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Fri, 19 Jul 2024 11:13:28 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id BcMlGVhKmmbWZQAAD6G6ig (envelope-from ); Fri, 19 Jul 2024 11:13:28 +0000 Message-ID: <4a1bd482-bfff-4843-a60f-004b3a8a99e4@suse.cz> Date: Fri, 19 Jul 2024 13:13:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC] mm: warn potential return NULL for kmalloc_array and kvmalloc_array with __GFP_NOFAIL Content-Language: en-US To: Michal Hocko Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, Barry Song , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com> References: <031ff35b-65f0-4ead-a08f-21711bad5e29@suse.cz> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Queue-Id: 5C694120015 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: mtouhxmszjfs76de6iy67timrrs7zaaf X-HE-Tag: 1721387610-66120 X-HE-Meta: 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 O4okpMot Yc79OTbm08mzGk0958Qquj4V/B7hPb70Mx/xnIxc20ndoLKoWcXaq7XWob1zmEVNSfh7Ecb+eqOMFLUAMPV3gbXAI6F9EzR0WmwCJKDfU3vx2tA0l8EUwdctcHLPThlJUgLY5DuvAnBn0UeRqiUDIstZQFtpcnyp+9AfTtrIeq9V/1wk0KlIirA0/UfSGFLXXHhbDJ9ompiHi7f7bU5sxI/N1TSw1dnsoWSKughTq6qPr6bsb9OUM7LKspcKE4sDWUG6E2bhN8QWKJy46W0nQeyEYfN1TZL2RU/NObGyQ4XXNnkuCO1/qUSUGaWAJ/sDML75Wgko9OvYh91uwc0oeEmsBWH8pg/td3GQGLTFIYjAFTk9QAzapI3uoHrtymHh5EnO/ 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 7/19/24 12:52 PM, Michal Hocko wrote: > On Fri 19-07-24 12:10:13, Vlastimil Babka wrote: >> On 7/19/24 11:33 AM, Michal Hocko wrote: >> > On Fri 19-07-24 10:50:07, Vlastimil Babka wrote: >> > [...] >> >> That wouldn't mean the busy loop is a correct and supported practice. It >> >> would just mean it's the least bad of the bad options we have to deal with >> >> an allocation that's wrong but we didn't catch soon enough in the development. >> > >> > So you want to make those potential BUG_ONs hard/soft lockups (not sure >> > all arches have a reliable detection) instead? >> >> I'd expect on a SMP machine there's fair chance of being rescued by kswapd >> or other direct reclaimer. > > I would expect hard/soft lockups... Anyway, the question remains. What > is the preferred way to express this is not really supported scenario. The documentation and warnings? I don't think the warnings are failing us fundamentally. We could limit the corner cases where the are not being reached in case a buggy code is being executed (maybe only in some debug config if the checks would be too intrusive for a fast path otherwise). That would leave the corner cases where the buggy code is executed rarely. Maybe Christoph's suggestion for a build-time check would catch some of those.