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Date: Sun, 20 Mar 2011 19:20:18 -0700 (PDT)
From: Hugh Dickins <hughd@google.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: mmotm threatens ppc preemption again
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Cc: linuxppc-dev@lists.ozlabs.org, Jeremy Fitzhardinge <jeremy@goop.org>,
	Hugh Dickins <hughd@google.com>, Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
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On Mon, 21 Mar 2011, Benjamin Herrenschmidt wrote:
> 
> As long as the races to avoid are between map/unmap vs. access, yes, it
> -should- be fine, and we used to not do demand faulting on kernel space
> (but for how long ?). I'm wondering why we don't just stick a ptl in
> there or is there a good reason why we can't ?

We can - but we usually prefer to avoid unnecessary locking.
An arch function which locks init_mm.page_table_lock on powerpc,
but does nothing on others?

Hugh