From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 21D83C61DC2 for ; Wed, 26 Aug 2026 07:57:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3171A6B0088; Wed, 26 Aug 2026 03:57:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2C8156B008C; Wed, 26 Aug 2026 03:57:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1B7BA6B0092; Wed, 26 Aug 2026 03:57:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id E5F6A6B0088 for ; Wed, 26 Aug 2026 03:57:14 -0400 (EDT) Received: from smtpin07.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 66DCEA0282 for ; Wed, 26 Aug 2026 07:57:14 +0000 (UTC) X-FDA: 85142665188.07.BF38ADC Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf30.hostedemail.com (Postfix) with ESMTP id 95D2380002 for ; Wed, 26 Aug 2026 07:57:12 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kn+BsycT; spf=pass (imf30.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=1787731032; b=bEkw+APFIiqYXFHEwKUCFYMz+LaJP0qnsfml/rgwNiZqcJTPF80PYjaBl5FRq99ySoZvg3 Z6ok+KnoESS292jk08FoketsZYWTgbEeRuGvQHMfgJt0ROvlDPyTQmXlCvroJO4qBKFfz0 3iHjzM7PCGEEefK5ydASMdtsCblXjQE= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kn+BsycT; spf=pass (imf30.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=1787731032; 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=JoSpfgQVWPrL1xC+VY8JnkH+r+BJbUIhnLuY0YtzjCA=; b=ZgFsV4tSDJW/w4SaJedQwqyJpkFPZpMknqOZkTbYAoEc/ScUcG7rKEskKciyi1BGbYGA13 KU7sYIHh2G3jxAfgr+PsLvpcEpBhHqbTHErqieX2FgQHhlMiKsPW3N1WGebZT9m/+zsM72 5DM8mQYs59yz599SHsTk8a0oZ1ZRxnQ= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id C3A7E41483; Wed, 26 Aug 2026 07:57:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EEECF1F00A3A; Wed, 26 Aug 2026 07:57:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787731031; bh=JoSpfgQVWPrL1xC+VY8JnkH+r+BJbUIhnLuY0YtzjCA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=kn+BsycT04gQ8Z7v7bg784woMyrj3i89HvLmRjTDXrcv9qjJqmPSbDnGUXZGCzLJ/ ie+ALYgFBja7ljDjCXCtXqjGKwBfbhr8XyuW42PRidc7g/D4PI/5yKDesjbZ7RSGdI +7tAytW8JomdXUvRk1Al0ZRYjnre/arA5xMA6W3Z1w9mmHSnMIvOgAW1OhAgasnwGF o9Q6xGSEYUFB3Iv1Hr9ml/HGlawCYbvkrSqCs+vW8Fdh8I27a56Ahin2NnFUm4j2CA smzIOP7F8Kfry1m4/mH4sxuJgHxvnTgd5J5OFdxdUHE18sw971vI52NqMJFNukphKk 51PMIoH44i1Ag== Message-ID: Date: Wed, 26 Aug 2026 09:57:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] mm: khugepaged: fix swap entry value to folio_pfn() To: Vernon Yang Cc: akpm@linux-foundation.org, ljs@kernel.org, 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: <20260824092935.73892-1-vernon2gm@gmail.com> <20260824092935.73892-2-vernon2gm@gmail.com> <6a9c2369-5589-4f2a-bcfe-c6e3b46a1ccd@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <6a9c2369-5589-4f2a-bcfe-c6e3b46a1ccd@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 95D2380002 X-Stat-Signature: 5ygs786s6qkif1ehhqju6aya9h18h4oc X-HE-Tag: 1787731032-862004 X-HE-Meta: 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 AcB2xAtN OI0WLA+tdesr0zcaIwp2R147iNwHyZZxNIFYYGaAFcnRCwkB/PeMrFLvfq7NuzGXUeh/T+ycaUKjMHNVOTxW9i9ZkyewLUZER5IOVGHamDbQ4OF+tywGI6mwBqxuCGw0DdZG+AUkTlsPjLiJWGUIWt0dvWvFSTOs39Dw4VoM74ojUj+SiFVvB5zlirzmDr8AvJDyqSIr0smU0G9Pyndz0+qqmvIbxycPVlL4x24G50Wl2z84srp+2R5QWSPeTrIAfYWc6OyYQLSpkPGnBENM+UYnOyBovFogL/ktBPPIzk5iibgGjWcn1NIcP2R82aY473EXN58u3sZWKWM8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/26/26 04:44, Vernon Yang wrote: > On Mon, Aug 24, 2026 at 01:54:18PM +0200, David Hildenbrand (Arm) wrote: >> On 8/24/26 11:29, Vernon Yang wrote: >>> From: Vernon Yang >>> >>> When the swap entries found exceed max_ptes_swap, the loop is left via >>> break with folio still holding the xarray value that encodes the swap >>> entry, not valid folio pointer. >>> >>> That value is passed to trace_mm_khugepaged_scan_file(), which feeds it >>> to folio_pfn(). On FLATMEM and SPARSEMEM_VMEMMAP, the page_to_pfn() is >>> plain pointer arithmetic, so the trace event merely prints bogus >>> scan_pfn. On classic SPARSEMEM, the page_to_pfn() reads page->flags, >>> dereferencing the tiny encoded integer and oopsing khugepaged whenever >>> the trace event is enabled. >>> >>> So when folio is the swap entry value, simply set pfn to -1, just like >>> exhausted scan naturally. >>> >>> And the folio_put() has maybe dropped the last reference of folio. The >>> trace_mm_khugepaged_scan_file() is left with a dangling folio pointer. >>> so using the folio_pfn() before dropping the reference, closing >>> use-after-free window. >>> >>> Fixes: d41fd2016ed0 ("mm/khugepaged: add tracepoint to hpage_collapse_scan_file()") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Vernon Yang >>> --- >>> include/trace/events/huge_memory.h | 6 +++--- >>> mm/khugepaged.c | 5 ++++- >>> 2 files changed, 7 insertions(+), 4 deletions(-) >>> >>> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h >>> index 5a48c5406cce..7b526528f85b 100644 >>> --- a/include/trace/events/huge_memory.h >>> +++ b/include/trace/events/huge_memory.h >>> @@ -178,10 +178,10 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, >>> >>> TRACE_EVENT(mm_khugepaged_scan_file, >>> >>> - TP_PROTO(struct mm_struct *mm, struct folio *folio, struct file *file, >>> + TP_PROTO(struct mm_struct *mm, unsigned long pfn, struct file *file, >>> int present, int swap, int result), >>> >>> - TP_ARGS(mm, folio, file, present, swap, result), >>> + TP_ARGS(mm, pfn, file, present, swap, result), >>> >>> TP_STRUCT__entry( >>> __field(struct mm_struct *, mm) >>> @@ -194,7 +194,7 @@ TRACE_EVENT(mm_khugepaged_scan_file, >>> >>> TP_fast_assign( >>> __entry->mm = mm; >>> - __entry->pfn = folio ? folio_pfn(folio) : -1; >>> + __entry->pfn = pfn; >>> __assign_str(filename); >>> __entry->present = present; >>> __entry->swap = swap; >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index 79effd3f3da4..00337405c0e0 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -2689,6 +2689,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, >>> int present, swap; >>> int node = NUMA_NO_NODE; >>> enum scan_result result = SCAN_SUCCEED; >>> + unsigned long pfn; >>> >>> present = 0; >>> swap = 0; >>> @@ -2719,6 +2720,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, >>> continue; >>> } >>> >>> + pfn = folio_pfn(folio); >>> if (is_pmd_order(folio_order(folio))) { >>> result = SCAN_PTE_MAPPED_HUGEPAGE; >>> /* >>> @@ -2779,7 +2781,8 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, >>> } >>> } >>> >>> - trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result); >>> + trace_mm_khugepaged_scan_file(mm, (!folio || xa_is_value(folio)) ? -1 : pfn, >>> + file, present, swap, result); >>> return result; >>> } >>> >> >> Shouldn't we just reset PFN to -1 at the beginning of the loop (and set it >> initially)? > > When the `xas_for_each()` iteration to terminate and the folio operation > preceding is normal, but pfn will be incorrect. The PFN is only relevant when a folio participated in the failure. Maybe the following would be cleanest? diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 75639298efc27..371ee0b16d10c 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2683,6 +2683,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, int present, swap; int node = NUMA_NO_NODE; enum scan_result result = SCAN_SUCCEED; + unsigned long problematic_pfn = -1; present = 0; swap = 0; @@ -2714,6 +2715,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, } if (is_pmd_order(folio_order(folio))) { + problematic_pfn = folio_pfn(folio); result = SCAN_PTE_MAPPED_HUGEPAGE; /* * PMD-sized THP implies that we can only try @@ -2725,6 +2727,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, node = folio_nid(folio); if (collapse_scan_abort(node, cc)) { + problematic_pfn = folio_pfn(folio); result = SCAN_SCAN_ABORT; folio_put(folio); break; @@ -2732,12 +2735,14 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, cc->node_load[node]++; if (!folio_test_lru(folio)) { + problematic_pfn = folio_pfn(folio); result = SCAN_PAGE_LRU; folio_put(folio); break; } if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) { + problematic_pfn = folio_pfn(folio); result = SCAN_PAGE_COUNT; folio_put(folio); break; @@ -2773,7 +2778,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, } } - trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result); + trace_mm_khugepaged_scan_file(mm, problematic_pfn, file, present, swap, result); return result; } -- Cheers, David