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authorMiaohe Lin <linmiaohe@huawei.com>2021-05-05 04:37:45 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-05-05 21:27:25 +0300
commitc89a384e2551c692a9fe60d093fd7080f50afc51 (patch)
treea10808c53004b00f08f7f3bdd45fbfa0fb2534eb /mm/ksm.c
parentcd7fae26024690c772ec66719735c58a12034088 (diff)
downloadlinux-c89a384e2551c692a9fe60d093fd7080f50afc51.tar.xz
ksm: fix potential missing rmap_item for stable_node
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>
Diffstat (limited to 'mm/ksm.c')
-rw-r--r--mm/ksm.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index 4b25f642f4ec..e2ba4ebc2500 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -791,6 +791,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
stable_node->rmap_hlist_len--;
put_anon_vma(rmap_item->anon_vma);
+ rmap_item->head = NULL;
rmap_item->address &= PAGE_MASK;
} else if (rmap_item->address & UNSTABLE_FLAG) {