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[209.85.167.46]) by smtp.gmail.com with ESMTPSA id i16sm657930ljn.50.2020.07.15.14.36.02 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Jul 2020 14:36:03 -0700 (PDT) Received: by mail-lf1-f46.google.com with SMTP id j21so1939913lfe.6 for ; Wed, 15 Jul 2020 14:36:02 -0700 (PDT) X-Received: by 2002:ac2:548a:: with SMTP id t10mr505514lfk.142.1594848962528; Wed, 15 Jul 2020 14:36:02 -0700 (PDT) MIME-Version: 1.0 References: <20200715135011.42743-1-kirill.shutemov@linux.intel.com> <20200715205508.3rzrkhulruzpy6iv@box> In-Reply-To: <20200715205508.3rzrkhulruzpy6iv@box> From: Linus Torvalds Date: Wed, 15 Jul 2020 14:35:46 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCHv2] mm: Fix warning in move_normal_pmd() To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Andrew Morton , Linux-MM , Linux Kernel Mailing List , Naresh Kamboju , Joel Fernandes , William Kucharski Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 8E4AA1804E3A0 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 Wed, Jul 15, 2020 at 1:55 PM Kirill A. Shutemov wrote: > > I don't understand 'len' calculation in try_to_align_end(). Yeah, Joel found the same thing. You don't understand it, because it's garbage. > BUT > > I *think* there's a bigger problem with the patch: > > For stack relocation case both VMAs are the same and always(?) the only > VMA around at the time. It means none of ADDR_BEFORE_PREV and > ADDR_AFTER_NEXT are going to stop us. But for the stack relocation case, that should actually be fine. We are moving the whole thing. Or maybe I missed something. > Consider the following case, before and after try_to_align_start(): > > before after > old_addr: 0x0123000 0x0000000 > new_addr: 0x1123000 0x1000000 > len: 0x1000000 0x1123000 That's the "move up" case that fundamentally doesn't work anyway because it will corrupt the data as it moves it. The stack relocation only moves down. Linus