linux-kernel - Re: [PATCH 0/2] mm: Two small fixes for recent syzbot reports

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Message-Id: <04E78431-7B62-4FA1-8B1D-51DF7648D9C5@lca.pw>
Date:   Tue, 14 Apr 2020 07:59:16 -0400
From:   Qian Cai <cai@....pw>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Jens Axboe <axboe@...nel.dk>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Dan Rue <dan.rue@...aro.org>
Subject: Re: [PATCH 0/2] mm: Two small fixes for recent syzbot reports

> On Apr 14, 2020, at 7:13 AM, Dmitry Vyukov <dvyukov@...gle.com> 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’t have openvswitch enabled, so would miss that ovs rcu-list lockdep warning. Same for that use-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 Paul or Steve to pull out the commit which enabling rcu-list debugging by default 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 extra works though because those default options in Linux-next or even defconfigs are not always pleasant and would want to enable something I don’t need if not given human intervention.