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 6DE08FB5E97 for ; Tue, 17 Mar 2026 01:05:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6C3A16B0005; Mon, 16 Mar 2026 21:05:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 674876B0088; Mon, 16 Mar 2026 21:05:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 58A786B0089; Mon, 16 Mar 2026 21:05:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 3B0356B0005 for ; Mon, 16 Mar 2026 21:05:02 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id BC153C1CB4 for ; Tue, 17 Mar 2026 01:05:01 +0000 (UTC) X-FDA: 84553760802.10.D937F43 Received: from out30-112.freemail.mail.aliyun.com (out30-112.freemail.mail.aliyun.com [115.124.30.112]) by imf22.hostedemail.com (Postfix) with ESMTP id 9B34FC000B for ; Tue, 17 Mar 2026 01:04:58 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=linux.alibaba.com header.s=default header.b=S4u0coRT; spf=pass (imf22.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.112 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=linux.alibaba.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1773709499; 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=IjQSFS0itEQzM5rr+GWV/Figi9xDYU/T6PhEBKJz3LI=; b=ENa7QY5BB2Vg7F6ZPTeAgnXvxqXFCO8jykHJGApLmCe4FjzFzYJh8LaEFUf/+QjIrRuFqC X38C/OvBFHKawiTvZp91Gqpefmuj8toZEhfSi0XUVALm7spwzmxuE9IpcyR+MPL5Mmz5cc HHSEz/1WsX3tM/R6OQqUyA5JAjwSqB0= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=linux.alibaba.com header.s=default header.b=S4u0coRT; spf=pass (imf22.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.112 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=linux.alibaba.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773709499; a=rsa-sha256; cv=none; b=B10boBRWPpPYKk6h4XDh4A9VNvD+6n6tjYdMxpf2GDbolGsJKbE8dYlwg8g89H/WqoD9Zm mcAHEWZLIeRt+hJU/FwNutwYL51XB1GTzcEjGbZfEl4s/TkuOZIP8XXoAqqiBA7vT6HnLS hTI/150bmK0ynk2ubg3/RFwHkpOIL24= DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1773709495; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=IjQSFS0itEQzM5rr+GWV/Figi9xDYU/T6PhEBKJz3LI=; b=S4u0coRTa7rYbBj+ExX37wMKJe5XpXrcS2A5vi0edayMw1OxU40mP6puk7IOsUU8UHRQxcwridSqoCSD1m9gNqlFNzyqFkxkTgpF6A93kizv2L0fYhc9QLD8VZOQid0bvjNodOKE/z8fwamay2wOjpKq6aApyjgCXy5NxG1xhKw= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R151e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045133197;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=18;SR=0;TI=SMTPD_---0X.9.3Ty_1773709492; Received: from 30.221.57.233(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X.9.3Ty_1773709492 cluster:ay36) by smtp.aliyun-inc.com; Tue, 17 Mar 2026 09:04:53 +0800 Message-ID: Date: Tue, 17 Mar 2026 09:04:52 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: filemap: fix nr_pages calculation overflow in filemap_map_pages() To: Kiryl Shutsemau Cc: Dev Jain , akpm@linux-foundation.org, willy@infradead.org, david@kernel.org, lorenzo.stoakes@oracle.com, p.raghav@samsung.com, mcgrof@kernel.org, dhowells@redhat.com, djwong@kernel.org, hare@suse.de, da.gomez@samsung.com, dchinner@redhat.com, brauner@kernel.org, xiangzao@linux.alibaba.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <066dd2e947ccc1c304b54e847fbe628dccea1d7c.1773370126.git.baolin.wang@linux.alibaba.com> <0890a207-354e-4da1-80c2-67754354a6a6@arm.com> <726ee101-6978-49f6-8f2b-edc7f8d99074@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 9B34FC000B X-Rspamd-Server: rspam08 X-Stat-Signature: zesejoqhafa57gq1ob3ox1geat7njdmk X-HE-Tag: 1773709498-297554 X-HE-Meta: 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 Yu14pXUH /MHkw69YtrYnzl+DOlpCZEn20GJd+SdKY14M2+lDJVn2g7YJgmEMy5mIPZ/Q6ZDym92Zg0/nYgINNb6Iq5ia8TinAzRJMvupYNLWMj+2ksHJ8um3T1OAohnfvppEUyJALoQlM0J4hF4b6iNo2fnvivI+ZWq6beUqfwGW29ITrczla2fxCfh/08+xhN3/USRFhyKifJU0sbm8/PqKolm80VJia1094/MyCRDCBWVkFjOBH/x86KewFqG3edSq5J5teiVU4fkerIXHPWLdRsAVfZZgyznxpuX97CBqHuAhVUEWwMuPfDJxX1XCqqtggkR1eTlt9etF3y1E2gwXnb7UWtOh7DJevACdy4QyptN2rovKwLFAuzKkOSGZtPLkDlYOxtRFK8Gmlah9Zv5A= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/16/26 8:00 PM, Kiryl Shutsemau wrote: > On Fri, Mar 13, 2026 at 01:54:31PM +0800, Baolin Wang wrote: >> >> >> On 3/13/26 1:14 PM, Dev Jain wrote: >>> >>> >>> On 13/03/26 10:41 am, Dev Jain wrote: >>>> >>>> >>>> On 13/03/26 9:15 am, Baolin Wang wrote: >>>>> When running stress-ng on my Arm64 machine with v7.0-rc3 kernel, I encountered >>>>> some very strange crash issues showing up as "Bad page state": >>>>> >>>>> " >>>>> [ 734.496287] BUG: Bad page state in process stress-ng-env pfn:415735fb >>>>> [ 734.496427] page: refcount:0 mapcount:1 mapping:0000000000000000 index:0x4cf316 pfn:0x415735fb >>>>> [ 734.496434] flags: 0x57fffe000000800(owner_2|node=1|zone=2|lastcpupid=0x3ffff) >>>>> [ 734.496439] raw: 057fffe000000800 0000000000000000 dead000000000122 0000000000000000 >>>>> [ 734.496440] raw: 00000000004cf316 0000000000000000 0000000000000000 0000000000000000 >>>>> [ 734.496442] page dumped because: nonzero mapcount >>>>> " >>>>> >>>>> After analyzing this page’s state, it is hard to understand why the mapcount >>>>> is not 0 while the refcount is 0, since this page is not where the issue first >>>>> occurred. By enabling the CONFIG_DEBUG_VM config, I can reproduce the crash as >>>>> well and captured the first warning where the issue appears: >>>>> >>>>> " >>>>> [ 734.469226] page: refcount:33 mapcount:0 mapping:00000000bef2d187 index:0x81a0 pfn:0x415735c0 >>>>> [ 734.469304] head: order:5 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 >>>>> [ 734.469315] memcg:ffff000807a8ec00 >>>>> [ 734.469320] aops:ext4_da_aops ino:100b6f dentry name(?):"stress-ng-mmaptorture-9397-0-2736200540" >>>>> [ 734.469335] flags: 0x57fffe400000069(locked|uptodate|lru|head|node=1|zone=2|lastcpupid=0x3ffff) >>>>> ...... >>>>> [ 734.469364] page dumped because: VM_WARN_ON_FOLIO((_Generic((page + nr_pages - 1), >>>>> const struct page *: (const struct folio *)_compound_head(page + nr_pages - 1), struct page *: >>>>> (struct folio *)_compound_head(page + nr_pages - 1))) != folio) >>>>> [ 734.469390] ------------[ cut here ]------------ >>>>> [ 734.469393] WARNING: ./include/linux/rmap.h:351 at folio_add_file_rmap_ptes+0x3b8/0x468, >>>>> CPU#90: stress-ng-mlock/9430 >>>>> [ 734.469551] folio_add_file_rmap_ptes+0x3b8/0x468 (P) >>>>> [ 734.469555] set_pte_range+0xd8/0x2f8 >>>>> [ 734.469566] filemap_map_folio_range+0x190/0x400 >>>>> [ 734.469579] filemap_map_pages+0x348/0x638 >>>>> [ 734.469583] do_fault_around+0x140/0x198 >>>>> ...... >>>>> [ 734.469640] el0t_64_sync+0x184/0x188 >>>>> " >>>>> >>>>> The code that triggers the warning is: "VM_WARN_ON_FOLIO(page_folio(page + nr_pages - 1) != folio, folio)", >>>>> which indicates that set_pte_range() tried to map beyond the large folio’s >>>>> size. >>>>> >>>>> By adding more debug information, I found that 'nr_pages' had overflowed in >>>>> filemap_map_pages(), causing set_pte_range() to establish mappings for a range >>>>> exceeding the folio size, potentially corrupting fields of pages that do not >>>>> belong to this folio (e.g., page->_mapcount). >>>>> >>>>> After above analysis, I think the possible race is as follows: >>>>> >>>>> CPU 0 CPU 1 >>>>> filemap_map_pages() ext4_setattr() >>>>> //get and lock folio with old inode->i_size >>>>> next_uptodate_folio() >>>>> >>>>> ....... >>>>> //shrink the inode->i_size >>>>> i_size_write(inode, attr->ia_size); >>>>> >>>>> //calculate the end_pgoff with the new inode->i_size >>>>> file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE) - 1; >>>>> end_pgoff = min(end_pgoff, file_end); >>>>> >>>>> ...... >>>>> //nr_pages can be overflowed, cause xas.xa_index > end_pgoff >>>>> end = folio_next_index(folio) - 1; >>>>> nr_pages = min(end, end_pgoff) - xas.xa_index + 1; >>>>> >>>>> ...... >>>>> //map large folio >>>>> filemap_map_folio_range() >>>>> ...... >>>>> //truncate folios >>>>> truncate_pagecache(inode, inode->i_size); >>>>> >>>>> To fix this issue, move the 'end_pgoff' calculation before next_uptodate_folio(), >>>>> so the retrieved folio stays consistent with the file end to avoid 'nr_pages' >>>>> calculation overflow. After this patch, the crash issue is gone. >>>>> >>>>> Fixes: 743a2753a02e ("filemap: cap PTE range to be created to allowed zero fill in folio_map_range()") >>>>> Reported-by: Yuanhe Shu >>>>> Tested-by: Yuanhe Shu >>>>> Signed-off-by: Baolin Wang >>>>> --- >>>>> mm/filemap.c | 6 +++--- >>>>> 1 file changed, 3 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/mm/filemap.c b/mm/filemap.c >>>>> index bc6775084744..923d28e59642 100644 >>>>> --- a/mm/filemap.c >>>>> +++ b/mm/filemap.c >>>>> @@ -3879,14 +3879,14 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, >>>>> unsigned int nr_pages = 0, folio_type; >>>>> unsigned short mmap_miss = 0, mmap_miss_saved; >>>>> + file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE) - 1; >>>>> + end_pgoff = min(end_pgoff, file_end); >>>>> + >>>>> rcu_read_lock(); >>>>> folio = next_uptodate_folio(&xas, mapping, end_pgoff); >>>>> if (!folio) >>>>> goto out; >>>>> - file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE) - 1; >>>>> - end_pgoff = min(end_pgoff, file_end); >>>>> - >>>>> /* >>>>> * Do not allow to map with PMD across i_size to preserve >>>>> * SIGBUS semantics. >>>> >>>> I am wondering whether something similar can happen in the do-while loop >>>> below this code. We can retrieve a folio from next_uptodate_folio, and >>>> then a massive truncate happens and we end up mapping a large folio >>>> into the pagetables beyong i_size, violating SIGBUS semantics. (truncation >>>> may back-off seeing the locked folio/increased refcount in filemap_map_pages) >>> >>> Read the bracket text as - (truncation may fail to unmap this folio seeing >>> it locked or with elevated refcount, therefore the illegal mapping stays >>> permanent) >> >> IMHO, the truncate_pagecache() will call unmap_mapping_range() twice, and >> the folio lock and refcount will not block unmap_mapping_range() to unmap >> the folio's mapping (only hold ptl lock). >> >> So the truncate_pagecache() can still truncate large folios beyond i_size. > > Yeah, we serialize here on the folio lock. It should be safe. > > The fix looks sane to me: > > Acked-by: Kiryl Shutsemau (Meta) Thanks for reviewing.