linux-kernel - Re: [syzbot] possible deadlock in del

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Message-ID: <CACT4Y+ZrkE=ZKKncTOJRJgOTNfU8PGz=k+8V+0602ftTCHkc6Q@mail.gmail.com>
Date:   Tue, 13 Apr 2021 20:24:00 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        syzkaller <syzkaller@...glegroups.com>
Cc:     syzbot <syzbot+61e04e51b7ac86930589@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, KVM list <kvm@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>, masahiroy@...nel.org,
        Ingo Molnar <mingo@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        rafael.j.wysocki@...el.com,
        Sean Christopherson <seanjc@...gle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Will Deacon <will@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [syzbot] possible deadlock in del_gendisk

On Tue, Apr 13, 2021 at 7:43 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 13 Apr 2021 13:41:47 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
>
> > As the below splats look like it has nothing to do with this patch, and
> > this patch will add a WARN() if there's broken logic somewhere, I bet the
> > bisect got confused (if it is automated and does a panic_on_warning),
> > because it will panic for broken code that his patch detects.
> >
> > That is, the bisect was confused because it was triggering on two different
> > issues. One that triggered the reported splat below, and another that this
> > commit detects and warns on.
>
> Is it possible to update the the bisect to make sure that if it is failing
> on warnings, to make sure the warnings are somewhat related, before decided
> that its the same bug?

It does not seem to be feasible, bugs manifest differently in both
space and time. Also even if we somehow conclude the crash we see is
different, it says nothing about the original bug. For more data see:
https://groups.google.com/g/syzkaller/c/sR8aAXaWEF4/m/tTWYRgvmAwAJ