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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2D9061C0004 X-Stat-Signature: 3yo1i1mqthcpujz9degbn4ioobiejuc5 X-Rspam-User: X-HE-Tag: 1773378714-659126 X-HE-Meta: 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 xip4629y 75pfIPYJAn4Mh2tSraaMkK0bOkW5oIML/oo0tDY3uI4ylLsZJ6p690ilH/KnBdtWcU5FTqFRqZ0UJlT7TL0u5cXewhQtlbwU4yZFfcpuoEF3a49WW0FLG2g1CJE57cUO5X+0l01H7r456N3p/ldoqAvYx7hK0eb8xkz/T6a63IuG40i9+/kBrqcE8R3eqsvuaCBBMlrL10VN9XBJuOk5uXtwVgxYKcmF/eMckGuILJUU0GsM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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)