From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com [115.124.30.132]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2BB9C282F34; Fri, 13 Mar 2026 05:54:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.132 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773381280; cv=none; b=rqRqBwcZ7rgZJiPRhMuM255wvSYWBGGScjDyNSrvQ4OZ2rI3bMiXLXlZJBxDmh3x7ugpCWFt27oN0a5IXrU1Df5NTS0oWcg8E2OINvpfSB0XhD+1KIqaxXILMfEggxpzJHkeWn5I0G/57sxPrATTtQyQIyT0mTKRj8KTbwEXnz0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773381280; c=relaxed/simple; bh=O2HXLpaxWlFj6yPv/IIIUKi+5QMsSa1obpT0DtqTmjI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=rnMcGoLRobetzcNaSW0ooESd8gmEJvOSQ3+X7RmYBVaP4qosHeIstYFaOXB/lCBJLS0Ca2GIM2txNmOYPEIPwKGXummcehW54N01RQHf32MG+PvK8cg7mA12unh4OaLcL/lfTrXba4fuO/Odv1fE5ow/fihz9/GZsvzO4DD0tQ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=g/3j/+pU; arc=none smtp.client-ip=115.124.30.132 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="g/3j/+pU" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1773381274; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=oczUtkjqR/GKMWS4UhWTZ6MNDRiOWQJyorrZCEgN1Dg=; b=g/3j/+pU5uQBscEcj0AHCQQt64eFGPksA756c1aEXtVk8CxslDf31hSFHzhdrH2HhqoIafxLZK0kXfaeaU+K7HKiEy30nFyYpc+Ve16cChXMKxlSy2rMe71iTBXZTp+KUhTGsOKExkHWgbxtUTxcE5pyBUopCb2jR6hRUKielLk= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R841e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045098064;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=18;SR=0;TI=SMTPD_---0X-rAXAR_1773381271; Received: from 30.74.144.121(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X-rAXAR_1773381271 cluster:ay36) by smtp.aliyun-inc.com; Fri, 13 Mar 2026 13:54:32 +0800 Message-ID: <726ee101-6978-49f6-8f2b-edc7f8d99074@linux.alibaba.com> Date: Fri, 13 Mar 2026 13:54:31 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: filemap: fix nr_pages calculation overflow in filemap_map_pages() To: Dev Jain , akpm@linux-foundation.org, willy@infradead.org Cc: david@kernel.org, lorenzo.stoakes@oracle.com, kas@kernel.org, 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> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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.