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 8F4643624A9 for ; Mon, 28 Sep 2026 04:45:11 +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=1790570713; cv=none; b=pL4zZJgmOs/tklqMv0DyMhfqaBQbCjkKJun+drerHkGIDvRLg9bCd86tRx5+lpNRF1XrKfefL4eDPdlF+hNBWhxYCs7pUihUPSoZli4CGste5YDSjZTACZq8dhR+gqZKKFfgA4SiV6qn6F/+fqbJC/EHF2Ix3KqQdBk0qYK6CM0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790570713; c=relaxed/simple; bh=iMHky30dVwt28LZuH0JBMZyVnR22WuFWJHovD3y+DNw=; h=Date:To:From:Subject:Message-Id; b=WVnQWeNibnFNQLpSL8zKYLt2je5gwa5lJRoPd7DkMI9t8CiOhUM7NyeCjFUe8aRTGkBLGFgCYxS9q0nz4ONr/NkoTiHTGn2LSGmgfcv41BbpNJXHGuHTIhDJtAyp1eJUYSdxBIZ9KX8e+D7u1DfrM/QlHEbVQBk+adYBjohOQVs= 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=QZ7z+Sn2; 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="QZ7z+Sn2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E41581F000FF; Mon, 28 Sep 2026 04:45:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790570711; bh=rtmz560vka6+4cvWJF+v1B7c0Vkt689qtlfkxvvQevs=; h=Date:To:From:Subject; b=QZ7z+Sn2km41un1gl69BJCwSGSjrFl9H65eOHoVHf5iZHwsMsuCcL4SuldPrPcqKn P5S1gzEiP3ScWppfIOxFZ9jBEZLunT5Jg1zuHyACxaSVbqX/5hVCbXFgQN/PKNp3/1 ogCQ5GkBnodP5Bzx1y6Vqh4oEkrCVquHK/xBhdtE= Date: Sun, 27 Sep 2026 21:45:10 -0700 To: mm-commits@vger.kernel.org,rppt@kernel.org,rdunlap@infradead.org,qi.zheng@linux.dev,osalvador@suse.de,npiggin@gmail.com,mpe@ellerman.id.au,maddy@linux.ibm.com,ljs@kernel.org,lance.yang@linux.dev,david@kernel.org,corbet@lwn.net,chleroy@kernel.org,muchun.song@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch added to mm-unstable branch Message-Id: <20260928044510.E41581F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix has been added to the -mm mm-unstable branch. Its filename is mm-sparse-vmemmap-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/mm-sparse-vmemmap-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: mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix Date: Mon, 28 Sep 2026 12:41:48 +0800 Each PTE mapping the shared device DAX tail page takes a page reference. A sufficiently large range could therefore cycle the reference count back to zero if population were allowed to continue after it became non-positive. Use try_get_page() so further mappings fail once the reference count is no longer positive. The section population error path tears down mappings created for the failed section, while the warning makes this currently impractical limit visible. Link: https://lore.kernel.org/20260928044148.3300333-1-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: Randy Dunlap Cc: Lance Yang --- mm/sparse-vmemmap.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) --- a/mm/sparse-vmemmap.c~mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages-fix +++ a/mm/sparse-vmemmap.c @@ -286,14 +286,18 @@ static pte_t * __meminit vmemmap_pte_pop /* * 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. */ - if (flags & VMEMMAP_POPULATE_DAX) - get_page(pfn_to_page(ptpfn)); + if ((flags & VMEMMAP_POPULATE_DAX) && + !try_get_page(pfn_to_page(ptpfn))) + return NULL; } entry = pfn_pte(ptpfn, PAGE_KERNEL); set_pte_at(&init_mm, addr, pte, entry); _ 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 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