linux-kernel - Re: [PATCH 1 of 9] Lock the entire mm to prevent any mmu related operation to happen

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Message-ID: <Pine.LNX.4.64.0804171202420.23938@schroedinger.engr.sgi.com>
Date:	Thu, 17 Apr 2008 12:10:52 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	Robin Holt <holt@....com>, akpm@...ux-foundation.org,
	Nick Piggin <npiggin@...e.de>,
	Steve Wise <swise@...ngridcomputing.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	Roland Dreier <rdreier@...co.com>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org,
	Avi Kivity <avi@...ranet.com>, kvm-devel@...ts.sourceforge.net,
	general@...ts.openfabrics.org, Hugh Dickins <hugh@...itas.com>
Subject: Re: [PATCH 1 of 9] Lock the entire mm to prevent any mmu related
 operation to happen

On Thu, 17 Apr 2008, Andrea Arcangeli wrote:

> Also note, EMM isn't using the clean hlist_del, it's implementing list
> by hand (with zero runtime gain) so all the debugging may not be
> existent in EMM, so if it's really a mm_lock race, and it only
> triggers with mmu notifiers and not with EMM, it doesn't necessarily
> mean EMM is bug free. If you've a full stack trace it would greatly
> help to verify what is mangling over the list when the oops triggers.

EMM was/is using a single linked list which allows atomic updates. Looked 
cleaner to me since doubly linked list must update two pointers.

I have not seen docs on the locking so not sure why you use rcu 
operations here? Isnt the requirement to have either rmap locks or 
mmap_sem held enough to guarantee the consistency of the doubly linked list?


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