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[209.85.221.42]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a83839356e2sm678521266b.105.2024.08.19.15.14.14 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Aug 2024 15:14:14 -0700 (PDT) Received: by mail-wr1-f42.google.com with SMTP id ffacd0b85a97d-371afae614aso1553113f8f.0 for ; Mon, 19 Aug 2024 15:14:14 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCW0IqbSyfXftkcYvjCZ1tv2q+6YTraRFXIqR+JrHkCClwMUGncyrhFIRdJGNz4wL5RLywbj5S1N1w==@kvack.org X-Received: by 2002:adf:f012:0:b0:368:71fc:abb7 with SMTP id ffacd0b85a97d-37194446b13mr7177410f8f.16.1724105654263; Mon, 19 Aug 2024 15:14:14 -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> <6814fdf6-cf32-43e9-ba20-705ec5238abe@redhat.com> In-Reply-To: <6814fdf6-cf32-43e9-ba20-705ec5238abe@redhat.com> From: Linus Torvalds Date: Mon, 19 Aug 2024 15:13:57 -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: rspam12 X-Rspamd-Queue-Id: 4967B1C0010 X-Stat-Signature: iqcjhgzz6sy8ptx67kedem1uz3gpfxw5 X-Rspam-User: X-HE-Tag: 1724105657-542692 X-HE-Meta: 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 Y+6TXt17 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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 14:57, David Hildenbrand wrote: > > On 19.08.24 22:35, Linus Torvalds wrote: > > > > Maybe. Or it might just lock up the machine. > > Yes, regarding the security concerns it might be a bit better that way. > (no security expert, so I cannot judge ...) The thing is, in a static universe where time does not flow, that might be true. But in such a universe, we wouldn't actually be alive, much less do kernel development. In *REALITY*, security is not a single point in time. Real security is about the *future* more than it is about anything else. >From a user perspective, security is very much about things like "keep your system up-to-date", because we _know_ old systems have (known) bugs. But the other side of that is that from a developer perspective, the #1 thing in security is about fixing bugs. Yes, you want to be conservative so that bugs you haven't fixed yet don't cause problems, but that "be conservative" absolutely *has* to be priority #2. Because no amount of conservatism is going to help you unless you actively fix the bugs. And the thing is, a locked-up machine is really really hard to debug. I can tell you from experience just what the bug reports will look like, but I think you can guess. So locking up is one of the worst things you can do. You are pretty much always much better off making forward progress and try to report the issue. Including for security reasons. Because you'd rather have a security issue today that you can debug, and fix for tomorrow. A dead machine with a bug you can't debug is not actually suddenly a really secure machine. Because somebody will just figure out a way to take advantage of *that* bug too indirectly. Being able to kill machines at your leisure is a great way to stress other parts of your network, and suddenly that dead machine might be a big security hazard when somebody figures out a weakness elsewhere ("Oh, look, there's a bug in the fail-over that allows me to do X"). Linus