Re: [PATCH] Fix OOPS in mmap_region() when merging adjacent VM_LOCKED file segments

Randy Dunlap
2009-01-29T22:50:01Z

Maksim Yevmenkin wrote:
> On Thu, Jan 29, 2009 at 12:48 PM, Linus Torvalds
> <torvalds@linux-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