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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Wed, 20 Mar 2019 14:59:19 +0100
Message-ID: <CACT4Y+b-VNeKwgP9-x2YZJ08v0f=2C2SujVkgEmcQ+B-ZmmCLQ@mail.gmail.com>
Subject: Re: kernel panic: corrupted stack end in wb_workfn
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        syzbot <syzbot+ec1b7575afef85a0e5ca@syzkaller.appspotmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Qian Cai <cai@lca.pw>, David Miller <davem@davemloft.net>,
        guro@fb.com, Johannes Weiner <hannes@cmpxchg.org>,
        Josef Bacik <jbacik@fb.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, linux-sctp@vger.kernel.org,
        Mel Gorman <mgorman@techsingularity.net>,
        Michal Hocko <mhocko@suse.com>,
        netdev <netdev@vger.kernel.org>,
        Neil Horman <nhorman@tuxdriver.com>,
        Shakeel Butt <shakeelb@google.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Vladislav Yasevich <vyasevich@gmail.com>,
        Matthew Wilcox <willy@infradead.org>,
        Xin Long <lucien.xin@gmail.com>
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On Wed, Mar 20, 2019 at 11:59 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> On 2019/03/20 19:42, Dmitry Vyukov wrote:
> >> I mean, yes, I agree, kernel bug bisection won't be perfect. But do
> >> you see anything actionable here?
>
> Allow users to manually tell bisection range when
> automatic bisection found a wrong commit.
>
> Also, allow users to specify reproducer program
> when automatic bisection found a wrong commit.
>
> Yes, this is anti automation. But since automation can't become perfect,
> I'm suggesting manual adjustment. Even if we involve manual adjustment,
> the syzbot's plenty CPU resources for building/testing kernels is highly
> appreciated (compared to doing manual bisection by building/testing kernels
> on personal PC environments).

FTR: provided an extended answer here:
https://groups.google.com/d/msg/syzkaller-bugs/1BSkmb_fawo/DOcDxv_KAgAJ


> > I see the larger long term bisection quality improvement (for syzbot
> > and for everybody else) in doing some actual testing for each kernel
> > commit before it's being merged into any kernel tree, so that we have
> > less of these a single program triggers 3 different bugs, stray
> > unrelated bugs, broken release boots, etc. I don't see how reliable
> > bisection is possible without that.
> >
>
> syzbot currently cannot test kernels with custom patches (unless "#syz test:" requests).
> Are you saying that syzbot will become be able to test kernels with custom patches?

I mean if we start improving kernel quality over time so that we have
less of these a single program triggers 3 different bugs, stray
unrelated bugs, broken release boots, etc, it will improve bisection
quality for everybody (beside being hugely useful in itself).