From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794272942; b=FUmouuX1Dfof0ZjlfWzIuwxw50+fGaSXazeEdytrzA5+u76KEKzNTpnYIqXfd5+CG1tc oiDH7645qGiTip8lOQdaqNuBZgb09n3a7tSd3Cs7PLxYi6uWZ0dRBnhrj47O3VHlENk3o XOjePGXDkDq3R7qEoBFx2HfFF6xdB2zM4iJOvCOJuhLoquw66zUevNGGr+AwrU1Vk/lbx 1PH07hL95Y04/fqaJtBum1rmLosQNFUXwudl/RediTs3xnwpAtWgrfzMCEwQSn7uAnVgU OLfCCe0Mo10G0WFdYVV8IAiFH91U8oazloCGDYMEIyzWYMSI4WA/f3nYkBFgE9uJUcw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794272942; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=tABhjbrUjpLXekCgxWiyuiENONr9Z4Nj9Pviai1roBA=; b=GSjlbT5T7UYkzOxnw/kBtOLFcMqLuwx9LX+XNHyUppqDAfHuIYBYVzNFbqcs+sZduFNo jBY+9mDZzljsAn1pY4CNSCf/leQLuZUTCNbUqXqlUCc07PxldBk9vK0DST6ctkhe8MgNb sHKj82gKiNthP3TTgvtBHq2sarSNNCXx2LCdb90MDWjqTEpIrWBE4mj1oCnWrZ1fZXlc0 dt3nIfDvPtRnFZa++e5P3d7tL3kRmbkkuG9e9nw0789kjLSt4qzb2Q9k2llQItbCq849I HzvbvcuKhxlb5VJJDcHTeYLwykYOPvA8TiGtV4tOYLPneVt8kFLXHsW2ovEXPxG5JGQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Ryi8nV+3; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9BD61606A32A for ; Tue, 10 Nov 2026 01:09:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Ryi8nV+3 Received: by smtp.kernel.org (Postfix) with ESMTPSA id F081C1F0089F; Tue, 10 Nov 2026 01:09:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794272942; bh=tABhjbrUjpLXekCgxWiyuiENONr9Z4Nj9Pviai1roBA=; h=From:To:Cc:Subject:Date; b=Ryi8nV+3hjsz2p8F/gknpPwDdmQAlRpXv4Sp9jzfKPFA0RLRztGO0RMJDJLMbvwbz x8Su2ZDOqd1NiNZ0QpniOpCM4Ghkd3GeMiF/wAdwWHWHUN5v7eCClc4ut96+c95ub8 NEpZorsWlPaMX1uyDoDaCgDqPZ+oVuZPXV6ZFRsl7KCTcd8bOuwNk8laV5OTWEjBBM DEWjpgWNfhTruRYYMoSG0FGY1wjRkPBD1UNy+ub/cVtT2E0xkOuWxlJLNhlAX8T1od ZUb7u92blhXtDqYh86y6KNhjCMCsmc5/eKnH3/zg3BgQyFNwdXqZTb+SokEmqRDYvk ecGZ2pm2WRsew== From: Sasha Levin To: david@kernel.org, josef@toxicpanda.com, usama.anjum@arm.com Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] mm/gup: recheck the PUD under PTL in follow_pud_mask()" failed to apply to 6.12-stable tree Date: Mon, 9 Nov 2026 20:09:00 -0500 Message-ID: <20261109200900-failed-6.12-79cb51d538ab@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 79cb51d538abc459f74e046d27797d36b133ce0e # git commit -s git send-email --to '' --in-reply-to '20261109200900-failed-6.12-79cb51d538ab@kernel.org' --subject-prefix 'PATCH 6.12.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 79cb51d538abc459f74e046d27797d36b133ce0e Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:39:48 +0100 Subject: [PATCH] mm/gup: recheck the PUD under PTL in follow_pud_mask() 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 Tested-by: Muhammad Usama Anjum Link: https://patch.msgid.link/20261031-fixes_core-v3-19-d6437171ecc3@kernel.org 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 7d43ce717b246..f809361227e7e 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, -- 2.53.0