linux-kernel - Re: [PATCH] procfs: fix /proc/<pid>/maps heap check

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Date:	Thu, 3 Mar 2011 14:22:39 +0200 (EET)
From:	Aaro Koskinen <aaro.koskinen@...ia.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, stable@...nel.org
Subject: Re: [PATCH] procfs: fix /proc/<pid>/maps heap check

Hi,

On Thu, 3 Mar 2011, Aaro Koskinen wrote:
> On Thu, 3 Mar 2011, KOSAKI Motohiro wrote:
>>> On Tue, 1 Mar 2011, Aaro Koskinen wrote:
>>>> The current check looks wrong and prints "[heap]" only if the mapping
>>>> matches exactly the heap. However, the heap may be merged with some
>>>> other mappings, and there may be also be multiple mappings.
>>>> 
>>>> Signed-off-by: Aaro Koskinen <aaro.koskinen@...ia.com>
>>>> Cc: stable@...nel.org
>
> [...]
>
>> Your description said,
>> 	the heap may be merged with some other mappings,
>>                        ^^^^^^
>> but your example is splitting case. not merge. In other words, your
>> patch care splitting case but break merge case.
>> 
>> Ok, we have no obvious correct behavior. This is debatable. So,
>> Why do you think vma splitting case is important than merge?
>
> Sorry, I was unclear.
>
> The current behaviour is wrong for both merged and split cases, and I
> think the patch fixes both.

Argh, this is confusing. The current check:

 	vma->vm_start <= mm->start_brk && vma->vm_end >= mm->brk

obviously works with the merged case. The patch changes this to:

 	vma->vm_start <= mm->brk && vma->vm_end >= mm->start_brk

This works with the split case, but it does not break the merged case
(or do I miss something still?).

So the current behaviour is broken only with the splitting case. I will
correct the patch description and resend it.

A.
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