The patch titled
Subject: mm: rmap: explicitly reset vma->anon_vma in unlink_anon_vmas()
has been added to the -mm tree. Its filename is
mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch
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------------------------------------------------------
From: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
Subject: mm: rmap: explicitly reset vma->anon_vma in unlink_anon_vmas()
In case the vma will continue to be used after unlink its relevant
anon_vma, we need to reset the vma->anon_vma pointer to NULL. So, later
when fault happen within this vma again, a new anon_vma will be prepared.
By this way, the vma will only be checked for reverse mapping of pages
which been fault in after the unlink_anon_vmas call.
Currently, the mremap with MREMAP_DONTUNMAP scenario will continue use the
vma after moved its page table entries to a new vma. For other scenarios,
the vma itself will be freed after call unlink_anon_vmas.
Link: https://lkml.kernel.org/r/20210119075126.3513154-1-lixinhai.lxh@xxxxxxxxx
Signed-off-by: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/mm/rmap.c~mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas
+++ a/mm/rmap.c
@@ -413,8 +413,15 @@ void unlink_anon_vmas(struct vm_area_str
list_del(&avc->same_vma);
anon_vma_chain_free(avc);
}
- if (vma->anon_vma)
+ if (vma->anon_vma) {
vma->anon_vma->degree--;
+
+ /*
+ * vma would still be needed after unlink, and anon_vma will be prepared
+ * when handle fault.
+ */
+ vma->anon_vma = NULL;
+ }
unlock_anon_vma_root(root);
/*
_
Patches currently in -mm which might be from lixinhai.lxh@xxxxxxxxx are
mm-rmap-explicitly-reset-vma-anon_vma-in-unlink_anon_vmas.patch
mm-mremap-unlink-anon_vmas-when-mremap-with-mremap_dontunmap-success.patch
mm-hugetlbc-fix-unnecessary-address-expansion-of-pmd-sharing.patch
