organization: Monta Vista Software
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To: Robert Love <rml@tech9.net>
CC: linux-kernel@vger.kernel.org, Manfred Spraul <manfred@colorfullife.com>
Subject: Re: [PATCH] improve spinlock debugging
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		<3C0D3283.4DA4DD2B@mvista.com> <1007499102.1303.24.camel@phantasy>
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Robert Love wrote:
> 
> On Tue, 2001-12-04 at 15:30, george anzinger wrote:
> 
> > spin_lockirq
> >
> > spin_unlock
> >
> > restore_irq
> 
> Given this order, couldn't we _always_ not touch the preempt count since
> irq's are off?
> 
> Further, since I doubt we ever see:
> 
>         spin_lock_irq
>         restore_irq
>         spin_unlock
> 
> and the common use is:
> 
>         spin_lock_irq
>         spin_unlock_irq
> 
> Isn't it safe to have spin_lock_irq *never* touch the preempt count?
> 
NO.  The problem is the first example above.  The spin_unlock will down
count, but the spin_lockirq did NOT do the paired up count (been there,
done that).  This is where we need the spin_unlock_no_irq_restore.
-- 
George           george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Real time sched: http://sourceforge.net/projects/rtsched/
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