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Tue, 14 Apr 2020 05:05:33 -0700 (PDT) MIME-Version: 1.0 References: <04E78431-7B62-4FA1-8B1D-51DF7648D9C5@lca.pw> In-Reply-To: <04E78431-7B62-4FA1-8B1D-51DF7648D9C5@lca.pw> From: Dmitry Vyukov Date: Tue, 14 Apr 2020 14:05:21 +0200 Message-ID: Subject: Re: [PATCH 0/2] mm: Two small fixes for recent syzbot reports To: Qian Cai Cc: Linus Torvalds , Stephen Rothwell , Andrew Morton , Peter Xu , LKML , Linux-MM , Jens Axboe , Christoph Lameter , Johannes Weiner , syzkaller , Dan Rue Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000084, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 14, 2020 at 1:59 PM Qian Cai wrote: > > On Apr 14, 2020, at 7:13 AM, Dmitry Vyukov wrote: > > > > How do these use-after-free's and locking bugs get past the > > unit-testing systems (which syzbot is not) and remain unnoticed for so > > long?... > > syzbot uses the dumbest VMs (GCE), so everything it triggers during > > boot should be triggerable pretty much everywhere. > > There are many reasons that any early testing would not be able to catch = ALL the syzbot blockers. > > The Kconfigs are different. For example, I don=E2=80=99t have openvswitch= enabled, so would miss that ovs rcu-list lockdep warning. Same for that us= e-after-free in net/bluetooth and a warning in sound subsystem. > > But, notifying Linux-next ML is a good start, so at least we could ask Pa= ul or Steve to pull out the commit which enabling rcu-list debugging by def= ault with PROVE_RCU. > > I learned through that restricted kconfig to some degree of minimal could= save a lot of troubles late on especially those options that I have no way= to exercise like net/bluetooth and sound currently. It is going to be extr= a works though because those default options in Linux-next or even defconfi= gs are not always pleasant and would want to enable something I don=E2=80= =99t need if not given human intervention. We only try to enable what we can reach. There is significant reach for sound and net/bluetooth even without any hardware. So I would assume generic testing systems like KernelCI, LKFT, CKI should enable these as well. Hopefully we don't have all of the sound and net/bluetooth completely untested in linux-next.