linux-kernel - Re: [syzbot] BUG: soft lockup in do_wp

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Message-ID: <CACT4Y+Zq_cqJdcNA=rHXrEPhCxymW2cemmSCDTwikTn+wemUgg@mail.gmail.com>
Date:   Thu, 25 Mar 2021 20:08:18 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Will Deacon <will@...nel.org>
Cc:     syzbot <syzbot+0b036374a865ba0efa8e@...kaller.appspotmail.com>,
        kernel-team@...roid.com, Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: [syzbot] BUG: soft lockup in do_wp_page (4)

On Thu, Mar 25, 2021 at 7:34 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > On Thu, Mar 18, 2021 at 08:34:16PM +0100, Dmitry Vyukov wrote:
> > > On Thu, Mar 18, 2021 at 8:31 PM syzbot
> > > <syzbot+0b036374a865ba0efa8e@...kaller.appspotmail.com> wrote:
> > > >
> > > > Hello,
> > > >
> > > > syzbot found the following issue on:
> > > >
> > > > HEAD commit:    bf152b0b Merge tag 'for_linus' of git://git.kernel.org/pub..
> > > > git tree:       upstream
> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=17d5264ed00000
> > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=2c9917c41f0bc04b
> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=0b036374a865ba0efa8e
> > > > userspace arch: arm64
> > > >
> > > > Unfortunately, I don't have any reproducer for this issue yet.
> > > >
> > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > > Reported-by: syzbot+0b036374a865ba0efa8e@...kaller.appspotmail.com
> > > >
> > > > watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [syz-executor.1:3684]
> > >
> > > +Will, arm
> > >
> > > If I am reading this commit correctly, this is caused by:
> > >
> > > commit cae118b6acc309539b33339e846cbb19187c164c
> > > Author: Will Deacon
> > > Date:   Wed Mar 3 13:49:27 2021 +0000
> > >     arm64: Drop support for CMDLINE_EXTEND
> > >
> > > syzbot passes lots of critical things in CONFIG_CMDLINE:
> > > https://github.com/google/syzkaller/blob/c3c81c94865791469d376eba84f4a2d7763d3f71/dashboard/config/linux/upstream-arm64-kasan.config#L495
> > > but also wants the bootloader args to be appended.
> > > What is the way to do it now?
> >
> > For now, there isn't a way to do it with CONFIG_CMDLINE, so I think you can
> > either:
> >
> >   * Revert my patch for your kernels
> >   * Pass the arguments via QEMU's -append option
> >   * Take a look at one of the series which should hopefully add this
> >     functionality back (but with well-defined semantics) [1] [2]
>
> Unfortunately none of these work for syzbot (and I assume other
> testing environments).
>
> syzbot does not support custom patches by design:
> http://bit.do/syzbot#no-custom-patches
> As any testing system, it tests the official trees.
>
> It's not humans who start these VMs, so it's not as easy as changing
> the command line after typing...
> There is no support for passing args specifically to qemu, syzkaller
> support not just qemu, so these things are specifically localized in
> the config. Additionally there is an issue of communicating all these
> scattered details to developers in bug reports. Currently syzbot
> reports the kernel config and it as well captures command line.
>
> Could you revert the patch? Is there any point in removing the
> currently supported feature before the new feature lands?

FTR another instance:
https://syzkaller.appspot.com/bug?extid=b6c93d85a3f77fca7f13
https://lore.kernel.org/lkml/000000000000d7142c05be60db47@google.com/T/#u


> > Sorry for the nuisance; I did try to fix this [3] but it's a bit of a
> > mess.
> >
> > Will
> >
> > [1] https://lore.kernel.org/linux-arch/cover.1614705851.git.christophe.leroy@csgroup.eu/
> > [2] https://lore.kernel.org/linux-mips/20210308235319.2988609-2-danielwa@cisco.com/#t
> > [3] https://lore.kernel.org/r/20210225125921.13147-1-will@kernel.org