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From:   Qian Cai <cai@lca.pw>
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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: <CACT4Y+ZE1XhYpTsjP1J1PyUsEHYKvchww71aHb7UnSk5=4xUrw@mail.gmail.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Xu <peterx@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, Jens Axboe <axboe@kernel.dk>,
        Christoph Lameter <cl@linux.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Dan Rue <dan.rue@linaro.org>
In-Reply-To: <CACT4Y+ZE1XhYpTsjP1J1PyUsEHYKvchww71aHb7UnSk5=4xUrw@mail.gmail.com>
To:     Dmitry Vyukov <dvyukov@google.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Apr 14, 2020, at 7:13 AM, Dmitry Vyukov <dvyukov@google.com> 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.=