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Subject: Re: spinlock assertion macros
From: Robert Love <rml@tech9.net>
To: Dave Jones <davej@suse.de>
Cc: Daniel Phillips <phillips@arcor.de>, Jesse Barnes <jbarnes@sgi.com>,
       kernel-janitor-discuss 
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On Fri, 2002-07-12 at 05:07, Dave Jones wrote:

> When I came up with the idea[1] I envisioned some linked-lists frobbing,
> but in more recent times, we can now check the preempt_count for a
> quick-n-dirty implementation (without the additional info of which locks
> we hold, lock-taker, etc).

Neat idea.  I have seen some other good similar ideas: check
preempt_count on schedule(), check preempt_count in usleep/msleep
(Arjan's idea), and check preempt_count in wakeup/context switch/etc.
code...

Note some of these need one or both of: subtracting out
current->lock_depth+1 since we can sleep with the BKL and NAND'ing out
PREEMPT_ACTIVE as that is set before entering schedule off a preemption.

As we move preempt_count to more of a generic "are we atomic" count in
2.5, these become easier and more useful...

	Robert Love

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