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[209.85.167.47]) by smtp.gmail.com with ESMTPSA id e9sm5153959lfc.253.2020.12.27.15.40.52 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 27 Dec 2020 15:40:52 -0800 (PST) Received: by mail-lf1-f47.google.com with SMTP id y19so20330183lfa.13 for ; Sun, 27 Dec 2020 15:40:52 -0800 (PST) X-Received: by 2002:a2e:9ad7:: with SMTP id p23mr19677994ljj.465.1609112452213; Sun, 27 Dec 2020 15:40:52 -0800 (PST) MIME-Version: 1.0 References: <20201225113157.e7hmluffh56fszfc@box> <20201226204335.dikqkrkezqet6oqf@box> <20201226224016.dxjmordcfj75xgte@box> In-Reply-To: From: Linus Torvalds Date: Sun, 27 Dec 2020 15:40:36 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting To: Hugh Dickins , Andrew Morton Cc: Damian Tometzki , "Kirill A. Shutemov" , Matthew Wilcox , "Kirill A. Shutemov" , Will Deacon , Linux Kernel Mailing List , Linux-MM , Linux ARM , Catalin Marinas , Jan Kara , Minchan Kim , Vinayak Menon , Android Kernel Team Content-Type: text/plain; charset="UTF-8" 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: On Sun, Dec 27, 2020 at 3:12 PM Linus Torvalds wrote: > > Ok, your fix for that folded in, and here's yet another version. Still not good. I don't know what happened, but the change of - vm_fault_t ret = 0; + vm_fault_t ret; is very very wrong. The next user is + if (!(vma->vm_flags & VM_SHARED)) + ret = check_stable_address_space(vma->vm_mm); + if (ret) + return ret; so now 'ret' will potentially be used uninitialized (although this is the kind of thing that a compiler might almost accidentally end up fixing - with a single dominating assignment, I could imagine the compiler moving the test to that assignment and thus "fixing" the code without really even meaning to). I think Kirill was intending to move the "if (ret)" up into the path that sets it, IOW something like + if (!(vma->vm_flags & VM_SHARED)) { + ret = check_stable_address_space(vma->vm_mm); + if (ret) + return ret; + } instead. But that patch as-is is broken. Kirill? Linus