linux-kernel - [PATCH 1/2] mm/page_alloc: Always remove pages from temporary list

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Message-Id: <20221118101714.19590-2-mgorman@techsingularity.net>
Date:   Fri, 18 Nov 2022 10:17:13 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: [PATCH 1/2] mm/page_alloc: Always remove pages from temporary list

free_unref_page_list() has neglected to remove pages properly from the list
of pages to free since forever. It works by coincidence because list_add
happened to do the right thing adding the pages to just the PCP lists.
However, a later patch added pages to either the PCP list or the zone list
but only properly deleted the page from the list in one path leading to
list corruption and a subsequent failure. As a preparation patch, always
delete the pages from one list properly before adding to another.  On its
own, this fixes nothing although it adds a fractional amount of overhead
but is critical to the next patch.

Reported-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/page_alloc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 218b28ee49ed..1ec54173b8d4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3546,6 +3546,8 @@ void free_unref_page_list(struct list_head *list)
 	list_for_each_entry_safe(page, next, list, lru) {
 		struct zone *zone = page_zone(page);

+		list_del(&page->lru);
+
 		/* Different zone, different pcp lock. */
 		if (zone != locked_zone) {
 			if (pcp)
-- 
2.35.3