linux-ext4 - Re: [PATCH] mm: reject MAP_SHARED

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Date:   Wed, 27 Jun 2018 21:17:55 -0500
From:   Eric Sandeen <sandeen@...deen.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Eric Sandeen <sandeen@...hat.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux API <linux-api@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-ext4@...r.kernel.org,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>,
        zhibli@...hat.com
Subject: Re: [PATCH] mm: reject MAP_SHARED_VALIDATE without new flags

On 6/27/18 9:10 PM, Linus Torvalds wrote:
> On Wed, Jun 27, 2018 at 6:45 PM Eric Sandeen <sandeen@...hat.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