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SubjectRe: [PATCH 1/4] mm/rmap: per anon_vma lock
On Fri, Nov 01, 2013 at 02:22:25AM -0700, Michel Lespinasse wrote:
> On Fri, Nov 1, 2013 at 1:43 AM, Peter Zijlstra <> wrote:
> > AFAICT this isn't correct at all. We used to protect the vma interval
> > tree with the root lock, now we don't. All we've got left is the
> > mmap_sem, but anon_vma chains can cross address-spaces and thus we're up
> > some creek without no paddle.
> Yes, that was my first thought as well (though I wanted to double
> check at first).
> I also want to point out that lately we've seen several changes sent
> out that relax locking with no accompanying explanation of why the
> relaxed locking would be safe. Please don't do that - having a lot of
> performance data is worthless if you can't explain why the new locking
> is safe.


> And I'm not asking to prove a negative ('lack of any possible
> races') there, but at least in this case one could dig out why the
> root anon vma locking was introduced and if they think that this
> reason doesn't apply anymore, explain why...

It was introduced by commit 2b575eb6(And, BTW, I'm sorry that this commit log
about bb4aa39676f is wrong)

commit 2b575eb64f7a9c701fb4bfdb12388ac547f6c2b6
Author: Peter Zijlstra <>
Date: Tue May 24 17:12:11 2011 -0700

mm: convert anon_vma->lock to a mutex

Straightforward conversion of anon_vma->lock to a mutex.

Signed-off-by: Peter Zijlstra <>
Acked-by: Hugh Dickins <>
Reviewed-by: KOSAKI Motohiro <>
Cc: Benjamin Herrenschmidt <>
Cc: David Miller <>
Cc: Martin Schwidefsky <>
Cc: Russell King <>
Cc: Paul Mundt <>
Cc: Jeff Dike <>
Cc: Richard Weinberger <>
Cc: Tony Luck <>
Cc: KAMEZAWA Hiroyuki <>
Cc: Mel Gorman <>
Cc: Nick Piggin <>
Cc: Namhyung Kim <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>

As you can see, Peter didn't tell why before. Honestly speaking, that
was my originaly concern as well. I tried to find some possible races;
I guess I may miss something.



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