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b=oaUxo5t9YbeDFk9IsF47EFi/fCesBtSnhJioplSOIuwq7qbfjCo+IAL6GBfJdoq3g kQIqECieYiHk7aOvyXfBy4Dyb9sgaH0nFDDZF6SkwG7oNEgNTioXBFqSgRyPEpsQEH c7mkrVNSxAcL4RLrAOaakS14laEON0zW8aN4zFRjSwzoCAGUXI3dUyNw03NzZ8HXmy XqIhmh+tkMyj0r+Y4Paatxt0c64ZYHfJ8ZH+M9WXOTElvHUEi/8Knpt0Nk38JKH5yR hPWGNXnFYMavP6i+MC3HH6i10TrpCzPd7UeWuHu1+O1XBxWkeCjcmehPeb1wiSKC9k 127vQxEQma1uA== Message-ID: <9d968181-95a9-477e-9aa0-763117e4d1a0@kernel.org> Date: Tue, 17 Mar 2026 10:37:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: filemap: fix nr_pages calculation overflow in filemap_map_pages() To: Baolin Wang , 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: <1cf1ac59018fc647a87b0dad605d4056a71c14e4.1773739704.git.baolin.wang@linux.alibaba.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 74D6EA0011 X-Stat-Signature: j4xpjpy3mrmdi4omhbhehun4y5a3f9pf X-Rspam-User: X-HE-Tag: 1773740229-45644 X-HE-Meta: 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 6FdUR6vv BHUDKBdWv8TsmjmTZX5rSgwVk8iFfGToYZ/u5k2Zm9IEn9BAVxQRqYFxBzrKQKb1FKOSNn5yvOYyg3erRM1G6jN39ot7SN92dFvtQ2h3TJbKRT1dBnlsbjPVp3PqLlM8jdqEVwib71IqFkPF2sT8Vkj4onpDZ8EHySztEhn0J3Ll5wTxLxLkDakDngftUdpdSjMbjnu5dffUHPdcip+HsiIG9zUi4rd5I17k6J8GlLcnjqyzse5KIT7bHWzDwKCbRPEtbNHz6GNa1y6jfgvrSVnr/QHsC1V3S2lON/BRg+SKuJlbVOnuR2NS1gXly8Kjv9SbKv77KH7G4NhnaaD93AqJ2ZqimC4uPVq91 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/17/26 10:29, 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. > Thanks! Acked-by: David Hildenbrand (Arm) -- Cheers, David