linux-kernel - Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM

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Message-ID: <4982324B.3050706@oracle.com>
Date:	Thu, 29 Jan 2009 14:48:43 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Maksim Yevmenkin <maksim.yevmenkin@...il.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>, will@...wder-design.com,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED
 	file segments

Maksim Yevmenkin wrote:
> On Thu, Jan 29, 2009 at 12:48 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>> On Thu, 29 Jan 2009, Linus Torvalds wrote:
>>> THIS PATCH IS TOTALLY UNTESTED!
>> Well, it boots. FWIW. I've not really tested anything interesting with it,
>> but any potential breakage is at least not catastrophic and immediate.
>>
>>> diff --git a/mm/mmap.c b/mm/mmap.c
>>> index 8d95902..3f78ead 100644
>>> --- a/mm/mmap.c
>>> +++ b/mm/mmap.c
>>> @@ -769,6 +769,10 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
>>>       if (vm_flags & VM_SPECIAL)
>>>               return NULL;
>>>
>>> +     /* Anonymous shared mappings are unsharable */
>>> +     if ((vm_flags & VM_SHARED) && !file)
>>> +             return NULL;
>>> +
>> .. and I think this part of it is actually unnecessary, because what
>> happens is that a shared anon mapping is turned into a shmem mapping when
>> it is inserted, and that actually ends up allocating a file for it. So the
>> vma->vm_file for anon mappings will not match a NULL file pointer
>> _anyway_, so there's no way it would end up merging.
>>
>> So my patch can be further simplified, I think, to just the following.
>> Even more total lines removed.
>>
>> I still want somebody else to look at and think about it, though.
> 
> Just to confirm. This patch also appear to fix the immediate issue for us.

Is there a (small) test program available?

Thanks,
-- 
~Randy
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