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From: David Hildenbrand <david@redhat.com>
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Subject: [PATCH v1 08/18] mm/huge_memory: use folio_mapcount() in zap_huge_pmd() sanity check
Date: Tue,  9 Apr 2024 21:22:51 +0200
Message-ID: <20240409192301.907377-9-david@redhat.com>
In-Reply-To: <20240409192301.907377-1-david@redhat.com>
References: <20240409192301.907377-1-david@redhat.com>
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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@redhat.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