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[209.85.218.52]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a9e56493effsm217673966b.3.2024.11.01.12.00.16 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Nov 2024 12:00:16 -0700 (PDT) Received: by mail-ej1-f52.google.com with SMTP id a640c23a62f3a-a86e9db75b9so318881966b.1 for ; Fri, 01 Nov 2024 12:00:16 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCVoww9CvBcJpEaHoKEgaKYc2InxOpwa8ZneGM7x6PTOiYMaHWqyDUu9bLnTvsox1OukT2dAJZsiLg==@kvack.org X-Received: by 2002:a17:906:da8e:b0:a9a:20f9:a402 with SMTP id a640c23a62f3a-a9e5089c0aemr795182566b.13.1730487616180; Fri, 01 Nov 2024 12:00:16 -0700 (PDT) MIME-Version: 1.0 References: <20241101184627.131391-1-lorenzo.stoakes@oracle.com> In-Reply-To: <20241101184627.131391-1-lorenzo.stoakes@oracle.com> From: Linus Torvalds Date: Fri, 1 Nov 2024 08:59:58 -1000 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] mm: remove unnecessary page_table_lock on stack expansion To: Lorenzo Stoakes Cc: Andrew Morton , "Liam R . Howlett" , Vlastimil Babka , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 16251A002F X-Stat-Signature: t9gjmiu9dcx6jgfbo16rkgykw688dzhu X-Rspam-User: X-HE-Tag: 1730487598-22037 X-HE-Meta: U2FsdGVkX1+oC5G6DhEEjDha1D3ZnjSnT9WkqcmSonVn/msmCdx5A5LgZ/vk4z+rTaQj2jF0eVFLMczUaUMhninWZo3M6C6y2hhqNVoAiwK0jB+7g6Pf+CDNlx0JGBcann9Rru3YSgymNZMt5MDsk4LuUlB31ALitdyq61im4n9/Z/2recAT6JWxLqOc1Z+HvTPITfSZGXFIK1nlzU3dNVenQRkUmBDkf7hXgML+s/rqtMWZ3iGfaXPRnHnZNgd3iiVlZWFmb6YJKIM7vdMzEeYQh2Szg2ej/PoLYvQUxfWqMbd01QERXzyx/6c5GwfuaaJwi2E6viyRWXziCVdBicBOryD3Kgzgx+4CQl8m68S+x7TnOHqAVjMTMPrGH4TcUUbGhX2XgwSpBW/WgZz2OeoZ/L7GAsZpSpgEA1lqcOS1C0EBydy6B2bBuF7RTjYitET7DThWIFkSeD5lRkVYJNalUrVSIGPsQfyf12Ot2PfzPfYHvhQKIX7TM7odpb3bb/UqcDCGhNJlSwh8H+VEmyaJkYP2RCC+AaspS4KBVbpFof+7iEYBQMee8ghM6cbiAOuToy8h91Btr7KXWV0GobF6GZzZRM03Iaj4mEcjkcuQ2G8fmz7JNcHm1ZqGHeen8BIHbI7uKiVUU1jTOwNEPbI3XqVuPWJ2RGM+4oaUy8OJjzWsn57fCfyn8Ua3gQ8RqaL3erCGpJHIU+QENC8/L486Wj5J9u0qMLUyjzvDLOAoGZXt6mRfXg00PwKFnx40eVaVtUPvKNHCaudIR40X7AKUhPeZ1hY5f9qY3wq0XOjYkpJvZglN72VRcBF/s/Fs1kyXhnZSYhBzMktK69jMiSVCvDIpN3UgGXFiBW4FE3whmYCTBth51ui2H/bCY1lRRAGmVS2kkx+E1ZGosEKwjkoTLAPkB7IJW1JrgkFgydY4LKY7IbXEw2PduJ8u3Cv++TwskW0qFSxZbx+ZF8w 2y9kZxfA 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.010299, 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 Fri, 1 Nov 2024 at 08:46, Lorenzo Stoakes wrote: > > Each of which acquire the mmap write lock before doing so. Despite this, we > maintain code that acquires a page table lock in the expand_upwards() and > expand_downwards() code, stating that we hold a shared mmap lock and thus > this is necessary. > > It is not, we do not have to worry about concurrent VMA expansions so we > can simply drop this, and update comments accordingly. > > We do not even need be concerned with racing page faults, as > vma_start_write() is invoked in both cases. Ack, seems ObviouslyCorrect(tm). Linus