From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8A8B647D451 for ; Mon, 12 Oct 2026 10:23:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791800606; cv=none; b=RxKOhLjDVGQpP4QteEDcjjKFfPfnYDmHcy58l/A3godnMxiZov6fmjD6fOfZBzOcN0KDooIERHm8ReVUCPDaZyB31EYZPb67YVM1MzZCH/3fP3Sw5siRjkcoCP3sSeTDlcBB2PAdZNLfdB+aHFFLNsgxTYuS8kvGFlGJ0fMpkmE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791800606; c=relaxed/simple; bh=B9qbRywECfyJEffntEQqfPP1MOzHae408HOr3lKU468=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=MJPrfAngNoJtp+mVVPn6oj76/MP9vJw7MxCi9S8NeGMDv8Ss+tG69C7/rQte+MRGW9Eos9JwjQCcAcm8+pHqCpLfrCGqDNKCrglDtCxaC5tpfN9MI+JB6N1MMPRV9+t9GL8rwP0lmPqxJR859SbLu+KqknZNmPt9L+6PY+iov54= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NKW0ZQ5y; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NKW0ZQ5y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 99F191F0089F; Mon, 12 Oct 2026 10:23:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791800592; bh=3z5VmndhUnm6M1SGNXwdEBCW+kXS3dFLbMdOYvBRK1Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=NKW0ZQ5y5yu1KDZuEBDuq5AHnO+AwF0hXY5f0rqVjf7do3lWR/THYgKzQho7s0jeK MBrHdg5cRFWD2E9foRCc7WCGn85Zp/lHvT6ZvNroYolUnwgskLYqEtD5BxQ+vHYZX9 SHpdfxBv70t9HBT0b8smDkNIak8/XmUgNYsIoh4E8MaLt5KDGSRGh/ghhGHW+GsY/A wSX4XJkuCVFay9yP7JJ8W0QxDvqWHNcUUzSIojEMBFShyoJolY4cI3Pio4I2lXDfxG Ey/w3BlhSghn051P12y8YUkfvHW4Et5Xv2JzpBjaQyTH5zs/197ZWd0S+UBDCrfIMl ythKfl/uJSmlw== Message-ID: <8245424a-f068-4be5-9e58-713cbff1f8ae@kernel.org> Date: Mon, 12 Oct 2026 12:23:07 +0200 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: [PATCH v2] mm: memory: fix truncation removing mapped folios To: Baolin Wang , akpm@linux-foundation.org Cc: ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, qi.zheng@linux.dev, jack@suse.cz, pfalcato@suse.de, ayushr@modal.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <542c97482eae84f86704bcee56482633d1b32321.1791616645.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: 7bit On 10/10/26 09:22, Baolin Wang wrote: > Ayush reported an issue that shmem/tmpfs folios are still mapped when > truncating them on production: > " > BUG: Bad page cache in process ... pfn:... > page dumped because: still mapped when deleted > " > > I reproduced the issue with Ayush's reproducer [1] with the latest mm-unstable > branch, and I got the following crash info. From the dump message, we can > see that truncate_inode_folio() is really trying to remove mapped folios, > which is incorrect. > > " > [ 189.171977] page: refcount:3 mapcount:1 mapping:00000000fe168ee1 > index:0x3880 pfn:0x191647 > [ 189.171995] memcg:ffff0000cc073d40 > [ 189.171997] aops:shmem_aops ino:3c01 dentry name(?):"memfd:runsc-memory" > [ 189.172006] flags: 0x17fffef0002022d(locked|referenced|uptodate|lru| > workingset|swapbacked|node=0|zone=2|lastcpupid=0x3ffff) > ....... > [ 189.172017] page dumped because: VM_BUG_ON_FOLIO(folio_mapped(folio)) > [ 189.172026] ------------[ cut here ]------------ > [ 189.172027] kernel BUG at mm/filemap.c:155! > [ 189.172057] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP > ....... > [ 189.177721] CPU: 3 UID: 0 PID: 5521 Comm: repro Kdump: loaded Tainted: > 7.3.0-rc4+ #277 PREEMPT(lazy) > ....... > [ 189.183986] Call trace: > [ 189.184124] filemap_unaccount_folio+0xf0/0x1e8 (P) > [ 189.184391] __filemap_remove_folio+0x34/0x160 > [ 189.184633] filemap_remove_folio+0x4c/0xb0 > [ 189.184859] truncate_inode_folio+0x34/0x58 > [ 189.185087] shmem_undo_range+0x220/0x658 > [ 189.185308] shmem_fallocate+0x2f0/0x470 > [ 189.185527] vfs_fallocate+0x128/0x328 > ...... > [ 189.187078] el0t_64_sync+0x184/0x188 > " > > After analysis, I believe the race exists between truncation and MADV_DONTNEED, > and shmem's ->map_pages() merely makes the issue easier to reproduce. Since > MADV_DONTNEED synchronously releases the pagetable page before calling > tlb_flush_rmaps(), this could cause another thread's truncation to skip > zap_pte_range() (due to pmd is none) but still observe the folio's mapcount > as non-zero. A possible race scenario is as follows: > > CPU 0 CPU 1 > shmem_fallocate madvise_dontneed_single_vma > unmap_mapping_range ....... > ...... > (filemap_map_pages() remap folios) > zap_pte_range > truncate_inode_folio zap_empty_pte_table(pmd clear) > unmap_mapping_folio > ...... > zap_pmd_range (saw pmd none, skip) > > filemap_remove_folio > BUG_ON(folio_mapped) That reminds me of sync_with_folio_pmd_zap() usage in page_vma_mapped_walk(). Isn't that the better approach? -- Cheers, David