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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1688490106; bh=LOPLcvVLj/Mftos4Uc1ZlZP/j0YoMDFVMwE2qCTIVdU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MV0V21XdkSVDK9kPGElVc5TfmbcDSdv3PxcpocLnqh4MF8MFHqIjhSa5kz3369wAn 4JzzzOoFV82MLOQoF/n8IEwP+UmxcgwBIE0aHkxFwt69nwrzazleFhc9i93BCcoMkV snQ94m4mwbae/Ir9+n7KuzYSu0PdQ4jZl4Jcug6X+vnjsJVkvWeoU8y2jx6tOLe6o9 Rql6GprOfN5W8EdXWfdqo8T/ZxmA7AHXnFH64wu9evLb0Eo7TDjqtOfQ1SLXZ2qu8G SyejXEBpjvhTCB+q+rM7vrAvgnukm12w/2CHCdLtXp18QwxZ1VsHYak8qrN1CynDWd cwsYwPwUucLfw== Date: Tue, 4 Jul 2023 10:01:44 -0700 From: Eric Biggers To: Linus Torvalds Cc: Andrew Morton , syzbot , linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [mm?] WARNING in __gup_longterm_locked Message-ID: <20230704170144.GB1851@sol.localdomain> References: <000000000000b73abf05ffa60902@google.com> <20230704092451.72974b7a62ae08d48c077e10@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 0316B18003A X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: nj976pd8tjnmxidk5x3ttnx4d7onhe7m X-HE-Tag: 1688490107-644898 X-HE-Meta: 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 fftQfDqU OdwIMjsfbLUKUqRj54rM8aTs4rNZFS56QFtgDWb+iIwBXGUaN99hhoCNtCK1apwFvIzASdY8lf52o8tHf8+lvQ8Mv7lcJw8YrQ4uL+HDQrDP1XxDAE1UXyUAAcQH+pvFsJJaBPt3t0yZ83y/ATHKJkWAgq0GiXbnZET0S0wmRgtvLGGF9reXvi0lnuavoXnm8jqZ0P8gED54ydTVix8LCIOmOrMwivxu2U8uC7XOnB4aMxNqm1w1lH2Qt6T60Elxebq6ikx5HrF20GaJn0hHIBnHUHOxxc789pfzjvsmPF/kSRRnqZ03dhm97Hf7O0pL9j6korrRzTGFK3xuLC33TNKhF2xBipdKtTeS/JU8AjAO6WgBggZ9aE1b2p4dGUx+k6TU+nirtpxSngpysVDi+AssGXK2Id+917GVhXqf+o73D6F+bYKE+/jQxQtsbn7neLKEN540VelXSC+FgEJQ9qsYmKQF0z4q4pVGNQhbCuMwa67Y= 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, Jul 04, 2023 at 09:39:48AM -0700, Linus Torvalds wrote: > On Tue, 4 Jul 2023 at 09:24, Andrew Morton wrote: > > > > Thanks. This is the temporary warning which was added by Linus's > > a425ac5365f6cb3cc4 ("gup: add warning if some caller would seem to want > > stack expansion"). > > Yes, and the randomizer system calls aren't very interesting for that warning. > > I don't have any good idea for how to distinguish "this is a > randomizer that is just doing crazy things by its very nature and is > passing in nonsensical system call arguments" from "this is a real > application that is doing crazy things that we will sadly have to try > to be backwards compatible with". > > And at the same time, I _really_ don't want that warning to then > perhaps hide some *other* more real warning from the test automation. > > End result: I'd love for that warning to trigger on real applications > (including ones run by any cloud test infrastructure, although I doubt > that infrastructure necessarily runs very interesting loads), but not > on things like syzbot and trinity that just randomize system calls. > > Does anybody have any ideas how to tell them apart? Maybe syzbot > already sets some flag for this purpose that I just haven't thought > of? > 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. 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... - Eric