linux-kernel - Re: [PATCH] Define a UNIQUE value for AS

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Date:	Fri, 3 Apr 2009 03:02:41 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	stable <stable@...nel.org>, Rik van Riel <riel@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH] Define a UNIQUE value for AS_UNEVICTABLE flag

(cc to Avi)

>> [PATCH] Define UNIQUE value of AS_UNEVICTABLE
>>
>> Needed in 2.6.28, 2.6.29, ...
>>
>> A new "address_space flag"--AS_MM_ALL_LOCKS--was defined to use the next
>> available AS flag while the Unevictable LRU was under development.  The
>> Unevictable LRU was using the same flag and "no one" noticed.  Current
>> mainline, since 2.6.28, has same value for two symbolic flag names.
>
> argh.
>
> What are the user-observable effects of the bug, and why didn't anyone
> notice it until now?

AS_MM_ALL_LOCKS is used by mmu_notifier. it mean it is used by only kvm.
In the other hand,  AS_UNEVICTABLE mean unevictable shmem or ramfs.

Then, if shmem opend process use ioctl(KVM_CREATE_VM), unevictable
flag on the shmem accidentally turn off.
but, fortunatelly, In modern desktop environment, only KVM control
program use above ioctl. then, we can assume this doesn't use shmem
and ramfs.

Am I missing anything?
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