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

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Date:	Thu, 10 Jun 2010 09:30:12 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Rik van Riel <riel@...hat.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: Re: [PATCH -mm] only drop root anon_vma if not self

On Thu, Jun 10, 2010 at 9:16 AM, Rik van Riel <riel@...hat.com> wrote:
> 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?

Yes, it fixed the issue. Thanks.

Tested-by: Dave Young <hidave.darkstar@...il.com>

>
> 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);
>        }
>  }
>



-- 
Regards
dave
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