linux-kernel - Re: [patch] x86, pat: freeing invalid memtype messages

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Message-ID: <4C2023D0.7010309@redhat.com>
Date:	Tue, 22 Jun 2010 10:45:36 +0800
From:	Xiaotian Feng <dfeng@...hat.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	Dan Carpenter <error27@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, "H.PeterA" <nvinhpa@...or.com>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Jack Steiner <steiner@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [patch] x86, pat: freeing invalid memtype messages

On 06/22/2010 01:54 AM, Suresh Siddha wrote:
> On Mon, 2010-06-21 at 08:41 -0700, Peter Zijlstra wrote:
>> On Mon, 2010-06-21 at 17:33 +0200, Marcin Slusarz wrote:
>>> On Mon, Jun 21, 2010 at 07:07:27PM +0800, Xiaotian Feng wrote:
>>>> On 06/21/2010 07:02 PM, Peter Zijlstra wrote:
>>>>> On Mon, 2010-06-21 at 18:56 +0800, Xiaotian Feng wrote:
>>>>>
>>>>>> I guess there might be something wrong between the augmented rbtree insert/remove ..
>>>>>
>>>>> The easiest thing is to revert that change and try again, the next step
>>>>> would be to print the full RB tree on each modification and look where
>>>>> it goes wrong.
>>>>>
>>>>> That said, I did print my fair share of (augmented) RB trees while
>>>>> playing with scheduler patches and I can't remember it ever having
>>>>> messed up like that.
>>>> He's using 2.6.35-rc2+, without your "rbtree: Undo augmented trees
>>>> performance damage" patch ;-)
>>>
>>> I applied it manually (commit 2463eb8b3093995e09a0d41b3d78ee0cf5fb4249 from -tip)
>>> to 2.6.35-rc3 and it fixed both acpi's and nouveau's "invalid memtype" messages.
>>> Thanks.
>>
>> Oh neat, so it actually fixes a bug in the previous augmented rb-tree
>> implementation?
>
> When I was reviewing your fix, it looked like that prior to your fix we
> were re-augmenting only at points where we do the tree rotations/color
> change and at the points of node insertion/removal. I don't think we
> were re-augmenting all the parent nodes in the path of the selected-node
> that is going to replace the deleted node.
>
> Perhaps we were hitting this issue here.

Were it from a insert without any rotations/color changes?

This case is performing insert A/remove A/ 2nd insert A/ 2nd remove 
A/3rd insert A. And the 2nd remove
shows us the invalid memtype.  3rd insert shows us it is in the rbtree. 
All I can image is that get_subtree_max_end
in memtype_rb_lowest_match returned stale value.

It looks like we don't re-augment the parent nodes if there aren't any 
rotations/color changes
in the rb_insert_color().

>
> thanks,
> suresh
>
>

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