Messages in this thread |  | | Date | Fri, 1 Nov 2013 18:07:07 +0800 | From | Yuanhan Liu <> | Subject | Re: [PATCH 1/4] mm/rmap: per anon_vma lock |
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On Fri, Nov 01, 2013 at 02:22:25AM -0700, Michel Lespinasse wrote: > On Fri, Nov 1, 2013 at 1:43 AM, Peter Zijlstra <peterz@infradead.org> 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 <a.p.zijlstra@chello.nl> 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 <a.p.zijlstra@chello.nl> Acked-by: Hugh Dickins <hughd@google.com> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: David Miller <davem@davemloft.net> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Paul Mundt <lethal@linux-sh.org> Cc: Jeff Dike <jdike@addtoit.com> Cc: Richard Weinberger <richard@nod.at> Cc: Tony Luck <tony.luck@intel.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Mel Gorman <mel@csn.ul.ie> Cc: Nick Piggin <npiggin@kernel.dk> Cc: Namhyung Kim <namhyung@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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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