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b=oDjPz+SZbJH+CX/UgG+Y8rgCIz/PyCjUzfp6dusJq1X2Hnk5ei6U1Z4Ij3fHTYi4m CjgiCnA+XPR0hp3sGEa5UWoADfs9n2BBjTwu8g6RgHp5hTQO8BoFPhZdXIjHsw0LNr xtRsyYPrij1pBCmo9KUbT3C8HqYNKmCijkk23B4MiwrUp/e7DiFEFYTWWzOujMJ5XB FusXnuDNop4d3wqSVDJiu+YY6zhmPFFRKVUggmW0Dtxqdr2jYrmFpjytJWXfhkck/q Gluaa0k6qwbpjG2xDygJR54Zob1cHwuAlgL3j1YHSXWybzPSHV3Ezi2VPIW8O9Hz9n KADxaiZTyooYw== Message-ID: Date: Mon, 16 Mar 2026 15:06:26 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 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: <066dd2e947ccc1c304b54e847fbe628dccea1d7c.1773370126.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-Stat-Signature: 3hy37rmspsqq9bxxfrh4npyq4rs5yxf9 X-Rspam-User: X-Rspamd-Queue-Id: A6D8C40010 X-Rspamd-Server: rspam12 X-HE-Tag: 1773669993-159438 X-HE-Meta: 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 42uNeXaK Anq050vFlEAFqLA11ICHhznw5N1WjgWOLIi0DDfsZthD+AybjYcOgfIEku7DbllXw6PEfJZ6UVL+2Dwf3Ae9/dA4URP1/bD2GgJZB6vcH1fRe06v75wDpCwUwKzxRUZF4TX+5D4ztXaK4GvngTyUgjf3y88XoEPCjorLT4VVtLlL5dlxY/QLUczDu0jDcFHmC/aulcdlkI3AQ4TL5SiWmlAwA3R4wLZClQuUk747UldTtSQiUhir3OvqTH4BRzHMySFL5eyD4dSIybAWXCCd9SEzQc+TZzlMAmPrlTz6jjtG16TsSNEd0q296llNI0trbhDOvK77vjAiNdv4DljiXmT57ZOBQTvEQBWvxRPVyYD3UQiVrS0jW3QcJJpNfLIeO+HYgVEkdR3TfdGsuFsxhFLikourIQXOpZG9srNtNbhXDV3k41efJOUvxDRibU6x0K76xfI6aFAeYKho= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/13/26 04:45, 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. We had a bunch of similar reports throughout the last year from syzbot, but always without a reproducer. In particular this here: https://syzkaller.appspot.com/bug?extid=c0673e1f1f054fac28c2 via https://lore.kernel.org/all/6758f0cc.050a0220.17f54a.0001.GAE@google.com/ Could that be the same root cause? > > 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). Sounds quite bad. > > 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()") This certainly sounds like stable material :) > 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. LGTM. I do wonder if we want to add a comment above the file_end, stating that this really must happen before the next_uptodate_folio() to handle concurrent truncation. -- Cheers, David