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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 9 Aug 2021 14:25:17 -0700
Message-ID: <CAHk-=wigKQqEqt9ev_1k5b_DwFGp7JmCdCR1xFSJjOyisEJ61A@mail.gmail.com>
Subject: Re: [GIT PULL] overlayfs fixes for 5.14-rc6
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-unionfs@vger.kernel.org
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On Mon, Aug 9, 2021 at 10:00 AM Miklos Szeredi <miklos@szeredi.hu> wrote:
>
>       ovl: fix mmap denywrite

Ugh. Th edances with denywrite and mapping_unmap_writable are really
really annoying.

I've pulled this, but I really get the feeling that there's duplicated
code for these things, and that all the "if error goto" cases  (some
old, some new) are really really uglky.

I get the feeling that the whole thing with deny_write_access and
mapping_map_writable could possibly be done after-the-fact somehow as
part of actually inserting the vma in the vma tree, rather than done
as the vma is prepared.

And most users of vma_set_file() probably really don't want that whole
thing at all (ie the DRM stuff that just switches out a local thing.
They also don't check for the new error cases you've added.

So I really think this is quite questionable, and those cases should
probably have been done entirely inside ovlfs rather than polluting
the cases that don't care and don't check.

                 Linus