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.
Signed-off-by: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
---
mm/rmap.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/rmap.c b/mm/rmap.c
index 08c56aaf72eb..31ef76180c53 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -413,8 +413,15 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
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);
/*
--
2.18.4
