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Date: Tue, 1 Jun 2010 15:04:02 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Rik van Riel <riel@...hat.com> Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, Mel Gorman <mel@....ul.ie>, Andrea Arcangeli <aarcange@...hat.com>, Minchan Kim <minchan.kim@...il.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Lee Schermerhorn <Lee.Schermerhorn@...com>, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: Re: [PATCH 2/5] change direct call of spin_lock(anon_vma->lock) to inline function On Wed, 26 May 2010 15:39:26 -0400 Rik van Riel <riel@...hat.com> wrote: > @@ -303,10 +303,10 @@ again: > goto out; > > anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); > - spin_lock(&anon_vma->lock); > + anon_vma_lock(anon_vma); > > if (page_rmapping(page) != anon_vma) { > - spin_unlock(&anon_vma->lock); > + anon_vma_unlock(anon_vma); > goto again; > } > This bit is dependent upon Peter's mm-revalidate-anon_vma-in-page_lock_anon_vma.patch (below). I've been twiddling thumbs for weeks awaiting the updated version of that patch (hint). Do we think that this patch series is needed in 2.6.35? If so, why? And if so I guess we'll need to route around mm-revalidate-anon_vma-in-page_lock_anon_vma.patch, or just merge it as-is. From: Peter Zijlstra <a.p.zijlstra@...llo.nl> There is nothing preventing the anon_vma from being detached while we are spinning to acquire the lock. Most (all?) current users end up calling something like vma_address(page, vma) on it, which has a fairly good chance of weeding out wonky vmas. However suppose the anon_vma got freed and re-used while we were waiting to acquire the lock, and the new anon_vma fits with the page->index (because that is the only thing vma_address() uses to determine if the page fits in a particular vma, we could end up traversing faulty anon_vma chains. Close this hole for good by re-validating that page->mapping still holds the very same anon_vma pointer after we acquire the lock, if not be utterly paranoid and retry the whole operation (which will very likely bail, because it's unlikely the page got attached to a different anon_vma in the meantime). Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Hugh Dickins <hugh.dickins@...cali.co.uk> Cc: Linus Torvalds <torvalds@...ux-foundation.org> Reviewed-by: Rik van Riel <riel@...hat.com> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> --- mm/rmap.c | 7 +++++++ 1 file changed, 7 insertions(+) diff -puN mm/rmap.c~mm-revalidate-anon_vma-in-page_lock_anon_vma mm/rmap.c --- a/mm/rmap.c~mm-revalidate-anon_vma-in-page_lock_anon_vma +++ a/mm/rmap.c @@ -370,6 +370,7 @@ struct anon_vma *page_lock_anon_vma(stru unsigned long anon_mapping; rcu_read_lock(); +again: anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping); if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON) goto out; @@ -378,6 +379,12 @@ struct anon_vma *page_lock_anon_vma(stru anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); spin_lock(&anon_vma->lock); + + if (page_rmapping(page) != anon_vma) { + spin_unlock(&anon_vma->lock); + goto again; + } + return anon_vma; out: rcu_read_unlock(); _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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