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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 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 X-Rspamd-Queue-Id: 9393340006 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: uicahkhdqh5e8713tikb4qeppaudkx8k X-HE-Tag: 1790236213-880269 X-HE-Meta: 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 NoTP9ahe 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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