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[209.85.208.48]) by smtp.gmail.com with ESMTPSA id e8-20020a1709062c0800b0098822e05539sm14662120ejh.191.2023.07.05.08.55.02 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Jul 2023 08:55:02 -0700 (PDT) Received: by mail-ed1-f48.google.com with SMTP id 4fb4d7f45d1cf-51bece5d935so8764414a12.1 for ; Wed, 05 Jul 2023 08:55:02 -0700 (PDT) X-Received: by 2002:aa7:d502:0:b0:51d:d1ca:eab9 with SMTP id y2-20020aa7d502000000b0051dd1caeab9mr12543171edq.32.1688572501752; Wed, 05 Jul 2023 08:55:01 -0700 (PDT) MIME-Version: 1.0 References: <202307041023.bcdbbfc0-oliver.sang@intel.com> In-Reply-To: From: Linus Torvalds Date: Wed, 5 Jul 2023 08:54:44 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [linus:master] [gup] a425ac5365: WARNING:at_mm/gup.c:#__get_user_pages To: John Hubbard Cc: kernel test robot , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 0C0DF1C0019 X-Stat-Signature: c4x6d5c8ka8tg7djp5w3ucs7bw6f73ta X-HE-Tag: 1688572504-221620 X-HE-Meta: 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 F+Gp78JE 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 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, 5 Jul 2023 at 00:27, John Hubbard wrote: > > So it boils down to this: crashpad is reading from a valid starting > address, inside the vma for the ld-linux-x86-64.so.2 file, but it reads > a full 4KB page's worth, which takes it past the end of that vma. > > And although the expand_stack() logic is there as part of the > __access_remote_vm() path, that logic ignores the size of the read! So > it slips past without trying to expand the stack. > > Note that while next vma is indeed the stack, it is 919 GB away--a very > large gap. Ok, that's just the warning being a bit too simplistic. For the case of a accessing past the end of the previous vma, old kernels wouldn't have expanded the stack either, because not only do we have a stack size ulimit, but even if you set that to infinity we leave a guard gap between the previous mapping and the stack and don't allow them to grow together. I made the warning be about "any access below the stack" rather than try to limit it, so your warning is basically a situation where no actual semantic change has happened, and it's just that the warning was overly broad. I'll tighten it up, and switch the WARN_ON_ONCE() to just do a "dump_stack()" so that it won't cause problems with the syzbot tests either. Linus