linux-kernel - [PATCH v1 08/18] mm/huge_memory: use folio_mapcount() in zap_huge

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Date: Tue,  9 Apr 2024 21:22:51 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	linux-doc@...r.kernel.org,
	cgroups@...r.kernel.org,
	linux-sh@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Peter Xu <peterx@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Yin Fengwei <fengwei.yin@...el.com>,
	Yang Shi <shy828301@...il.com>,
	Zi Yan <ziy@...dia.com>,
	Jonathan Corbet <corbet@....net>,
	Hugh Dickins <hughd@...gle.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Rich Felker <dalias@...c.org>,
	John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
	Chris Zankel <chris@...kel.net>,
	Max Filippov <jcmvbkbc@...il.com>,
	Muchun Song <muchun.song@...ux.dev>,
	Miaohe Lin <linmiaohe@...wei.com>,
	Naoya Horiguchi <naoya.horiguchi@....com>,
	Richard Chang <richardycc@...gle.com>
Subject: [PATCH v1 08/18] mm/huge_memory: use folio_mapcount() in zap_huge_pmd() sanity check

We want to limit the use of page_mapcount() to the places where it is
absolutely necessary. Let's similarly check for folio_mapcount() underflows
instead of page_mapcount() underflows like we do in
zap_present_folio_ptes() now.

Instead of the VM_BUG_ON(), we should actually be doing something like
print_bad_pte(). For now, let's keep it simple and use WARN_ON_ONCE(),
performing that check independently of DEBUG_VM.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d8d2ed80b0bf..68ac27d229ef 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1851,7 +1851,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 
 			folio = page_folio(page);
 			folio_remove_rmap_pmd(folio, page, vma);
-			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
+			WARN_ON_ONCE(folio_mapcount(folio) < 0);
 			VM_BUG_ON_PAGE(!PageHead(page), page);
 		} else if (thp_migration_supported()) {
 			swp_entry_t entry;
-- 
2.44.0