linux-kernel - [PATCH] ksm: Revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from

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Date:   Sun, 9 May 2021 22:59:34 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Hugh Dickins <hughd@...gle.com>, Miaohe Lin <linmiaohe@...wei.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH] 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.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
---

 mm/ksm.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- 5.13-rc1/mm/ksm.c	2021-05-09 17:03:44.010422188 -0700
+++ linux/mm/ksm.c	2021-05-09 22:12:39.403008350 -0700
@@ -776,11 +776,12 @@ static void remove_rmap_item_from_tree(s
 		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))