The patch titled Subject: Revert "mm/rmap.c: reuse mergeable anon_vma as parent when fork" has been removed from the -mm tree. Its filename was revert-mm-rmapc-reuse-mergeable-anon_vma-as-parent-when-fork.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ 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. Reusing anon_vma within the process is fine. But if a vma has gone through fork(), then that vma's anon_vma should not be shared with its neighbor vma. As explained in [1], when vma gone through fork(), the check for list_is_singular(vma->anon_vma_chain) will be false, and don't share anon_vma. With current issue, one example can clarify more. Parent process do below two steps: 1. p_vma_1 is created and p_anon_vma_1 is prepared; 2. p_vma_2 is created and share p_anon_vma_1; (this is allowed, becaues p_vma_1 didn't gothrough fork()); parent process do fork(): 3. c_vma_1 is dup from p_vma_1, and has its own c_anon_vma_1 prepared; at this point, c_vma_1->anon_vma_chain has two items, one for p_anon_vma_1 and one for c_anon_vma_1; 4. c_vma_2 is dup from p_vma_2, it is not allowed to share c_anon_vma_1, because c_vma_1->anon_vma_chain has two items. [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 @@ -275,19 +275,6 @@ 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