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b=PgR1b/KMZs/3YFaqWxPqpgU13UCHkGVjn5fdwOWwTCAeWAHSXeaAH9eJt3voR8IU1rKgRCUzvIwwzwJls3mcTBjT5uR2L6Zz2rjFIKTyCoZUGKMA+VJeF7W03soNPVZkpr6wQfquKFPmax5GhLHTb+5iz02TeaoQi7g1zwN3Kkw= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R671e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam011083073210;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=18;SR=0;TI=SMTPD_---0X.Abv.D_1773739802; Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X.Abv.D_1773739802 cluster:ay36) by smtp.aliyun-inc.com; Tue, 17 Mar 2026 17:30:02 +0800 From: Baolin Wang To: 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, baolin.wang@linux.alibaba.com, xiangzao@linux.alibaba.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm: filemap: fix nr_pages calculation overflow in filemap_map_pages() Date: Tue, 17 Mar 2026 17:29:55 +0800 Message-ID: <1cf1ac59018fc647a87b0dad605d4056a71c14e4.1773739704.git.baolin.wang@linux.alibaba.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 32D63120004 X-Stat-Signature: pkucapj6kdezto3cgapx1ikxcqi3e1je X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1773739806-544117 X-HE-Meta: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 Acked-by: Kiryl Shutsemau (Meta) Cc: Signed-off-by: Baolin Wang --- Changes from RFC: - Add acked tag from Kiryl. Thanks. - Add some comments and CC stable, per David. --- mm/filemap.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index bc6775084744..598890871635 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3879,14 +3879,19 @@ 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; + /* + * Recalculate end_pgoff based on file_end before calling + * next_uptodate_folio() to avoid races with concurrent + * truncation. + */ + 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. -- 2.47.3