The patch titled
Subject: Revert "mm/rmap.c: reuse mergeable anon_vma as parent when fork"
has been added to the -mm tree. Its filename is
revert-mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/revert-mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/revert-mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch
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------------------------------------------------------
From: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
Subject: Revert "mm/rmap.c: reuse mergeable anon_vma as parent when fork"
This reverts commit 4e4a9eb921332b9d1 ("mm/rmap.c: reuse mergeable
anon_vma as parent when fork").
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()".
Link: http://lkml.kernel.org/r/1581150928-3214-3-git-send-email-lixinhai.lxh@xxxxxxxxx
Fixes: 4e4a9eb92133 ("mm/rmap.c: reuse mergeable anon_vma as parent when fork")
Signed-off-by: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 13 -------------
1 file changed, 13 deletions(-)
--- a/mm/rmap.c~revert-mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork
+++ a/mm/rmap.c
@@ -269,19 +269,6 @@ int anon_vma_clone(struct vm_area_struct
{
struct anon_vma_chain *avc, *pavc;
struct anon_vma *root = NULL;
- struct vm_area_struct *prev = dst->vm_prev, *pprev = src->vm_prev;
-
- /*
- * If parent share anon_vma with its vm_prev, keep this sharing in in
- * child.
- *
- * 1. Parent has vm_prev, which implies we have vm_prev.
- * 2. Parent and its vm_prev have the same anon_vma.
- */
- if (!dst->anon_vma && src->anon_vma &&
- pprev && pprev->anon_vma == src->anon_vma)
- dst->anon_vma = prev->anon_vma;
-
list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
struct anon_vma *anon_vma;
_
Patches currently in -mm which might be from lixinhai.lxh@xxxxxxxxx are
mm-dont-prepare-anon_vma-if-vma-has-vm_wipeonfork.patch
revert-mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch
mm-set-vm_next-and-vm_prev-to-null-in-vm_area_dup.patch
