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b=bqxwsTyh2/WRTSkMtCg+asur/mX9EB67RTFniApswkXFVqM1YMWzO3B69vQoz6X7U qjsArsAkHI5kAoN3MXpgws9EoNaVIGOjR1YEmkJ0BIhqd5HTojwInULoKILQT0/gBp OcFdEn+A3oSWWWnL66Cyc3CEUvGvavlibj9GAPBE5nItnoJX6o+c/wij2XAW9XiVcY 6torzdTAWqR3XmCXqye9YPWPWbx0kgpSvRxcBpu0oFsZBH4bU+NhhmcpNeqAHYQpZW YepEXaenR8/b17VR93u33Bvf5qVS5kbiXxiL0cJcubE1DJ6JXIlru7X7GZlYP5ZsTZ EQgNWvzwGx/bQ== Message-ID: <82019011-023c-4bce-a524-6eab119f0a4a@kernel.org> Date: Tue, 17 Mar 2026 21:49:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: filemap: fix nr_pages calculation overflow in filemap_map_pages() From: "David Hildenbrand (Arm)" 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> <9d968181-95a9-477e-9aa0-763117e4d1a0@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4651518000B X-Stat-Signature: mmzw1m59ewutuyzuek8579ranxgaqba9 X-Rspam-User: X-HE-Tag: 1773780585-353361 X-HE-Meta: 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 7CHVGmyZ op595BJicSfNnjP2N7ckHSVHu9GpaDMYQRoQNEjAZvvLtScIUEk5Bc0xzZemjtRn+CeYqk5xB9ByxS9HhOG4O21/TO6o1r21oBe8TLmHK5r8Z6lIWzkdDXZYgr9e/hqT6mlyb+ePPcMQF0ARbDumzR16j7EsqoMVlHOajtgLuTUJ+Dd9VyIv+D1KbeBJm9nzyH0uy1wsR56WRnjgMqdCDa2hxsPoZCI+DY85Ep12kvi2nhcTXNlAuEftSrS7cXCZao8Di4OZbd9Fie/EiHBQ6Sac2uMGlRd846u0NIO2juI3Y/dQqNcd/AwtYJbzJr4DnvB0O/egvkfDwpwCBcOEkHFUA6rb0h3E9JwpiDuvZXqjGYp2oKbrgXsjq7MxhaJNaCDmEQbWm2Zg0cTWRFxO/pEKkKFKLHCiXk7IVBtIcyaPq1+V6vcDLJ1Hp/Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/17/26 10:37, David Hildenbrand (Arm) wrote: > 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) > I just skimmed over the AI review: https://sashiko.dev/#/patchset/1cf1ac59018fc647a87b0dad605d4056a71c14e4.1773739704.git.baolin.wang%40linux.alibaba.com And I'm not sure if it has a point, in particular whether i_size_read(mapping->host) could return 0 and underflow file_end. I'd assume, in that case (truncation succeeded), also the next_uptodate_folio() would fail. But it's tricky :) -- Cheers, David