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imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=NbOi7s5I; spf=pass (imf04.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=1788783988; b=E1ZWp1RlKw9k0Cciwo9kZjvVyXn31n/igWYpn4012dvbpmjgu3uT/LKBKLqR5rpFdnwmoX L95tvSOsq5r4GcwVLcU+9PRZK0F8LFMEoYzsI8k3M0FLsNCe4liZta/qWjtothVOs/Zx4D XswrcUMWi031sZr3eIfzoVfw8Z1ZgDo= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id F301B4042E; Mon, 7 Sep 2026 12:26:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B3ECF1F00A3A; Mon, 7 Sep 2026 12:26:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788783986; bh=NmJWK+cr7rKoVtR7nNls8ZjI59fsyuTGnN7RsLAmRR4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=NbOi7s5IHW6xh2Ss0fhtBjh+tknCeJlWcd+tDb47dOS1YBw8HZxw9Rdbw42Kk33lQ m7RcqFgb5OBG4vY3PS3Z8zy+Zq9t7UFnbHpyczfnIcUWACwKaxTfSe4ixmvgFg7Tgn ewdBlK8cl5k5gD75k4kEYt/EDgYaraYT3At+5HyprlYiCNtaWbttdV93dH+IYSklKr 0LQxIQDhWx+7Xzd5bnVDAF0e/H+Fo6ZvkXBhvfAz9FiEtHzabFP+LE4G+n0e/jKLb7 p6FlAW5qCCOH+x2/mFc9olTsEqIrkdhzME7jUIL5vV8hIMfYmkBno2+9jixCsKmKUq MZ3HCVJGwqd0g== Message-ID: <087d76fd-0e1c-485e-bccb-e3ce074439cb@kernel.org> Date: Mon, 7 Sep 2026 14:26:21 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/3] mm: khugepaged: fix folio is used after pte_unmap_unlock() To: Vernon Yang , akpm@linux-foundation.org, ljs@kernel.org Cc: nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, zokeefe@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Vernon Yang References: <20260828055926.346744-1-vernon2gm@gmail.com> <20260828055926.346744-3-vernon2gm@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: k4zfnfc4pcg3qqorc9k4r3qzui5cxka7 X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2398B4000D X-Rspam-User: X-HE-Tag: 1788783987-218800 X-HE-Meta: U2FsdGVkX1/ERh2Ua5EHqKYkjGFXcI8Dxk89jPLUc5dNtvwJm6ap7HG487qeEdbnVim/liTVLLXMcuveLsfRA5ptghUFvTEUNKIdxm9DtB1EMyeApDpUNIHYT62ngRvtKhP1utC9G51mNQB/xYAlDcQxfgGJa2DcLGyTcH0d4uHF+wGvMzhsBSp0u4GyIg8dJU+Rvp5UE7eb8DXKHvOs0rErna2xptxj0gVggl11/VC0hJuYEj8ipSIoMq4Wc9YptKimod85bkMAeVCGfXTLgGebsGof/Fy1rvnSGM3Idsvxv8bZhvY1eK+ClR19x0+pJcvyaegARG0DjHw/lFL+F6e0A+5BQbtCmW2DYYRt4qDOMmH/TYLw3OeJnoRof9oeX15JY7PSuCjEaxjmARAMV9+Q+nInqHcEBE3Xi7raNYqq/KADsl8EU8Q67An/aKZiT1sxPBjZLyCzU9wQYYY439cuZph0fOVTLWxYfutCr5ViMXjd4FnML0Xq4JNPkkVqQDrmQimPAteBwz500TAcn9jpGv3fuAieSsCXMoad39j6kAfgd812sQncj0xfOuLQsP7nqq94DRw77CzOnbmrPmarnzXAtl8ejmMrl6DyJMT96IWtGhLYu3ZygKL/KQjCB9Pw1YzuezLfPMMmYYgDtdJ4OzAs+yB1NG/VwQJEAXC6A+da0P1NF14h/1LuIctuaB/qyC/klQtwihZv4z7vIBh+yP2UK1TsbcnHLoScfcjEEjEc7jxdYQ0BkWm76enxnx/ufT2CsSP4hA+Zofy8yoooBFk27Rj1EAXIdwX9S2LlK0Y5WYlRoTJOP11TWRYWcWgoLel9oTMnHgJr8629/iFVM97ywlvNLVlGofRCu521nsVoL3mN4Wch0GQtwTdk4qqrvXM6C/SRuQWDZiamVze+4i/mb+rbnl4gEhrgDdFT+gCdGBLjYrqozBqMAlx7EtmhnXOeU8bfBpzZHH9 sVeOFvj/ 3d2+04Rq7qbQuEko9vTc/v7qv+2HgBvXFoeYZFLBH4g4lmNE4uxFkwbSR1NaCXGQv/G3A4OghY4HRrlQ7HMYYeBhDbgdi4Z3qTF55N5I3EkmacgVNnkd7/UMB9VLtfVkNaCaAXhJTei8OIRKV54Abh7GRoJpw1TU8Psk7QKkRNgeEFG1RJ4IwGAJ6lKx+dPg/jrrCoveghZmln3UxRZC7JKouDmPCv8iWUmAVQd9wonS5B6KmoSo50idmUaJnUkOKIgQrcCMaI1SIZ6fszciPYn5TbGeZezP9Euo7ze7hK+JroQoM3vBSpn9n6TC2zVQ/WarCN6p89vDSDmk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/28/26 07:59, Vernon Yang wrote: > From: Vernon Yang > > After the page table lock has dropped, the folio can be freed > concurrently. The trace_mm_khugepaged_scan_pmd() is left with > a dangling folio pointer. > > So using the folio_pfn() before dropping the page table lock, closing > use-after-free window. > > And other pre-existing bug, When the `for (i = 0; i < HPAGE_PMD_NR; i++)` > iteration to terminate and the folio operation preceding is normal, but > pfn will be incorrect. so we really only trace the PFN if it really was > problematic. > > About calling the respective trace_xxx() functions separately on success > and failure, refer to [1]. > > [1] https://lore.kernel.org/linux-mm/ao6jVbVHLUmuY2UA@gremlin/ > > Acked-by: Lorenzo Stoakes (ARM) > Fixes: 7d2eba0557c1 ("mm: add tracepoint for scanning pages") > Cc: stable@vger.kernel.org > Signed-off-by: Vernon Yang > --- > include/trace/events/huge_memory.h | 6 +++--- > mm/khugepaged.c | 17 ++++++++++++++--- > 2 files changed, 17 insertions(+), 6 deletions(-) > > diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h > index 7b526528f85b..fa828967e1fb 100644 > --- a/include/trace/events/huge_memory.h > +++ b/include/trace/events/huge_memory.h > @@ -55,10 +55,10 @@ SCAN_STATUS > > TRACE_EVENT(mm_khugepaged_scan_pmd, > > - TP_PROTO(struct mm_struct *mm, struct folio *folio, > + TP_PROTO(struct mm_struct *mm, unsigned long pfn, > int referenced, int none_or_zero, int status, int unmapped), > > - TP_ARGS(mm, folio, referenced, none_or_zero, status, unmapped), > + TP_ARGS(mm, pfn, referenced, none_or_zero, status, unmapped), > > TP_STRUCT__entry( > __field(struct mm_struct *, mm) > @@ -71,7 +71,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd, > > TP_fast_assign( > __entry->mm = mm; > - __entry->pfn = folio ? folio_pfn(folio) : -1; > + __entry->pfn = pfn; > __entry->referenced = referenced; > __entry->none_or_zero = none_or_zero; > __entry->status = status; > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index b597a3e68606..4d360ae87769 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1612,6 +1612,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > enum scan_result result = SCAN_FAIL; > struct page *page = NULL; > struct folio *folio = NULL; > + unsigned long failed_pfn = -1; > unsigned long addr; > unsigned long enabled_orders; > spinlock_t *ptl; > @@ -1706,11 +1707,13 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > if (cc->is_khugepaged && !(vma->vm_flags & VM_DROPPABLE) && > folio_test_lazyfree(folio) && !pte_dirty(pteval)) { > result = SCAN_PAGE_LAZYFREE; > + failed_pfn = folio_pfn(folio); > goto out_unmap; > } > > if (!folio_test_anon(folio)) { > result = SCAN_PAGE_ANON; > + failed_pfn = folio_pfn(folio); > goto out_unmap; > } > > @@ -1721,6 +1724,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > if (folio_maybe_mapped_shared(folio)) { > if (++shared > max_ptes_shared) { > result = SCAN_EXCEED_SHARED_PTE; > + failed_pfn = folio_pfn(folio); > count_collapse_event(HPAGE_PMD_ORDER, THP_SCAN_EXCEED_SHARED_PTE, > MTHP_STAT_COLLAPSE_EXCEED_SHARED); > goto out_unmap; > @@ -1738,15 +1742,18 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > node = folio_nid(folio); > if (collapse_scan_abort(node, cc)) { > result = SCAN_SCAN_ABORT; > + failed_pfn = folio_pfn(folio); > goto out_unmap; > } > cc->node_load[node]++; > if (!folio_test_lru(folio)) { > result = SCAN_PAGE_LRU; > + failed_pfn = folio_pfn(folio); > goto out_unmap; > } > if (folio_test_locked(folio)) { > result = SCAN_PAGE_LOCK; > + failed_pfn = folio_pfn(folio); > goto out_unmap; > } > > @@ -1759,6 +1766,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > */ > if (folio_expected_ref_count(folio) != folio_ref_count(folio)) { > result = SCAN_PAGE_COUNT; > + failed_pfn = folio_pfn(folio); > goto out_unmap; > } > > @@ -1782,10 +1790,13 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, > unmapped, cc, enabled_orders); > /* mmap_lock was released above, set lock_dropped */ > *lock_dropped = true; > - } > + trace_mm_khugepaged_scan_pmd(mm, -1, referenced, none_or_zero, > + SCAN_SUCCEED, unmapped); > + } else { > out: > - trace_mm_khugepaged_scan_pmd(mm, folio, referenced, > - none_or_zero, result, unmapped); > + trace_mm_khugepaged_scan_pmd(mm, failed_pfn, referenced, > + none_or_zero, result, unmapped); > + } > return result; > } > Same thought Acked-by: David Hildenbrand (Arm) -- Cheers, David