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Date: Thu, 17 Apr 2008 12:10:52 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: Andrea Arcangeli <andrea@qumranet.com>
cc: Robin Holt <holt@sgi.com>, akpm@linux-foundation.org,
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Subject: Re: [PATCH 1 of 9] Lock the entire mm to prevent any mmu related
 operation to happen
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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?