linux-kernel - Re: [patch 1/3] mmu

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Message-ID: <Pine.LNX.4.64.0801311852140.6272@schroedinger.engr.sgi.com>
Date:	Thu, 31 Jan 2008 19:01:44 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Robin Holt <holt@....com>
cc:	Andrea Arcangeli <andrea@...ranet.com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 1/3] mmu_notifier: Core code

On Thu, 31 Jan 2008, Robin Holt wrote:

> Both xpmem and GRU have means of removing their context seperate from
> process termination.  XPMEMs is by closing the fd, I believe GRU is
> the same.  In the case of XPMEM, we are able to acquire the mmap_sem.
> For GRU, I don't think it is possible, but I do not remember the exact
> reason.

For any action initiated from user space you will not hold mmap sem. So 
you can call the unregister function. Then you need to do a 
synchronize_rcu before freeing the structures.

It is also possible to shut this down outside via f.e. a control thread. 
The control thread can acquire mmap_sem and then unregister the notifier.

Am I missing something?

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