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AJvYcCUFoybnZrCGI3Ky7HBCZImcl4nERt78dhF2zsekbyO9fP9B2MaTyvqXeSe4tVTp98FC0wOsWKzWF2fPOzRbhk9NxTc= X-Gm-Message-State: AOJu0Yz9byuJyD+czCGTyHywpGzKF3lYr6HcEgVGvBqYLVAQG3Xreexa 3hC2McKijk36VNW0OKmCzmUifPj3YDlRihY9xNtRAxQvawy62Uhtl8c74krMRmHR2RqRVBxj/OB Lr0pIWjtsBzqcP0aJfToRreYPU68= X-Google-Smtp-Source: AGHT+IHUtjljCQMJmY4V/mtJDb0ao9nMgNflcFBso8m2k1tVlYNjzCwynl+8QfQc5G/EBVx3scxzWqtjSviySWIRnfo= X-Received: by 2002:a05:6122:2186:b0:4d3:3846:73bb with SMTP id 71dfb90a1353d-4f4df6e50b5mr5349301e0c.7.1721292244612; Thu, 18 Jul 2024 01:44:04 -0700 (PDT) MIME-Version: 1.0 References: <20240717230025.77361-1-21cnbao@gmail.com> In-Reply-To: From: Barry Song <21cnbao@gmail.com> Date: Thu, 18 Jul 2024 20:43:53 +1200 Message-ID: Subject: Re: [PATCH RFC] mm: warn potential return NULL for kmalloc_array and kvmalloc_array with __GFP_NOFAIL To: Michal Hocko Cc: akpm@linux-foundation.org, linux-mm@kvack.org, Barry Song , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 825FB10000B X-Stat-Signature: qs1ozwr4xismnrmk6sq83mx7sj75ygsf X-Rspam-User: X-HE-Tag: 1721292245-945885 X-HE-Meta: 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 C1+hE+FK tZUwY0zXZBTAIfRV75SioOYtgymAgRr3d5UitoY3hWZAxuCL9s3Sndfe3u7j9UjRVAgUTcO3zuVfiSVy5Q38neFJKXGgcFn5XY8Duleekzf0rk+Hz5cJwQzT0R2Bwsbl5sIBMarE6CUHwRj1PGdyjGnm8PhIsBJLAys/W9kynDcIvBsvAuvvjghiulj5IW0XSog0rnosYcAyZsA/JjlNpMNItuEGha+nf/zl9y9LUObgIC4FTO1EW52xa0uu4hflRcvljNDBJYReUSui6NuGdoydZUxQxZzBydcM8amEbFPt8iSPamRiTMHf4GhYN06zaeQmpnh0aXnyhPBnGW8vpg3QiprtYOuifFK2kIgXQFnZ3ziqTrJ2S7Rv22Z6KaYzJC8x3yUCBijGOyiqHXvNYoScIUKL/cVwsHNlzXVvWd3sXjq4ynpjzypjsPOSTygIx/RKpSHdO3ku+uGZFok+Gl1b5mvPbqm2ELrsI 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 Thu, Jul 18, 2024 at 8:32=E2=80=AFPM Michal Hocko wrot= e: > > On Thu 18-07-24 20:18:02, Barry Song wrote: > > So the purpose is making sure the semantics - NOFAIL means no failure > > and we don't need to check ret. If we can't really succeed, it should = throw > > a BUG to stop any potential exploits. > > This would require to panic consistently on failure in all allocator > path that can bail out. E.g. page allocator on GFP_NOWAIT|GFP_NOFAIL > req. not sure how many more. Right, this GFP_NOFAIL issue seems quite messy. However, at least vmalloc will retry by itself, even if alloc_pages might have failed with GFP_NOWAIT | GFP_NOFAIL. But isn't that the definition of __GFP_NOFAIL? * %__GFP_NOFAIL: The VM implementation _must_ retry infinitely: the caller * cannot handle allocation failures. The allocation could block * indefinitely but will never return with failure. Testing for * failure is pointless." So I believe any code that doesn't retry and ends up returning NULL should = be fixed. Otherwise, we should rename __GFP_NOFAIL to __GFP_UNLIKELY_FAIL in the documentation and explain when it might fail. > -- > Michal Hocko > SUSE Labs Thanks Barry