From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2C1F8606A31F for ; Thu, 29 Oct 2026 20:38:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FIuxTTI3 Received: by kanga.kvack.org (Postfix) id 1AA8F6B05CF; Thu, 29 Oct 2026 16:38:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 182566B05D0; Thu, 29 Oct 2026 16:38:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 09B196B05D1; Thu, 29 Oct 2026 16:38:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id D0AE56B05CF for ; Thu, 29 Oct 2026 16:38:13 -0400 (EDT) Received: from smtpin25.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 58981140519 for ; Thu, 29 Oct 2026 20:38:13 +0000 (UTC) X-FDA: 85376826066.25.41E6E28 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf27.hostedemail.com (Postfix) with ESMTP id 8B7E44000A for ; Thu, 29 Oct 2026 20:38:11 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=FIuxTTI3; spf=pass (imf27.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793306291; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=nj1Bf9db8TNcajGSKnb6DbuHi/phVwkCDM1cIZai6DI=; b=lB8lbiOcJ0jyjxEWwBema1U3AF1J/bsXKJZIy2nKt7oiLjtk34kzJla+8aLeuWz08dV2mf KJSIIyZT/XIhydVMulbhskNNP+uRHcCcEbrlUGeYGo2xKLY755ZuD9XMPuoAUyY2EPE/Dw B07ZTkb/nVC1zvS43y27hRon64SbAa8= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=FIuxTTI3; spf=pass (imf27.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793306291; b=w+gzFIarb6MfTFd8aQylBR+11Nsi/0CzDiSL6cYiYRK+rwSoPxf5bqZVmmcDSHy7JlPNNm Q0VMfoArg0FuY2/9HLceqqpv0MG9sD0T57gwJON2xOK8doujC+d1iGf6Q7nGKPONMwYThy bu2V8d6Es3N8N9wWWXt4zwV/LzCgXrM= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 8A96140F8B; Thu, 29 Oct 2026 20:38:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1BE841F01825; Thu, 29 Oct 2026 20:37:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793306290; bh=nj1Bf9db8TNcajGSKnb6DbuHi/phVwkCDM1cIZai6DI=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=FIuxTTI3C9PGyWVFGo4s1b0dkDlzRfab9Rj6I74MTLycqi+2Em6LiHU/uAvrS9N2K H1lysuB2CyMvu8AUoaV21WSVGPL5xMuFv701vHfyNuvbTOqOVl1Mb27qjgobqyD4Ih w521JBB1DU2+1WGBmfWNyNI9L0QxayWIoR/35/8S6lbTgqbOOCRUYTrMQVyzhih2Uy 5YOZ+Uv9eZAqw/sFSkR0LDJjCsJd17NT85n8UbO6chx+PkSu1BaBgYlPYiLxlSRP0s YNrqZmF/rZnmJY1dOZd/zKWR/IT1NfuAz2jIJEzyiNNCuLG/4f2hBHEDIvx0IURMf/ 8vhdjMEwBOimg== From: "David Hildenbrand (Arm)" Date: Thu, 29 Oct 2026 21:33:14 +0100 Subject: [PATCH v2 19/47] mm/gup: recheck the PUD under PTL in follow_pud_mask() X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261029-fixes_core-v2-19-a64ce7f83abb@kernel.org> References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> In-Reply-To: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> To: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Josef Bacik , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3795; i=david@kernel.org; h=from:subject:message-id; bh=PWJnBAFtWkzROraFyD6718GFghC4dRBvxtyaTiDuAbI=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIer23rib/wxOTO+QCt1Qe9WZRKlh48bPQzJd5VePoC4 U+SnnmGHaUsDGIcDLJiiixBwfcNXr5cV1vtxscMM4eVCWQIAxenAEzEjI2RYcKTwxteKM7pfsr5 l+9Y52+mDR9eFry6cu7nmmdGkT3yTnmMDE90/nzPfmm/TfZaV3vaLZ02o7usjFJSH3c4GdrG75m 0hBUA X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 8B7E44000A X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=4.0.1 X-Stat-Signature: wbda9c8uti1xz4jq9jpb1csoh44r11pc X-HE-Tag: 1793306291-586254 X-HE-Meta: U2FsdGVkX18bFxb2xk7oRdEV1Arbtc7ALAGAIYmTulwDoiBSR0+3N5rCUEYsu9vtnj+RVPFsWkQn1LVK6xq7Otm0lIHNE7zQn+GjUT3sQAMkzXSQxeisjGzmYkzzfGf4CAd3d1Jne+ZCdKghJrd1Fds5V4IQXGwvom3oAt/+ibNl/ELKj9FMkSUpfYF/VBNGHxtJXfkyuLG5NtkvkwKL7rDIgexCx8DQINRzCJV0mYeohZWZyLaUwZdCNWTmVDFjx5yr9E3TnU0QXpBLKplrZ/WgBr/inJBMnk9g5tpjP6P1N8RexyHeWlBlUKIDcmvcV/muViKuJEhN0YYD1YdPUc3WW9z98CCzzzV9Rl3lUCdRh3vEaZSei6SzpGF3YNtQGkJRaY7y5lRym9KapFURB7Ckxg/dFOolDmcpHW7ZNLU0m1zAD59iKTp3D46eih+9EOMwofzbWFFG2HUuBikHmMEITy3niRD+Tpw3l+KNdiX4/zbdhWmFkdLJOtwcqT9Bx+katGWiC2wbfBhBuzE7TY97+r0vneJWTlaUWjWM9tiZrYvxPcWXtXI68sjPRL++qQeozHWluwLzAf1XGoLMmttJGuUI6ti8jSS67Xp7O1tKU1KFE+yFM/uLm4KMN6bFM3l75KGOUWpCv0LM37EFL0PQWhlRKUksCZQoRyTAYdDv+A/m/QJSAPDuwkheh+VgW9jMqRwMyNqocz/u7qNGhlq96rzePsLfv4sNRUD3MAygrthp5Hp1PBgTzcf3zGInhEqwptgQcuZFhMrm8MIR+OwsS/bgaQqzvWnxXMG69VgyPEXcppQ9M/9xOqIO84u1naNsmGG5ISqACEFd0qXHiu/Q8Eun6MDdnDnU5iyquYFKfnkFk1RfYbMqSaXPn04S9+NhQ/tgMatudySg5N112jbs7mECmmEWOCKUnMFnqnKmjO4FuRk6UKiIn2vfyuXopWy6HVQn+OXK/XdxoqR deUD7ySX nOGfEgriKSBU0Ce2gS3iiV4d34BSTl0eAYni0ccuGgr7CR6tRKaBI82q+1i7OFhY+jw31BfQ2iXK3b+aIB6tviZzmLWF3yNqJd9cVkiwz5zYrIvpxdjx2Amt2z8CKCdF5AfK4KS9ew76Vu+2ZdnQU6R/qTVvbe2UIvGlkb/Ldgbmhi1t/caNOQyAIfQ9xexLP9xntWDDzBHnsC6fMsjjUU4dlDQYUcVfVEu4467iCBrK2RKgCwJtvJ2Wz8SIwBJsdy4Cagm7YFAZJq6pPTgLeYDdXi9jCD3afEYZVSgdqIBtNQ51Ixzmw85+SWFHFsLTK2czg5ss0Bx9WFtEbuoVt7FM9p2shrBY84w6X66SrXSgo+R6p8jTDvwIPF3t26dNoVdkQL+PVPm+nHvjzDtvDmMuGm/bzDQ1K2y2bTFxz/kggCWU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 follow_pud_mask() reads the PUD without a lock. If it is a leaf, it takes the lock and calls follow_huge_pud(), which reads the entry again, but only tests whether it is present. A leaf can be zapped concurrently and a page fault can fill the empty entry with a page table. This currently only applies when device-dax makes use of PUD entries, and the fault after e.g., MADV_DONTNEED would find THPs to be disabled. That requires a sequence like 1) Fault in the PUD 2) Disable THP 3) Have GUP race against concurrent MADV_DONTNEED + refault Which is rather unlikely to happen in practice, which is why we never received a report about such a problem. Before commit 1b1676180246 ("mm/gup: handle huge pud for follow_pud_mask()"), we performed that check in follow_devmap_pud() by testing for pud_devmap(). Let's fix it by just structuring follow_pud_mask() similar to follow_pmd_mask(), minus protnone stuff that does not apply and minus FOLL_SPLIT_PMD handling. That makes it much easier to spot any such inconsistencies. Perform the pud_bad() check early in follow_pmd_mask() and just forward the PUD value. We can drop the pud_present() check in follow_huge_pud(), just like we have in follow_huge_pmd(). Even though we are performing more changes than strictly necessary, the fix should be easy to backport. Fixes: 1b1676180246 ("mm/gup: handle huge pud for follow_pud_mask()") Cc: stable@vger.kernel.org Reported-by: Josef Bacik Signed-off-by: David Hildenbrand (Arm) --- mm/gup.c | 32 ++++++++++++++++++-------------- 1 file changed, 18 insertions(+), 14 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 7d43ce717b24..f809361227e7 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -658,9 +658,6 @@ static struct page *follow_huge_pud(struct vm_area_struct *vma, assert_spin_locked(pud_lockptr(mm, pudp)); - if (!pud_present(pud)) - return NULL; - if ((flags & FOLL_WRITE) && !can_follow_write_pud(pud, pfn_to_page(pfn), vma, flags)) return NULL; @@ -896,15 +893,17 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, } static struct page *follow_pmd_mask(struct vm_area_struct *vma, - unsigned long address, pud_t *pudp, - unsigned int flags, - unsigned long *page_mask) + unsigned long address, pud_t *pudp, pud_t pud, + unsigned int flags, unsigned long *page_mask) { pmd_t *pmd, pmdval; spinlock_t *ptl; struct page *page; struct mm_struct *mm = vma->vm_mm; + if (unlikely(pud_bad(pud))) + return no_page_table(vma, flags, address); + pmd = pmd_offset(pudp, address); pmdval = pmdp_get_lockless(pmd); if (pmd_none(pmdval)) @@ -953,18 +952,23 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma, pud = pudp_get(pudp); if (!pud_present(pud)) return no_page_table(vma, flags, address); - if (pud_leaf(pud)) { - ptl = pud_lock(mm, pudp); - page = follow_huge_pud(vma, address, pudp, flags, page_mask); + if (!pud_leaf(pud)) + return follow_pmd_mask(vma, address, pudp, pud, flags, page_mask); + + ptl = pud_lock(mm, pudp); + pud = *pudp; + if (unlikely(!pud_present(pud))) { spin_unlock(ptl); - if (page) - return page; return no_page_table(vma, flags, address); } - if (unlikely(pud_bad(pud))) - return no_page_table(vma, flags, address); + if (unlikely(!pud_leaf(pud))) { + spin_unlock(ptl); + return follow_pmd_mask(vma, address, pudp, pud, flags, page_mask); + } - return follow_pmd_mask(vma, address, pudp, flags, page_mask); + page = follow_huge_pud(vma, address, pudp, flags, page_mask); + spin_unlock(ptl); + return page; } static struct page *follow_p4d_mask(struct vm_area_struct *vma, -- 2.43.0