From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-119.freemail.mail.aliyun.com (out30-119.freemail.mail.aliyun.com [115.124.30.119]) (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 1130E1D9A66; Tue, 17 Mar 2026 01:05:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.119 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773709505; cv=none; b=IEyelhzSSChsfCDwlb0abHvUF1Gz89afAR7MB+HXJ0SCLHreZZ80C8qET2ThkaEAWqG7rFyg508dJeUI/+zUAH1Km+EZngIBpHIk9JtM3rbv/GVl6nn0zkFLKfVurdNLHsjLAmQdM7YTgG9xePAC6F+dQGUUq99yriVG9We5Uu4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773709505; c=relaxed/simple; bh=R56SDBhL7kwyjUzC//zj7+thmOmwth4d1PVEz5bPJV8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=q6HOGy1lhuIXcurCYC3t4+FyYRw4RKb9KewUtyzLi/e5eqvXS0GWCydkqiYmE3pCTgrwBuOBDOQa7HybUjyNuoHblJ6WkV2CmuhH8wW/qjvR+HmtL1Knz1CvPeZF3WGdhw+vNPOmJDzZ9QGPzqIOKa31Z3rG6oZPABGZ6GKweFM= 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=S4u0coRT; arc=none smtp.client-ip=115.124.30.119 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="S4u0coRT" 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 Precedence: bulk X-Mailing-List: linux-fsdevel@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: 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 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.