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[209.85.221.47]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a83838cefe0sm671270766b.47.2024.08.19.13.35.39 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Aug 2024 13:35:40 -0700 (PDT) Received: by mail-wr1-f47.google.com with SMTP id ffacd0b85a97d-371941bbfb0so2260638f8f.0 for ; Mon, 19 Aug 2024 13:35:39 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCVzom15GwqS9XvgvL5o7wlK+jTgIWWqYAbp1PjG6IYcFA5y0zvctM6RrEmTzshtqA+BrGit06HGSg==@kvack.org X-Received: by 2002:adf:fa4f:0:b0:368:37d0:c4ca with SMTP id ffacd0b85a97d-3719443c779mr7296213f8f.24.1724099738889; Mon, 19 Aug 2024 13:35:38 -0700 (PDT) MIME-Version: 1.0 References: <20240817062449.21164-1-21cnbao@gmail.com> <20240817062449.21164-4-21cnbao@gmail.com> <5654b71c-1d9d-4c48-b28b-664662da8897@redhat.com> <416ac265-ced2-4f90-a347-0a256edf7fdf@redhat.com> <54a4619d-e826-465e-9a0f-0a8f37798e15@redhat.com> <5424dfa3-03db-4a82-a08e-fb31285774b3@redhat.com> In-Reply-To: From: Linus Torvalds Date: Mon, 19 Aug 2024 13:35:21 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 3/4] mm: BUG_ON to avoid NULL deference while __GFP_NOFAIL fails To: David Hildenbrand Cc: Michal Hocko , 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, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev, Christoph Hellwig , Lorenzo Stoakes , Kees Cook , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Jason Wang , Maxime Coquelin , "Michael S. Tsirkin" , Xuan Zhuo Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A615C20005 X-Stat-Signature: 3mioshchj1iffumcjhdoh8f8jhhsxqsm X-Rspam-User: X-HE-Tag: 1724099743-978315 X-HE-Meta: U2FsdGVkX1+glexAlLw06xkkhiQXJKiVXQvT01AlVndKLxrPMQgXj2azGSDs6wWAON17pOGPRB/tnsqshl0mUrKssFv9YreelbYdy6bkDNx+me1BvYxGixPHtA/1sPcs1kKS47YAIz4En09dv/z5usyal6jyKP70YFbH2dKFaidSwYKtZxfw0e/IuJ12nN3QDnwMumYXo5f8/RVIwUr+DfAwku9Osiw52FBW7NeC346WRUHGb8DslOzW/Q3By7orrUS5GyoZNiW2HPJucNZ9THb0MElyyfF35TDFjoYUgbW6oaHd83Y9Qn8FD+llZF3q+8Pkv+jY6F1dSVrdtninlExiWqJFXYzJNC7ZNtHj2MicutyN0bRGf69JJ7+q4hs/17R0CgAqfMJLzXpG0i1ucGhkcMvzn9zhyXFYx663TCAa1OfW4sQXK70TaC+520W3fma4cr3jcQaDJ/YGJU3Zd4uhaPsHFPz2OoeQp80aD9PGdFD1Gy5pkihZ5KN97WZb5n6vTPTy37PzOfUAsouNacebVaZZIttn39VvFkvvy5GUniLfk/SF5c2CG0v5IfYjuhuvfQATti6tbG93D+Hs9AGVQ53Wplk+AFoEnNXc0Qd4/TyvIBlcnBDSJ2zqOJsi/k/moDELVyKjeJbJmf2eH++BtpniFuylJRSshwM/jNqDrfBjdEmu3IjOgkGTwOgQwZ5KN+VXiJD+VsuRnqz4dCTCU5hZ+gvKlplLnSxpJcXYCTFRG3j7o//vA3LH++SnY9dmrbqR0ajkLeGEEgtTzuIVpy8DqQycNHcpvMYjxFKtTs/soOZiltaz+WE+n6zHIRqMMhJWajzpqYYs7q/4Gyo2FZBUSWOi9zkqImifQcqnonYR8qP8Qfu2OJACkI/RTWEBvPyjRyURtpZO6P+3aZQATju8MWwL8S+tlXlFKH009xZz7g6Ymf7ZiO4MtKm1MHOmKMqXRV4/WxlArnZ jP3MI9bQ 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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 Mon, 19 Aug 2024 at 13:24, David Hildenbrand wrote: > > Right, "warn + loop forever" is one alternative where you could at least > keep the system alive to some degree. Maybe. Or it might just lock up the machine. For small allocations looping forever is probably fine, because in practice there's always *something* that can be thrown out. But anything larger than order-3 (handwavy, but that was our historical limit, I think, and we call it PAGE_ALLOC_COSTLY_ORDER) has to fail at _some_ point, and the caller setting GFP_NOFAIL is just fantasy and "Daddy, I want a pony", and should be ignored. With a WARN_ON_ONCE(), by all means, so that people can see who the fantasist is. Linus