On 08/11/2017 09:59 AM, Rik van Riel wrote:
> On Fri, 2017-08-11 at 09:36 -0700, Mike Kravetz wrote:
>> On 08/11/2017 08:23 AM, Rik van Riel wrote:
>>> On Thu, 2017-08-10 at 17:23 +0200, Michal Hocko wrote:
>>>> On Sun 06-08-17 10:04:25, Rik van Riel wrote:
>>>> [...]
>>>>> diff --git a/kernel/fork.c b/kernel/fork.c
>>>>> index 17921b0390b4..db1fb2802ecc 100644
>>>>> --- a/kernel/fork.c
>>>>> +++ b/kernel/fork.c
>>>>> @@ -659,6 +659,13 @@ static __latent_entropy int
>>>>> dup_mmap(struct
>>>>> mm_struct *mm,
>>>>> tmp->vm_flags &= ~(VM_LOCKED |
>>>>> VM_LOCKONFAULT);
>>>>> tmp->vm_next = tmp->vm_prev = NULL;
>>>>> file = tmp->vm_file;
>>>>> +
>>>>> + /* With VM_WIPEONFORK, the child gets an empty
>>>>> VMA. */
>>>>> + if (tmp->vm_flags & VM_WIPEONFORK) {
>>>>> + tmp->vm_file = file = NULL;
>>>>> + tmp->vm_ops = NULL;
>>>>> + }
>>>>
>>>> What about VM_SHARED/|VM)MAYSHARE flags. Is it OK to keep the
>>>> around?
>>>> At
>>>> least do_anonymous_page SIGBUS on !vm_ops && VM_SHARED. Or do I
>>>> miss
>>>> where those flags are cleared?
>>>
>>> Huh, good spotting. That makes me wonder why the test case that
>>> Mike and I ran worked just fine on a MAP_SHARED|MAP_ANONYMOUS VMA,
>>> and returned zero-filled memory when read by the child process.
>>
>> Well, I think I still got a BUG with a MAP_SHARED|MAP_ANONYMOUS vma
>> on
>> your v2 patch. Did not really want to start a discussion on the
>> implementation until the issue of exactly what VM_WIPEONFORK was
>> supposed
>> to do was settled.
>
> It worked here, but now I don't understand why :)
>
>>>
>>> OK, I'll do a minimal implementation for now, which will return
>>> -EINVAL if MADV_WIPEONFORK is called on a VMA with MAP_SHARED
>>> and/or an mmapped file.
>>>
>>> It will work the way it is supposed to with anonymous MAP_PRIVATE
>>> memory, which is likely the only memory it will be used on, anyway.
>>>
>>
>> Seems reasonable.
>>
>> You should also add VM_HUGETLB to those returning -EINVAL. IIRC, a
>> VM_HUGETLB vma even without VM_SHARED expects vm_file != NULL.
>
> In other words (flags & MAP_SHARED || vma->vm_file) would catch
> hugetlbfs, too?
Yes, that should catch hugetlbfs.
--
Mike Kravetz
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