linux-kernel - [PATCH v3 01/12] mm: page_alloc: remove pcppage migratetype caching fix

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Date:   Fri, 15 Sep 2023 15:15:34 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Muchun Song <songmuchun@...edance.com>,
        Joao Martins <joao.m.martins@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Hildenbrand <david@...hat.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Rientjes <rientjes@...gle.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Xiongchun Duan <duanxiongchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH v3 01/12] mm: page_alloc: remove pcppage migratetype caching fix

From: Johannes Weiner <hannes@...xchg.org>

Mike reports the following crash in -next:

[   28.643019] page:ffffea0004fb4280 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x13ed0a
[   28.645455] flags: 0x200000000000000(node=0|zone=2)
[   28.646835] page_type: 0xffffffff()
[   28.647886] raw: 0200000000000000 dead000000000100 dead000000000122 0000000000000000
[   28.651170] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[   28.653124] page dumped because: VM_BUG_ON_PAGE(is_migrate_isolate(mt))
[   28.654769] ------------[ cut here ]------------
[   28.655972] kernel BUG at mm/page_alloc.c:1231!

This VM_BUG_ON() used to check that the cached pcppage_migratetype set
by free_unref_page() wasn't MIGRATE_ISOLATE.

When I removed the caching, I erroneously changed the assert to check
that no isolated pages are on the pcplist. This is quite different,
because pages can be isolated *after* they had been put on the
freelist already (which is handled just fine).

IOW, this was purely a sanity check on the migratetype caching. With
that gone, the check should have been removed as well. Do that now.

Reported-by: Mike Kravetz <mike.kravetz@...cle.com>
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 mm/page_alloc.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 123494dbd731..1400e674ab86 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1227,9 +1227,6 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 			count -= nr_pages;
 			pcp->count -= nr_pages;
 
-			/* MIGRATE_ISOLATE page should not go to pcplists */
-			VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
-
 			__free_one_page(page, pfn, zone, order, mt, FPI_NONE);
 			trace_mm_page_pcpu_drain(page, order, mt);
 		} while (count > 0 && !list_empty(list));
-- 
2.41.0