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[2003:cb:c745:2000:5e9f:9789:2c3b:8b3d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43d1fe065b0sm15827845e9.14.2025.03.14.05.17.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Mar 2025 05:17:06 -0700 (PDT) Message-ID: <95a15856-5c47-4040-9291-5b972786efeb@redhat.com> Date: Fri, 14 Mar 2025 13:17:05 +0100 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 v3 08/10] selftests/mm: Skip gup_longerm tests on weird filesystems From: David Hildenbrand To: Brendan Jackman Cc: Lorenzo Stoakes , Andrew Morton , Shuah Khan , Dev Jain , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250228-mm-selftests-v3-0-958e3b6f0203@google.com> <20250228-mm-selftests-v3-8-958e3b6f0203@google.com> <08023d47-dcf4-4efb-bf13-5aef3c6dca14@redhat.com> <16023193-6cb4-46d1-91c4-43342e7e6d30@redhat.com> <41923b80-55f4-44b6-bc59-60327e5308f4@redhat.com> <15cc0c1d-2b02-41de-bf48-3c57cee97c53@redhat.com> Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <15cc0c1d-2b02-41de-bf48-3c57cee97c53@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 14.03.25 13:10, David Hildenbrand wrote: > On 12.03.25 09:34, Brendan Jackman wrote: >> On Tue, Mar 11, 2025 at 08:53:02PM +0100, David Hildenbrand wrote: >>>> 2. 9pfs seems to pass the f_type through from the host. So you can't >>>> detect it this way anyway. >>>> >>>> [3. I guess overlayfs & friends would also be an issue here although >>>> that doesn't affect my usecase.] >>>> >>>> Anyway, I think we would have to scrape /proc/mounts to do this :( >>>> >>> >>> The question I am asking myself: is this a 9pfs design bug or is it a 9pfs >>> hypervisor bug. Because we shouldn't try too hard to work around hypervisor >>> bugs. >>> >>> Which 9pfs implementation are you using in the hypervisor? >> >> I'm using QEMU via virtme-ng. IIUC virtme-ng knows how to use viortfs >> for the rootfs, but for individually-mounted directories with >> --rwdir/--rodir it uses 9pfs unconditionally. > > Ah okay, that makes sense. > >> >> Even if it's a bug in QEMU, I think it is worth working around this >> one way or another. QEMU by far the most practical way to run these >> tests, and virtme-ng is probably the most popular/practical way to do >> that. > > I'm afraid yes. Although allocating temp files form 9pfs is rather ... > weird. :) One would assume that /tmp is usually backed by tmpfs. But > well, a disto can do what it wants. > >> I think even if we are confident it's just a bunch of broken >> code that isn't even in Linux, it's pragmatic to spend a certain >> amount of energy on having green tests there. >> > > Yeah, we're trying ... > >> (Also, this f_type thing might be totally intentional specified >> filesystem behaviour, I don't know). > > I assume it's broken in various ways to mimic that you are a file system > which you are not. > > Your approach is likely the easiest approach to deal with this 9pfs crap. > > Can you document in the code+description better what we learned, and why > we cannot even trust f_type with crappy 9pfs? Staring a bit at that code, it's mostly 9p specific I think. t14s: ~/git/linux s390x-file-thp2 $ git grep "= NFS_SUPER_MAGIC" fs/nfs/super.c: buf->f_type = NFS_SUPER_MAGIC; fs/nfs/super.c: sb->s_magic = NFS_SUPER_MAGIC; t14s: ~/git/linux s390x-file-thp2 $ git grep "= V9FS_MAGIC" fs/9p/vfs_super.c: sb->s_magic = V9FS_MAGIC; $ git grep "f_type" | grep 9p fs/9p/vfs_super.c: buf->f_type = rs.type; -- Cheers, David / dhildenb