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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id w27sm10924164qtc.18.2020.04.14.04.59.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Apr 2020 04:59:17 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Qian Cai Mime-Version: 1.0 (1.0) Subject: Re: [PATCH 0/2] mm: Two small fixes for recent syzbot reports Date: Tue, 14 Apr 2020 07:59:16 -0400 Message-Id: <04E78431-7B62-4FA1-8B1D-51DF7648D9C5@lca.pw> References: Cc: Linus Torvalds , Stephen Rothwell , Andrew Morton , Peter Xu , LKML , Linux-MM , Jens Axboe , Christoph Lameter , Johannes Weiner , syzkaller , Dan Rue In-Reply-To: To: Dmitry Vyukov X-Mailer: iPhone Mail (17D50) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Apr 14, 2020, at 7:13 AM, Dmitry Vyukov wrote: >=20 > 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 en= abled, so would miss that ovs rcu-list lockdep warning. Same for that use-af= ter-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 Paul o= r Steve to pull out the commit which enabling rcu-list debugging by default w= ith PROVE_RCU. I learned through that restricted kconfig to some degree of minimal could sa= ve a lot of troubles late on especially those options that I have no way to e= xercise like net/bluetooth and sound currently. It is going to be extra work= s though because those default options in Linux-next or even defconfigs are n= ot always pleasant and would want to enable something I don=E2=80=99t need i= f not given human intervention.=