From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110]) (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 72E052BFC7B; Tue, 17 Mar 2026 01:16:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.110 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773710188; cv=none; b=sBI3xC/WbXKqIz/7F83rptmRlyckDw1iB5YdViHV1Y3cq/8qlYZp8+TbMO3eeyRrouuLb0K0t9hs/ZUYgbi7HIZwMqAHOoMTOUHMo3bRqlh0XMidfx8pXp7pmFWELmZLEcKJTn16wemJp8OguSsY2nBQI/lCss1vYpG2uuZfWW4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773710188; c=relaxed/simple; bh=iOFU++lxCSWeAaCne3/I2t5mDb87NgTsD2LIqNTbqKY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jEmU7PIdgWBzvBzu0nO3TPKQzociP/NTY0/chkeNTL8QFzqv0oZYQ3WcHeSrjKPWPyjrFgwMgcd2Fo7ivnbhjGxvt1JHxs3jicdadjUTa47pwbVBaNETrUrACtZZ7hwejlUJ9SCgaQqxkqnqnZP9u46nsP00fJr0QcGVW2mpEBg= 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=DStCJ4x0; arc=none smtp.client-ip=115.124.30.110 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="DStCJ4x0" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1773710182; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=zEFreDFoNLZcIvqChYf7kDks1gVkZBJntws5vYQjBJk=; b=DStCJ4x0FDn52on32XijWHbZtTJlB7Om1kx0Fq7M8gWoYB7N8PSlo/4ImQPNzJgHC3x6Q8PeDc4LEW9XXRvCvh/biU34EQzSgB+yqnVu4PCxpf/8SA625FaMbx/IccaEkSYoeHsao7KCPTFcof0iWBfMBZY2h+6Vvzw2j0UUIxI= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R251e4;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=17;SR=0;TI=SMTPD_---0X.94iKz_1773710180; Received: from 30.221.57.233(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X.94iKz_1773710180 cluster:ay36) by smtp.aliyun-inc.com; Tue, 17 Mar 2026 09:16:21 +0800 Message-ID: <23953888-15d6-4cef-af8c-be15ed6d6e20@linux.alibaba.com> Date: Tue, 17 Mar 2026 09:16:20 +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: "David Hildenbrand (Arm)" , akpm@linux-foundation.org, willy@infradead.org Cc: 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> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 3/16/26 10:06 PM, David Hildenbrand (Arm) wrote: > On 3/13/26 04:45, 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. > > We had a bunch of similar reports throughout the last year from syzbot, > but always without a reproducer. I can reproduce it by running stress-ng for a few hours on my 128‑core machine, but I can’t reproduce it on smaller machines (e.g., 32‑core systems). It seems we need sufficient concurrency to trigger this race. > In particular this here: > > https://syzkaller.appspot.com/bug?extid=c0673e1f1f054fac28c2 > > via > > https://lore.kernel.org/all/6758f0cc.050a0220.17f54a.0001.GAE@google.com/ > > Could that be the same root cause? It appears so. Its warning stack calltrace matches what I reproduced. >> 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). > > Sounds quite bad. > >> >> 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()") > > This certainly sounds like stable material :) Yes, will cc stable. >> 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. > > > LGTM. I do wonder if we want to add a comment above the file_end, > stating that this really must happen before the next_uptodate_folio() > to handle concurrent truncation. Ack. How about adding the following comments? " Recalculate end_pgoff based on file_end before calling next_uptodate_folio() to avoid races with concurrent truncation. "