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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7bd258a30cdsm10740717b3.23.2026.04.28.22.08.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Apr 2026 22:08:48 -0700 (PDT) Date: Tue, 28 Apr 2026 22:08:37 -0700 (PDT) From: Hugh Dickins To: Andrew Morton cc: Baolin Wang , Barry Song , David Hildenbrand , Dev Jain , Lance Yang , Liam Howlett , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Nico Pache , Qi Zheng , Ryan Roberts , Suren Baghdasaryan , Zi Yan , linux-mm@kvack.org Subject: [PATCH hotfix] mm: fix pmd_special() fallback to observe huge_zero Message-ID: <74a75b59-2e13-3985-ee99-d5521f39df2a@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: ECA8F100012 X-Stat-Signature: qg485xyzy99p478e93jwhod7n167bj7i X-Rspam-User: X-HE-Tag: 1777439330-558045 X-HE-Meta: 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 9YW4ac9+ I358Ra4c6do9ORAg7EeXstlXlqKgkHP1y9PduvFiZsNAoxiD3C8BqvwA5juTQ2JM1p5oZ7oLO7WWDwnwOLmOWza85oqEIhEb9p7UTM7DuVRYuGOMCIzGHwGFAwxEc36/DjUOD0Sr66PA2EXeDk8JuTsEgVYpORacxXEIenl2+w9yM34+fR2dZe54ORI2zmmwmFgh4QN4tEach9+J1QkcqQzIkb79MhTGwv/24Ym7lhagR9zclWCTCc6jlEILE7oVguaLCJvgF1HOJHhYYoxvoCa6aZel8YNAsdzNuYttxMLXEPJ+ymNTYuyDEipdW2clYlif8aZQGMMB9Oi4fqib4eST1+Td5ygqTcP43khp3s4PsbA+n+x4tgtQ/5OEmKSWqIuizEQE7yvlccZWKJixI+J1WVRzzz/wQrn5bJ4B0AHHsAdRUzSigC/BEEQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On x86 32-bit with THP enabled, zap_huge_pmd() is seen to generate a "WARNING: mm/memory.c:735 at __vm_normal_page+0x6a/0x7d", from the VM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn)); followed by "BUG: Bad rss-counter state"s, then later "BUG: Bad page state"s when reclaim gets to call shrink_huge_zero_folio_scan(). It's as if the _PAGE_SPECIAL bit never got set in the huge_zero pmd: and indeed, whereas pte_special() and pte_mkspecial() are subject to a dedicated CONFIG_ARCH_HAS_PTE_SPECIAL, pmd_special() and pmd_mkspecial() are subject to CONFIG_ARCH_SUPPORTS_PMD_PFNMAP, which is never enabled on any 32-bit architecture. Add CONFIG_ARCH_HAS_PMD_SPECIAL? Perhaps; but I think it's better just to observe the huge_zero pmd in the fallback version of pmd_special(). Fixes: d80a9cb1a64a ("mm/huge_memory: add and use normal_or_softleaf_folio_pmd()") Signed-off-by: Hugh Dickins --- include/linux/mm.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 0b776907152e..3b02ac43bcb7 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3422,7 +3422,7 @@ static inline pte_t pte_mkspecial(pte_t pte) #ifndef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP static inline bool pmd_special(pmd_t pmd) { - return false; + return is_huge_zero_pmd(pmd); } static inline pmd_t pmd_mkspecial(pmd_t pmd) -- 2.51.0