On Fri, Nov 01, 2013 at 02:22:25AM -0700, Michel Lespinasse wrote:
> On Fri, Nov 1, 2013 at 1:43 AM, Peter Zijlstra <[email protected]> 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.
Agreed.
> 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 <[email protected]>
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 <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Reviewed-by: KOSAKI Motohiro <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: David Miller <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Russell King <[email protected]>
Cc: Paul Mundt <[email protected]>
Cc: Jeff Dike <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Namhyung Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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.
Thanks.
--yliu
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