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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 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 X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 78C931C000D X-Stat-Signature: 1kki1958kr49krpaa3nmb3gw9ajxcdhx X-Rspam-User: X-HE-Tag: 1773381276-319453 X-HE-Meta: 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 X3+pnlpx eSQ5iThqq3kBI90i3IGoXwGmz14X847sVgf/wLSKO6V9B2vBkncuHSyzUz7caC2N7AIW4OoGx14pE2IqWemR/svmBZ99rUIwuAl1amK5satgEhlD59KyTGdSsCOIrT7cyGNmB/fDhOhI3ppMGmGJv4dI4t6OmrOCqhLLiR8wXyvwUQeY+HNTkgYCjNVcgeWNuqqW6aDmLGFQ7WpjBtcnnPDqZv0xoKsqHnIvNFSj7QFOamiTG2cHB9M83gXGBHmfDNe69THSOgcTV3N6ICanDiF/BomT7JkImw9cV4HjRkxUbyzGgUiWNjgKYyLbzIMJK6ehtK0uCq88UizwgII0ss7os/wJT6C6Sm018M6Dz82i3KfOst2Ylb8PvOg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.