ksm: revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from_tree()"

This reverts commit 3e96b6a2e9ad929a3230a22f4d64a74671a0720b.  General
Protection Fault in rmap_walk_ksm() under memory pressure:
remove_rmap_item_from_tree() needs to take page lock, of course.

Link: https://lkml.kernel.org/r/alpine.LSU.2.11.2105092253500.1127@eggly.anvils
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/ksm.c b/mm/ksm.c
index 6bbe314..2f3aaeb 100644 (file)
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -776,11 +776,12 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
                struct page *page;
 
                stable_node = rmap_item->head;
-               page = get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
+               page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
                if (!page)
                        goto out;
 
                hlist_del(&rmap_item->hlist);
+               unlock_page(page);
                put_page(page);
 
                if (!hlist_empty(&stable_node->hlist))