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

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Message-ID: <20210325182046.GA15860@willie-the-truck>
Date:   Thu, 25 Mar 2021 18:20:47 +0000
From:   Will Deacon <will@...nel.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
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>
Subject: Re: [syzbot] BUG: soft lockup in do_wp_page (4)

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]

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