From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Li Xinhai <lixinhai.lxh@gmail.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Matthew Wilcox <willy@infradead.org>,
Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH 2/3] Revert "mm/rmap.c: reuse mergeable anon_vma as parent when fork"
Date: Thu, 2 Apr 2020 16:59:22 +0300 [thread overview]
Message-ID: <20200402135922.kcllgas7omuyn5h7@box> (raw)
In-Reply-To: <1581150928-3214-3-git-send-email-lixinhai.lxh@gmail.com>
On Sat, Feb 08, 2020 at 08:35:27AM +0000, Li Xinhai wrote:
> This reverts commit 4e4a9eb921332b9d1edd99f76998f99f36b195f7
> In dup_mmap(), anon_vma_fork() is called for attaching anon_vma and
> parameter 'tmp' (i.e., the new vma of child) has same ->vm_next and
> ->vm_prev as its parent vma. That causes the anon_vma used by parent been
> mistakenly shared by child (In anon_vma_clone(), the code added by that
> commit will do this reuse work).
>
> Besides this issue, the design of reusing anon_vma from vma which has
> gone through fork should be avoided ([1]). So, this patch reverts that
> commit and maintains the consistent logic of reusing anon_vma for
> fork/split/merge vma.
>
> [1] commit d0e9fe1758f2 ("Simplify and comment on anon_vma re-use for
> anon_vma_prepare()") explains the test of "list_is_singular()".
I read the description few time, but I cannot say I understood the
problem completely. Do you have a test-case to demonstrate the issue?
IIUC, re-using anon_vma across fork is wrong, but within the process is
fine, right?
Maybe we should just check that dst->vm_mm matches src->vm_mm before
re-using anon_vma?
--
Kirill A. Shutemov
next prev parent reply other threads:[~2020-04-02 13:59 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-08 8:35 [PATCH 0/3] mm: Fix misuse of parent anon_vma in dup_mmap path Li Xinhai
2020-02-08 8:35 ` [PATCH 1/3] mm: don't prepare anon_vma if vma has VM_WIPEONFORK Li Xinhai
2020-02-08 8:53 ` Li Xinhai
2020-04-02 13:45 ` Kirill A. Shutemov
2020-02-08 8:35 ` [PATCH 2/3] Revert "mm/rmap.c: reuse mergeable anon_vma as parent when fork" Li Xinhai
2020-04-02 13:59 ` Kirill A. Shutemov [this message]
2020-04-03 3:08 ` Li Xinhai
2020-04-05 1:26 ` Li Xinhai
2020-02-08 8:35 ` [PATCH 3/3] mm: set vm_next and vm_prev to NULL in vm_area_dup() Li Xinhai
2020-04-02 14:07 ` Kirill A. Shutemov
2020-02-10 0:52 ` [PATCH 0/3] mm: Fix misuse of parent anon_vma in dup_mmap path Andrew Morton
2020-02-10 2:15 ` Li Xinhai
2020-04-20 12:06 ` Michal Hocko
2020-04-21 3:53 ` Li Xinhai
2020-04-21 7:26 ` Michal Hocko
2020-04-02 1:25 ` Andrew Morton
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