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 3B59A3E7145; Thu, 24 Sep 2026 07:50:12 +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=1790236214; cv=none; b=Ft4aa8AUGscBSnHmyy3+PeciFwIAXqfa6moFSsrsmV8eAzx2f7xhPimbz/23QDX5dOUlg8nfAnmmqyKK3v5nZqJFIb7g+Hsar+/p5nTGag2L4UOTbFslLFMr1n4jOScEzcENxwjUkLNI7ZPJZg8RRjpbHQo8ZwanHVPVh8vpbhc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790236214; c=relaxed/simple; bh=Qj0te7eGJQSqezg4WUh94TJNtvGrDCfxRYklUhsZl7s=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=W3gxGwOfV/Zva70H/a5/XGMFrChlClBQPvqCVjqx/1xJWzpZx+FSAAmsFCcxO5U4h0UXfpbDq34jdxnCMFs7UWvlUx4pdY9irRe9No6SC+dSxaytmnYTn46Jw+ZRNgT7drKrmS5aHFcE7Zfha7eUfAIBILSQhD2+B1u1YgKCBG0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eRT+7H9A; 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="eRT+7H9A" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B5D691F000FF; Thu, 24 Sep 2026 07:50:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790236212; bh=XDvywVc6Ep1SuVeW2SGy85kW0rD7YUN5EGSklkhHzQk=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=eRT+7H9ABPwFjh7BVERhP8cozvQ4MQhStKNB7IRvgfIVy1HpxDFA1S9CLNaBl5pzI KbWjS+JLXuC1wfFOu3O1kKNSLzYoFlGe7Tv2kGJimLChc4ZoVJCdySlQ6e/Tz0sL1D U0iYGLcnxGjb2dU5iqN0HCoSkRnXP9Xme2baHRJ40E4KIM8t0wkAmMfPUSppRNQrim DTNpz+zdjksrk7NtzRiTQlySjLsTl2p+yx+bYXTEnPJmuk8zk0/jV46rM7nWCxR/1h T2pphZq6jbBIsqIE5qVV+FHA7Q1fgJbsv1XCiH44gQdnf98X4nCMENM2ur68i1YPoB mW+MzuRrfmFrA== Message-ID: <08bbb615-a054-472c-9873-787cc0f7a4d7@kernel.org> Date: Thu, 24 Sep 2026 09:50:02 +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: [syzbot] [mm?] [ext4?] WARNING in __folio_set_anon From: "David Hildenbrand (Arm)" To: Lance Yang , ljs@kernel.org, akpm@linux-foundation.org Cc: harry@kernel.org, jannh@google.com, liam@infradead.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, riel@surriel.com, syzkaller-bugs@googlegroups.com, vbabka@kernel.org, syzbot+c181d3198e98f8aef8b9@syzkaller.appspotmail.com References: <6ab4ae75.80e1c6cc.1e8e5f.000d.GAE@google.com> <20260924065458.49698-1-lance.yang@linux.dev> <0a0a07f8-8ac9-4d75-b4c6-c403865f0be9@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/24/26 09:43, David Hildenbrand (Arm) wrote: > On 9/24/26 08:54, Lance Yang wrote: >> >> On Wed, Sep 23, 2026 at 10:00:37PM -0700, syzbot wrote: >>> Hello, >>> >>> syzbot found the following issue on: >>> >>> HEAD commit: 38872197cae2 Merge branch 'for-next/fixes' into for-kernelci >>> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci >>> console output: https://syzkaller.appspot.com/x/log.txt?x=17a44d25580000 >>> kernel config: https://syzkaller.appspot.com/x/.config?x=56ed23170c168d4c >>> dashboard link: https://syzkaller.appspot.com/bug?extid=c181d3198e98f8aef8b9 >>> compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 >>> userspace arch: arm64 >>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16a36515580000 >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16dcf4c9580000 >> >> Looking at the repro, emm ... the repro maps an O_RDONLY /dev/zero fd with > > Does this trigger upstream or only after Lorenzo's rework (not upstream yet IIRC) > > 46827ac1ab221 mm/vma: make MAP_PRIVATE-mapped /dev/zero mappings truly anonymous > db7438ea23180 mm/vma: only permit MAP_PRIVATE /dev/zero to be mapped anonymous > 54e8e096ea86b mm: implement file_is_dev_zero() to uniquely identify /dev/zero > fb24843cfd9eb mm: move drivers/char/mem.c to mm/char-mem.c > > I assume it triggers upstream. Does it also trigger with lorenzo's changes? > >> MAP_SHARED | PROT_READ. do_mmap() clears VM_SHARED and VM_MAYWRITE, so > > Clearing VM_MAYWRITE for a private mapping is odd. Can you point me at the code > that clears both things? > > I assume we still have the file pointer, and as the file is read-only we remove > VM_MAYWRITE. But why are we removing MAP_SHARED? (where?) Looking at the code, it's the if (!(file->f_mode & FMODE_WRITE)) vma_flags_clear(&vma_flags, VMA_MAYWRITE_BIT, VMA_SHARED_BIT); So we end up with VMA_MAYSHARE_BIT but without VMA_MAYWRITE_BIT and without VMA_SHARED_BIT. So it's by definition not a COW mapping. But it's marked anonymous and confuses the system :) -- Cheers, David