From: Oleg Nesterov <oleg@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>,
Hugh Dickins <hughd@google.com>,
Kirill Shutemov <kirill.shutemov@linux.intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Pavel Emelyanov <xemul@parallels.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/3] special_mapping_fault() is broken
Date: Sun, 12 Jul 2015 01:43:58 +0200 [thread overview]
Message-ID: <20150711234358.GA958@redhat.com> (raw)
In-Reply-To: <20150710145212.4440052265c4f6e074d1f391@linux-foundation.org>
On 07/10, Andrew Morton wrote:
>
> On Fri, 10 Jul 2015 18:51:21 +0200 Oleg Nesterov <oleg@redhat.com> wrote:
>
> > special_mapping_fault() is absolutely broken. It seems it was always
> > wrong, but this didn't matter until vdso/vvar started to use more than
> > one page.
> >
> > The patches are the same, just 1/3 was re-diffed on top of the recent
> > 6b7339f4c31ad "mm: avoid setting up anonymous pages into file mapping"
> > from Kirill.
> >
> > And after this change vma_is_anonymous() becomes really trivial, it
> > simply checks vm_ops == NULL. However, I do think the helper makes
> > sense. There are a lot of ->vm_ops != NULL checks, the helper makes
> > the caller's code more understandable (self-documented) and this is
> > more grep-friendly.
>
> I'm trying to work out which kernel version(s) this should go into,
> without a lot of success.
>
> What do we think the worst-case effects of the bug?
Ah, I should have mentioned this. And when I re-read my messages I see
that "absolutely broken" looks like "should be fixed asap". Sorry for
confusion.
No, this bug is not serious. Nothing bad can happen from the kernel
perspective. And I doubt that some application will ever unmap/remap
the part of vdso or any other install_special_mapping() user. So this
is just correctness fix. In fact, to me the main problem is that I
was totally confused when I tried to read/understand this code ;)
Oleg.
prev parent reply other threads:[~2015-07-11 23:45 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-10 16:51 [PATCH v2 0/3] special_mapping_fault() is broken Oleg Nesterov
2015-07-10 16:51 ` [PATCH v2 1/3] mm: introduce vma_is_anonymous(vma) helper Oleg Nesterov
2015-07-10 16:51 ` [PATCH v2 2/3] mmap: fix the usage of ->vm_pgoff in special_mapping paths Oleg Nesterov
2015-07-10 16:51 ` [PATCH v2 3/3] mremap: fix the wrong !vma->vm_file check in copy_vma() Oleg Nesterov
2015-07-10 17:08 ` [PATCH v2 0/3] special_mapping_fault() is broken Kirill A. Shutemov
2015-07-10 18:20 ` Davidlohr Bueso
2015-07-10 21:52 ` Andrew Morton
2015-07-11 23:43 ` Oleg Nesterov [this message]
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