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(p200300d82f199c0005687df700e1293d.dip0.t-ipconnect.de. [2003:d8:2f19:9c00:568:7df7:e1:293d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45213709729sm16879615e9.19.2025.06.06.02.01.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Jun 2025 02:01:19 -0700 (PDT) Message-ID: Date: Fri, 6 Jun 2025 11:01:18 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm/gup: remove (VM_)BUG_ONs To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Jason Gunthorpe , John Hubbard , Peter Xu References: <20250604140544.688711-1-david@redhat.com> <1a65d0e6-6088-4a15-9c19-537203fe655c@redhat.com> From: David Hildenbrand 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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: -Lnd39vDqEu0evOGHppNv6Adfz2DyGqp4yv7XCmuJwk_1749200481 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: ji7857op1ghx35eyoif1693rfu8inqw7 X-Rspamd-Queue-Id: 827E5A0022 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1749200483-499061 X-HE-Meta: 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 e1CdsExi /DfMEuACSC9a+ZVR+RPX5yHmLF/0ykjlFOHotOfxeXQV8T+IZnKrsU+cO8RaPOPeRajGg3tC+cBS5g8SR1eqceIjGig/0IScxCPkAnNymliRjISI4ne88vA98OPr1iZtnR4crQNP68TmAhvyoGwLBDrqZp5NY2d912dlHHY7S+VlzWvGbkhSW2lHfQq1T7vBIGD0DwXVpyQ22JwwmpgXv5bWvoTEB0+JxrtdY43zpmqcYh2Hxf26CL+SzOShkzLxXZgMOykBNbKD7tgXpxmCyRY2acsdwBNbQ2tektZ54D0L1ObEZtOV59k7VRbj+wpA0M14c/Yiov/y7JZNcaT/LxT5f0/jbLVOdE7i+olwRXZJ1GQPTpsX2kpULZVJipJvm6oAeyGgPxllD4O41QCzJq9sLmCQ3ia0dO9Z8KA1VpMvYvgvHum6HzMTMvTd39S0zS4VgPgi8T1q9rVE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 06.06.25 10:31, Michal Hocko wrote: > On Fri 06-06-25 10:10:14, David Hildenbrand wrote: >> On 05.06.25 09:10, Michal Hocko wrote: >>> On Wed 04-06-25 16:05:44, David Hildenbrand wrote: >>>> Especially once we hit one of the assertions in >>>> sanity_check_pinned_pages(), observing follow-up assertions failing >>>> in other code can give good clues about what went wrong, so use >>>> VM_WARN_ON_ONCE instead. >>>> >>>> While at it, let's just convert all VM_BUG_ON to VM_WARN_ON_ONCE as >>>> well. Add one comment for the pfn_valid() check. >>>> >>>> We have to introduce VM_WARN_ON_ONCE_VMA() to make that fly. >>>> >>>> Drop the BUG_ON after mmap_read_lock_killable(), if that ever returns >>>> something > 0 we're in bigger trouble. Convert the other BUG_ON's into >>>> VM_WARN_ON_ONCE as well, they are in a similar domain "should never >>>> happen", but more reasonable to check for during early testing. >>> >>> The patch itself makes sense and I think it is good time to revisit old >>> discussion [1] and finally drop VM_BUG_ON altogether and replace it by >>> VM_WARN_ON which could be still a useful debugging aid. >> >> Yes. I think we should check all cases if they are really relevant (and are >> clear), and also handle BUG_ON on the way. > > There are more than 600 VM_BUG_ON instances.I am not sure it is > feasible to review single one of them. I'm sure we would be done if we would have started back when Dave R. sent his patch ... :) It's not that many files, and many checks in a file are often of a similar kind. Like many "folio_test_locked" checks. > Turning them into VM_WARN_ON > should be reasonably safe as they are not enabled in production > environment anyway so we cannot really rely on those. Having them in > WARN form would be still useful for debugging and those that really need > a crash dump while debugging can achieve the same result. One question is if we should be VM_WARN_ON vs. VM_WARN_ON_ONCE ... VM_BUG_ON is essentially a "once" thing so far, but then, we don't continue ... so probably most should be _ONCE. > > So while I agree that many of them could be dropped or made more clear > those could be dealt with after a mass move. An advantage of this would > be that we can drop VM_BUG_ON* and stop new instances from being added. As a first step we could probably just #define them to go to the VM_WARN_ON_* variants and see what happens. -- Cheers, David / dhildenb