From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 42707201113; Fri, 13 Mar 2026 05:11:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773378716; cv=none; b=A+XoYJBghqrErVYOswygif5PPlvBhonWi1uBeuadACBhski3GfbbeeTuBfzV3BYfAq9MOb5qjFesE/e16zZt3SAJpkFoTtYxPC2O9tM5Klll+dViomJuUWDi3kn3Bm6mX6l820ZgMJZnghCBNGm16tpgwkA0BMSHocKfq9rFKaQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773378716; c=relaxed/simple; bh=q+lQQcrFgbLzIQgm9vnEFHsfhIBoC6di6u5RmsM4Vds=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GBJIxxhNusFdcm9QoK6rN4eHr4jEJjQCOBWcDgya/8Lu8kD3+GHf+Kx3xK+niC1u7uEbJk/ywvutiVPg3/xHcBmN0S4g9Up/r9hUwap+Ed/omnu8DJfMKmrrWFHaMznmqE4t3r7e83reUo1NnuG4yoe7gplhxOyxS8nA34jokq0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EAE36165C; Thu, 12 Mar 2026 22:11:46 -0700 (PDT) Received: from [10.164.19.59] (unknown [10.164.19.59]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9B3853F694; Thu, 12 Mar 2026 22:11:48 -0700 (PDT) Message-ID: <0890a207-354e-4da1-80c2-67754354a6a6@arm.com> Date: Fri, 13 Mar 2026 10:41:45 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: 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> Content-Language: en-US From: Dev Jain In-Reply-To: <066dd2e947ccc1c304b54e847fbe628dccea1d7c.1773370126.git.baolin.wang@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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)