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[209.85.167.43]) by smtp.gmail.com with ESMTPSA id k28-20020ac2457c000000b004fb9fbdd8fcsm2924350lfm.252.2023.07.04.10.13.33 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Jul 2023 10:13:34 -0700 (PDT) Received: by mail-lf1-f43.google.com with SMTP id 2adb3069b0e04-4f96d680399so8868312e87.0 for ; Tue, 04 Jul 2023 10:13:33 -0700 (PDT) X-Received: by 2002:a05:6512:3487:b0:4f8:565e:f4ae with SMTP id v7-20020a056512348700b004f8565ef4aemr10130538lfr.39.1688490813644; Tue, 04 Jul 2023 10:13:33 -0700 (PDT) MIME-Version: 1.0 References: <000000000000b73abf05ffa60902@google.com> <20230704092451.72974b7a62ae08d48c077e10@linux-foundation.org> <20230704170144.GB1851@sol.localdomain> In-Reply-To: <20230704170144.GB1851@sol.localdomain> From: Linus Torvalds Date: Tue, 4 Jul 2023 10:13:17 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [syzbot] [mm?] WARNING in __gup_longterm_locked To: Eric Biggers Cc: Andrew Morton , syzbot , linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: C981A100020 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 59539bwbxqsxfknypsgttcr8enhk868e X-HE-Tag: 1688490816-688093 X-HE-Meta: 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 b9EVWWiX 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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 Tue, 4 Jul 2023 at 10:01, Eric Biggers wrote: > > syzkaller just makes system calls. > > Unless you want to do the crazy thing of checking if current->comm begins with > "syz", I don't think there is a way to distinguish. Yeah, that's what I thought. > In the past there's been some discussion of adding a kconfig option like > CONFIG_FUZZ_TESTING that would be expected to be enabled in order to run a > kernel fuzzer, and changing behavior in certain cases based on that. Changing > behavior in production vs. test is problematic, though... Agreed. The whole point of a fuzzer is to check the real thing. This test for GUP expansion really is a pretty specialized thing. Maybe the WARN_ON_ONCE() could have been just a "pr_warn_once()", but at the same time, *if* that condition ever happens in some real situation, I'd really want to know just exactly *what* the app in question is doing. Linus