Re: [PATCH v2 0/2] mm,fork,security: introduce MADV_WIPEONFORK

[Florian Weimer <fweimer@redhat.com>]

On 08/08/2017 05:19 PM, Mike Kravetz wrote:
> On 08/08/2017 06:15 AM, Rik van Riel wrote:
>> On Tue, 2017-08-08 at 11:58 +0200, Florian Weimer wrote:
>>> On 08/07/2017 08:23 PM, Mike Kravetz wrote:
>>>> If my thoughts above are correct, what about returning EINVAL if
>>>> one
>>>> attempts to set MADV_DONTFORK on mappings set up for sharing?
>>>
>>> That's my preference as well.  If there is a use case for shared or
>>> non-anonymous mappings, then we can implement MADV_DONTFORK with the
>>> semantics for this use case.  If we pick some arbitrary semantics
>>> now,
>>> without any use case, we might end up with something that's not
>>> actually
>>> useful.
>>
>> MADV_DONTFORK is existing semantics, and it is enforced
>> on shared, non-anonymous mappings. It is frequently used
>> for things like device mappings, which should not be
>> inherited by a child process, because the device can only
>> be used by one process at a time.
>>
>> When someone requests MADV_DONTFORK on a shared VMA, they
>> will get it. The later madvise request overrides the mmap
>> flags that were used earlier.
>>
>> The question is, should MADV_WIPEONFORK (introduced by
>> this series) have not just different semantics, but also
>> totally different behavior from MADV_DONTFORK?
> 
> Sorry for the confusion.  I accidentally used MADV_DONTFORK instead
> of MADV_WIPEONFORK in my reply (which Florian commented on).

Yes, I made the same mistake.  I meant MADV_WIPEONFORK as well.

Florian