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(p200300d82f199c0005687df700e1293d.dip0.t-ipconnect.de. [2003:d8:2f19:9c00:568:7df7:e1:293d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4526e055ff5sm30814785e9.8.2025.06.06.11.15.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Jun 2025 11:15:12 -0700 (PDT) Message-ID: <2f866f12-2aa0-4456-b215-08ddc9b13b1e@redhat.com> Date: Fri, 6 Jun 2025 20:15:10 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm/gup: remove (VM_)BUG_ONs To: Lorenzo Stoakes , John Hubbard Cc: Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Jason Gunthorpe , Peter Xu References: <20250604140544.688711-1-david@redhat.com> <1a65d0e6-6088-4a15-9c19-537203fe655c@redhat.com> <50ff9149-2824-4e57-8d74-d8d0c063c87e@lucifer.local> <1a7513cf-4a0a-4e58-b20d-31c1370b760f@lucifer.local> <72bb36f2-65b6-4785-af9d-5b1f8126fc78@lucifer.local> 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: <72bb36f2-65b6-4785-af9d-5b1f8126fc78@lucifer.local> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: JoKAvTNat3vmu-yDtbeGMgnBVNinRFyZyM_NTAIFsBY_1749233713 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 4C921A000F X-Rspamd-Server: rspam09 X-Stat-Signature: 5419fxxpd45155881qj1z9fzxreywgyb X-HE-Tag: 1749233716-633775 X-HE-Meta: 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 N2YWOIxH AniInikOpZ5XxhRb6f8PqmL+WDvf/G05u6UKdmLzBmORx6xw//JwBeN2fzDCNMmASuaIPr3pk7cFzrj5P6J1bALVggzsWzQoTwO8M2of1eBygScVmwcx8ynZ+ol2aikZB361m20IkHn3OPpJp5QA+hCADZsw6drtcg77v8O/Wf1iTnWGVwKMNxd+Fp4RcpX3g3f+5PSfsrSc3uCKab6tnLTNLj+2tkCG9eFIS+Qf4vINS8tMHoUQ4JcEWdERa8sNrRklpkMM0AJTMxBQAsJLPjqSGtfC9EdeXnPT1bcUD+vuKGXjXFn1IsWTi5nK0lQFByDRJI5VSdiyOzv4LOx0yUryQadVPsBwRxDNq5WMkVKxHIJw7/BzGyvIlnLIQozQqffMaUa0bAKQ9OMX4iJAK+Yfj4G1DX1IDCPLMswITmq+/bGio/8imjJw5LHx6H+kNgsdnF3+UcZ3QjFU= 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 20:06, Lorenzo Stoakes wrote: > On Fri, Jun 06, 2025 at 10:57:44AM -0700, John Hubbard wrote: >> On 6/6/25 4:04 AM, Lorenzo Stoakes wrote: >>> On Fri, Jun 06, 2025 at 12:28:28PM +0200, David Hildenbrand wrote: >>>> On 06.06.25 12:19, Lorenzo Stoakes wrote: >>>>> On Fri, Jun 06, 2025 at 12:13:27PM +0200, Michal Hocko wrote: >>>>>> On Fri 06-06-25 11:01:18, David Hildenbrand wrote: >>>>>>> On 06.06.25 10:31, Michal Hocko wrote: >>>>>> [...] >>> So to me the only assessment needed is 'do we want to warn on this or not?'. >>> >>> And as you say, really WARN_ON_ONCE() seems appropriate, because nearly always >>> we will get flooded with useless information. >>> >> >> As yet another victim of such WARN_ON() floods at times, I've followed >> this thread with great interest. And after reflecting on it a bit, I believe >> that, surprisingly enough, WARN_ON() is a better replacement for VM_BUG_ON() >> than WARN_ON_ONCE(), because: > > Right, these shouldn't be happening _at all_. > > I'm easy on this point, I'd say in that case VM_WARN_ON() is the most > _conservative_ approach, since these are things that must not happen, and > so it's not unreasonable to fail to repress repetitions of the 'impossible' > :) > > But I get the general point about ...WARN_ON_ONCE() avoiding floods. > > David, what do you think? Well, in this patch here I deliberately want _ONCE for the unpin sanity checks. Because if they start happening (IOW, now after 5 years observed for the first time?) I *absolutely don't* want to get flooded and *really* figure out what is going on by seeing what else failed. And crashing on VM_BUG_ON() and not observing anything else was also not particularly helpful :) Because ... they shouldn't be happening ... (well, it goes back to my initial point about requiring individual decisions etc ...) Not sure what's best now in the general case, in the end I don't care that much. Roll a dice? ;) -- Cheers, David / dhildenb