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Subject: Re: Sleeping function called from illegal context...
From: Robert Love <rml@tech9.net>
To: John Levon <movement@marcelothewonderpenguin.com>
Cc: linux-kernel@vger.kernel.org, akpm@digeo.com
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On Sat, 2002-09-28 at 13:24, John Levon wrote:

> NMI interrupt handler cannot block so it trylocks against a spinlock
> instead. Buffer processing code needs to block against concurrent NMI
> interrupts so takes the spinlock for them. All actual blocks on the
> spinlock are beneath a down() on another semaphore, so a sleep whilst
> holding the spinlock won't actually cause deadlock.

If all accesses to the spinlock are taken under a semaphore, then the
spinlock is not needed (i.e. the down'ed semaphore provides the same
protection), or am I missing something?

If this is not the case - e.g. there are other accesses to these locks -
then you cannot sleep, no?

I really can think of no case in which it is safe to sleep while holding
a spinlock or otherwise atomic.  If it is, then the atomicity is not
needed, sort of by definition.

	Robert Love

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