linux-kernel - Re: BUG: MAX_LOCKDEP

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Date:   Mon, 13 Jan 2020 12:11:23 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Cong Wang <xiyou.wangcong@...il.com>, ap420073@...il.com
Cc:     syzbot <syzbot+aaa6fa4949cc5d9b7b25@...kaller.appspotmail.com>,
        Ingo Molnar <mingo@...nel.org>,
        Will Deacon <will.deacon@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: BUG: MAX_LOCKDEP_CHAINS too low!

On Thu, Jan 9, 2020 at 11:59 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Fri, Sep 28, 2018 at 9:56 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > >> > Hello,
> > >> >
> > >> > syzbot found the following crash on:
> > >> >
> > >> > HEAD commit:    c307aaf3eb47 Merge tag 'iommu-fixes-v4.19-rc5' of git://gi..
> > >> > git tree:       upstream
> > >> > console output: https://syzkaller.appspot.com/x/log.txt?x=13810df1400000
> > >> > kernel config:  https://syzkaller.appspot.com/x/.config?x=dfb440e26f0a6f6f
> > >> > dashboard link: https://syzkaller.appspot.com/bug?extid=aaa6fa4949cc5d9b7b25
> > >> > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > >> >
> > >> > Unfortunately, I don't have any reproducer for this crash yet.
> > >> >
> > >> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > >> > Reported-by: syzbot+aaa6fa4949cc5d9b7b25@...kaller.appspotmail.com
> > >>
> > >> +LOCKDEP maintainers,
> > >>
> > >> What does this BUG mean? And how should it be fixed?
> > >>
> > >> Thanks
> > >>
> > >> > BUG: MAX_LOCKDEP_CHAINS too low!
> > >
> > > Is the his result of endlessly loading and unloading modules?
> > >
> > > In which case, the fix is: don't do that then.
> >
> > No modules involved, we don't have any modules in the image. Must be
> > something else.
> > Perhaps syzkaller just produced a workload so diverse that nobody ever produced.
>
> Peter, Ingo,
>
> This really plagues syzbot testing for more than a year now. These four:
>
> BUG: MAX_LOCKDEP_KEYS too low!
> https://syzkaller.appspot.com/bug?id=8a18efe79140782a88dcd098808d6ab20ed740cc
>
> BUG: MAX_LOCKDEP_ENTRIES too low!
> https://syzkaller.appspot.com/bug?id=3d97ba93fb3566000c1c59691ea427370d33ea1b
>
> BUG: MAX_LOCKDEP_CHAINS too low!
> https://syzkaller.appspot.com/bug?id=bf037f4725d40a8d350b2b1b3b3e0947c6efae85
>
> BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> https://syzkaller.appspot.com/bug?id=381cb436fe60dc03d7fd2a092b46d7f09542a72a
>
>
> Now running testing I only see a stream of different lockdep bugs mostly:
>
> 2020/01/09 11:41:51 vm-13: crash: BUG: MAX_LOCKDEP_ENTRIES too low!
> 2020/01/09 11:43:09 vm-9: crash: INFO: task hung in register_netdevice_notifier
> 2020/01/09 11:44:00 vm-26: crash: no output from test machine
> 2020/01/09 11:44:11 vm-8: crash: BUG: MAX_LOCKDEP_ENTRIES too low!
> 2020/01/09 11:44:28 vm-19: crash: BUG: MAX_LOCKDEP_ENTRIES too low!
> 2020/01/09 11:46:20 vm-27: crash: BUG: MAX_LOCKDEP_ENTRIES too low!
> 2020/01/09 11:46:41 vm-15: crash: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> 2020/01/09 11:46:45 vm-28: crash: BUG: MAX_LOCKDEP_ENTRIES too low!
> 2020/01/09 11:46:47 vm-29: crash: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> 2020/01/09 11:46:49 vm-22: crash: BUG: MAX_LOCKDEP_ENTRIES too low!
> 2020/01/09 11:46:50 vm-10: crash: no output from test machine
> 2020/01/09 11:46:52 vm-18: crash: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> 2020/01/09 11:46:53 vm-23: crash: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> 2020/01/09 11:47:17 vm-20: crash: lost connection to test machine
> 2020/01/09 11:47:48 vm-5: crash: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> 2020/01/09 11:47:56 vm-14: crash: WARNING in restore_regulatory_settings
> 2020/01/09 11:48:19 vm-2: crash: BUG: MAX_LOCKDEP_ENTRIES too low!
> 2020/01/09 11:48:21 vm-7: crash: BUG: MAX_LOCKDEP_ENTRIES too low!
> 2020/01/09 11:48:22 vm-3: crash: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> 2020/01/09 11:48:40 vm-25: crash: BUG: MAX_LOCKDEP_CHAINS too low!
>
> Should we just bump the limits there?
>
> Or are there some ID leaks in lockdep? syzbot has a bunch of very
> simple reproducers for these bugs, so not really a maximally diverse
> load. And I think I saw these bugs massively when testing just a
> single subsystem too, e.g. netfilter.

+Taehee, Cong,

In the other thread Taehee mentioned the creation of dynamic keys for
net devices that was added recently and that they are subject to some
limits.
syzkaller creates lots of net devices for isolation (several dozens
per test process, but then these can be created and destroyed
periodically). I wonder if it's the root cause of the lockdep limits
problems?