Re: [PATCH] mm: reject MAP_SHARED_VALIDATE without new flags

[Eric Sandeen <sandeen@sandeen.net>]

On 6/27/18 9:10 PM, Linus Torvalds wrote:
> On Wed, Jun 27, 2018 at 6:45 PM Eric Sandeen <sandeen@redhat.com> wrote:
>>
>> Thus the invalid flag combination of (MAP_SHARED|MAP_PRIVATE) now
>> passes without error, which is a regression.
> 
> It's not a regression, it's just new behavior.
> 
> "regression" doesn't mean "things changed". It means "something broke".
> 
> What broke?

My commit log perhaps was not clear enough.

What broke is that mmap(MAP_SHARED|MAP_PRIVATE) now succeeds without error,
whereas before it rightly returned -EINVAL.

What behavior should a user expect from a successful mmap(MAP_SHARED|MAP_PRIVATE)?

-Eric

> Because if it's some manual page breakage, just fix the manual. That's
> what "new behavior" is all about.
> 
> There is nothing that says that "MAP_SHARED_VALIDATE" can't work with
> just the legacy flags.
> 
> Because I'd be worried about your patch breaking some actual new user
> of MAP_SHARED_VALIDATE.
> 
> Because it's actual *users* of behavior we care about, not some
> test-suite or manual pages.
> 
>               Linus