linux-kernel - Re: [RFC][PATCH] kmap_atomic

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Date:	Thu, 08 Oct 2009 23:58:30 +0100
From:	David Howells <dhowells@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	dhowells@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC][PATCH] kmap_atomic_push

Peter Zijlstra <peterz@...radead.org> wrote:

> I can think of code that does a lot more than that, suppose you have
> both KM_USER[01], get an interrupt that takes KM_IRQ[01], take an NMI
> that takes KM_NMI.

But whilst the interrupt might want to use two slots, it's probably a bug for
it to want to access the mappings set up by whatever called KM_USER[01] - so
it can probably reuse those slots, provided it puts them back again.

Similarly for NMI taking KM_NMI - it probably shouldn't be attempting to
access the mappings set up by the normal mode or the interrupt mode - in which
case, why can't it reuse those slots?

> Maybe we can stack the SOFTIRQ ones in as well ;-)

Ditto.

David
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