linux-kernel - [PATCH -mm] only drop root anon

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Date:	Wed, 9 Jun 2010 21:16:17 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org
Subject: [PATCH -mm] only drop root anon_vma if not self

On Wed, 9 Jun 2010 17:19:02 +0800
Dave Young <hidave.darkstar@...il.com> wrote:

> > Manually bisected mm patches, the memleak caused by following patch:
> >
> > mm-extend-ksm-refcounts-to-the-anon_vma-root.patch
>
> 
> So I guess the refcount break, either drop-without-get or over-drop

I'm guessing I did not run the kernel with enough debug options enabled
when I tested my patches...

Dave & Catalin, thank you for tracking this down.

Dave, does the below patch fix your issue?

Andrew, if the patch below works, you'll probably want to merge it as
mm-extend-ksm-refcounts-to-the-anon_vma-root-fix.patch :)

----------------

With the new anon_vma code we take a refcount on the root anon_vma.
However, the root anon_vma does not have a refcount on itself, so
we should not try to do a drop on itself when it is being unlinked.

Signed-off-by: Rik van Riel <riel@...hat.com>

--- linux-2.6-rtavma/mm/rmap.c.orig	2010-06-09 21:10:07.349376896 -0400
+++ linux-2.6-rtavma/mm/rmap.c	2010-06-09 21:10:24.180406299 -0400
@@ -275,7 +275,8 @@ static void anon_vma_unlink(struct anon_
 
 	if (empty) {
 		/* We no longer need the root anon_vma */
-		drop_anon_vma(anon_vma->root);
+		if (anon_vma->root != anon_vma)
+			drop_anon_vma(anon_vma->root);
 		anon_vma_free(anon_vma);
 	}
 }
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