From: Miaohe Lin linmiaohe@huawei.com
[ Upstream commit c89a384e2551c692a9fe60d093fd7080f50afc51 ]
When removing rmap_item from stable tree, STABLE_FLAG of rmap_item is cleared with head reserved. So the following scenario might happen: For ksm page with rmap_item1:
cmp_and_merge_page stable_node->head = &migrate_nodes; remove_rmap_item_from_tree, but head still equal to stable_node; try_to_merge_with_ksm_page failed; return;
For the same ksm page with rmap_item2, stable node migration succeed this time. The stable_node->head does not equal to migrate_nodes now. For ksm page with rmap_item1 again:
cmp_and_merge_page stable_node->head != &migrate_nodes && rmap_item->head == stable_node return;
We would miss the rmap_item for stable_node and might result in failed rmap_walk_ksm(). Fix this by set rmap_item->head to NULL when rmap_item is removed from stable tree.
Link: https://lkml.kernel.org/r/20210330140228.45635-5-linmiaohe@huawei.com Fixes: 4146d2d673e8 ("ksm: make !merge_across_nodes migration safe") Signed-off-by: Miaohe Lin linmiaohe@huawei.com Cc: Hugh Dickins hughd@google.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/ksm.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/mm/ksm.c b/mm/ksm.c index f51613052aee..cafe00dfdc3b 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -633,6 +633,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) ksm_pages_shared--;
put_anon_vma(rmap_item->anon_vma); + rmap_item->head = NULL; rmap_item->address &= PAGE_MASK;
} else if (rmap_item->address & UNSTABLE_FLAG) {