linux-kernel - Re: WARNING in mark

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Date:   Tue, 25 Jun 2019 16:10:10 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        syzbot <syzbot+a861f52659ae2596492b@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: WARNING in mark_lock

On Tue, Jun 25, 2019 at 4:01 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Jun 25, 2019 at 02:07:42PM +0200, Dmitry Vyukov wrote:
> > On Tue, Jun 25, 2019 at 1:06 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > On Tue, Jun 25, 2019 at 01:03:01PM +0200, Peter Zijlstra wrote:
> > > > On Tue, Jun 25, 2019 at 08:20:56AM +0200, Thomas Gleixner wrote:
> > > > > On Mon, 24 Jun 2019, syzbot wrote:
> > > >
> > > > > > syzbot found the following crash on:
> > > > > >
> > > > > > HEAD commit:    dc636f5d Add linux-next specific files for 20190620
> > > > > > git tree:       linux-next
> > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=162b68b1a00000
> > >
> > > syzcaller folks; why doesn't the above link include the actual kernel
> > > boot, but only the userspace bits starting at syzcaller start?
> > >
> > > I was trying to figure out the setup, but there's not enough information
> > > here.
> >
> > Hi Peter,
> >
> > Usually there is too much after-boot output, so boot output is evicted
> > anyway even if was preserved initially. Also usually it's not
> > important (this is the first time this comes up). And also
> > structurally boot is a separate procedure in syzkaller VM abstraction,
> > a machine is booted, output is analyzed for potential crashes, then
> > the machine is considered in a known good state and then some workload
> > is started as a separate procedure and new output capturing starts
> > from this point again.
>
> Ah, for my own machines I spool all serial console output to a file,
> everything is preserved until logrotate kills it after a week or so.
>
> There is no distinction between boot and anything else, everything that
> goes to serial (and I make sure everything does) lands together.
>
> > What info are you interested in? Can if be obtained after boot?
>
> I was interested in the kernel commandline; and in particular the
> nohz_full configuration if any.

We don't give nohz_full or anything similar. The command line
arguments are available here:
https://github.com/google/syzkaller/blob/master/dashboard/config/upstream-apparmor.cmdline
and few are here:
https://github.com/google/syzkaller/blob/master/tools/create-gce-image.sh#L211