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[178.24.249.8]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5bec82e5eacsm4747177a12.19.2024.08.19.05.48.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Aug 2024 05:48:05 -0700 (PDT) Message-ID: Date: Mon, 19 Aug 2024 14:48:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/4] mm: prohibit NULL deference exposed for unsupported non-blockable __GFP_NOFAIL To: Michal Hocko Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, torvalds@linux-foundation.org, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev, Lorenzo Stoakes , Kees Cook , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Jason Wang , Maxime Coquelin , "Michael S. Tsirkin" , Xuan Zhuo References: <20240817062449.21164-1-21cnbao@gmail.com> <20240817062449.21164-5-21cnbao@gmail.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-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: D3B2C14002E X-Stat-Signature: hf4yfuifcsnjgs849pqnysrieg4cg9ee X-HE-Tag: 1724071689-809749 X-HE-Meta: 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 3lhY6+/B 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 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 19.08.24 12:19, Michal Hocko wrote: > On Mon 19-08-24 11:44:39, David Hildenbrand wrote: > [...] >>> if (gfp_mask & __GFP_NOFAIL) { >>> /* >>> - * All existing users of the __GFP_NOFAIL are blockable, so warn >>> - * of any new users that actually require GFP_NOWAIT >>> + * All existing users of the __GFP_NOFAIL are blockable >>> + * otherwise we introduce a busy loop with inside the page >>> + * allocator from non-sleepable contexts >>> */ >>> - if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) >>> - goto fail; >>> + BUG_ON(!can_direct_reclaim); >> >> No new BUG_ON(), WARN_ON_ONCE() is good enough for something that should be >> found during ordinary testing. > > Do you mean > if (WARN_ON_ONCE_GFP(...)) > goto retry? Not really ... but now I read the description more carefully and I am not sure why we are so into throwing around BUG_ONs here, for something that is simply not allowed and doesn't make sense. If __GFP_NOFAIL is documented to " + * It _must_ be blockable and used together with __GFP_DIRECT_RECLAIM. + * It should _never_ be used in non-sleepable contexts. " Why not document "__GFP_NOFAIL always implies __GFP_DIRECT_RECLAIM" and do exactly that? -- Cheers, David / dhildenb