From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AF92C3D9027 for ; Wed, 30 Sep 2026 19:02:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790794927; cv=none; b=Kvp+AQb/ONemxJFfS2QUlMYwnrfUXJ6AoZzbG7yhopXqAgNeu2no1yO5CQ8KD2y3vqBh62o3uCbP1oUHQi3cz/q5AyKHiGNHi1pq5zPrQyXvcSH/3r6/gGwHwL7v3Wc0TexJL+//LbHxzXIDiVc/s80SAcbpeHX1UVO9V8fIv7U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790794927; c=relaxed/simple; bh=XRIWCs2N3Mc1B+K/qR/2mHPXLrrKVNsSqcBkAEaDd4Y=; h=Date:To:From:Subject:Message-Id; b=ayimMFpGmBdkubGMQDE7a1bM2ehxaAMTn8OEQ9iLKgKWiZAB13GrUkqT1USoZ3PwuGoZXjeV76koljWUTAqW0AEoq8nDmsiKLZBaORhrqS/4JlXD+Lih1P3X/Nj4RsKHCzz3BdtyeHP0rtGcTTorf7ArqvCgElOj//D67NXtdDo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=nOXxCWn+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="nOXxCWn+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68D061F00898; Wed, 30 Sep 2026 19:02:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790794925; bh=Kcj3QTNFWpHw2Io16TVL7LYIME57gl+3bFN6wsEaH0c=; h=Date:To:From:Subject; b=nOXxCWn+GizCbPuEx5h+XZpA6T9ZPLPX+t4FlUnvO1qbawAbYmh92tgMgcI82fSFa PFK40RTY6jSWF4Zq+8fi3zJRuv3kQ4LgJyVmvkQZE6L5M4JcXiDBXlcl4Vw59zNHKL JycOvJMYcbdQfB1KM0IpljayS3eMsRd4ffTJhmQo= Date: Wed, 30 Sep 2026 12:02:05 -0700 To: mm-commits@vger.kernel.org,muchun.song@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch added to mm-unstable branch Message-Id: <20260930190205.68D061F00898@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: fixup! powerpc/mm: switch device DAX to shared tail vmemmap pages has been added to the -mm mm-unstable branch. Its filename is powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Muchun Song Subject: fixup! powerpc/mm: switch device DAX to shared tail vmemmap pages Date: Wed, 30 Sep 2026 23:28:26 +0800 The PowerPC radix path takes one reference for every PTE that maps the shared tail page. Unlike the generic path, get_page() lets the counter continue after it becomes non-positive and eventually cycle to zero. Use try_get_page() so vmemmap population fails before the shared page reference count can cycle, matching the generic implementation. Link: https://lore.kernel.org/20260930152826.76084-1-songmuchun@bytedance.com Signed-off-by: Muchun Song Signed-off-by: Andrew Morton Cc: David Hildenbrand Cc: Oscar Salvador Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Jonathan Corbet Cc: Lorenzo Stoakes Cc: Mike Rapoport Cc: Qi Zheng Cc: Nicholas Piggin Cc: Christophe Leroy Cc: Ritesh Harjani (IBM) Cc: Shrikanth Hegde Cc: Randy Dunlap Cc: Lance Yang --- arch/powerpc/mm/book3s64/radix_pgtable.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/arch/powerpc/mm/book3s64/radix_pgtable.c~powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages-fix +++ a/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -1042,13 +1042,17 @@ static pte_t * __meminit radix__vmemmap_ /* * When a PTE/PMD entry is freed from the init_mm * there's a free_pages() call to this page allocated - * above. Thus this get_page() is paired with the + * above. Thus this try_get_page() is paired with the * put_page_testzero() on the freeing path. * This can only called by certain ZONE_DEVICE path, * and through vmemmap_populate_compound_pages() when * slab is available. + * + * Use try_get_page() to prevent the shared page refcount + * from overflowing. */ - get_page(reuse); + if (!try_get_page(reuse)) + return NULL; p = page_to_virt(reuse); pr_debug("Tail page reuse vmemmap mapping\n"); } _ Patches currently in -mm which might be from muchun.song@linux.dev are mm-sparse-vmemmap-factor-out-shared-vmemmap-tail-page-allocation.patch mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically.patch mm-sparse-vmemmap-introduce-config_vmemmap_optimization.patch mm-sparse-vmemmap-open-code-init_compound_tail.patch mm-sparse-vmemmap-prepare-dax-vmemmap-population-for-compound-page-orders.patch mm-sparse-vmemmap-set-compound-page-order-for-device-dax.patch mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages.patch mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch mm-sparse-vmemmap-drop-unused-section_nr_vmemmap_pages-arguments.patch documentation-mm-update-dax-vmemmap-deduplication-docs.patch mm-sparse-vmemmap-drop-vmemmap_populate_dax.patch mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path.patch mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch mm-sparse-vmemmap-remove-the-unused-ptpfn-argument.patch mm-sparse-vmemmap-open-code-vmemmap_populate_address.patch mm-mm_init-add-zone-mismatch-warning-during-page-init.patch