linux-kernel - Re: [syzbot] BUG: MAX_LOCKDEP

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Message-ID: <208cd812-214f-ef2f-26ec-cc7a73953885@i-love.sakura.ne.jp>
Date:   Thu, 20 May 2021 14:02:00 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        David Miller <davem@...emloft.net>
Cc:     syzbot <syzbot+a70a6358abd2c3f9550f@...kaller.appspotmail.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>
Subject: Re: [syzbot] BUG: MAX_LOCKDEP_KEYS too low! (2)

On 2021/05/20 5:09, Dmitry Vyukov wrote:
> On Wed, May 19, 2021 at 9:58 PM Randy Dunlap <rdunlap@...radead.org> wrote:
>>
>> On 5/19/21 12:48 PM, Dmitry Vyukov wrote:
>>> On Wed, May 19, 2021 at 7:35 PM syzbot
>>> <syzbot+a70a6358abd2c3f9550f@...kaller.appspotmail.com> wrote:
>>>>
>>>> Hello,
>>>>
>>>> syzbot found the following issue on:
>>>>
>>>> HEAD commit:    b81ac784 net: cdc_eem: fix URL to CDC EEM 1.0 spec
>>>> git tree:       net
>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15a257c3d00000
>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=5b86a12e0d1933b5
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=a70a6358abd2c3f9550f
>>>>
>>>> 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+a70a6358abd2c3f9550f@...kaller.appspotmail.com
>>>>
>>>> BUG: MAX_LOCKDEP_KEYS too low!
>>>
>>
>> include/linux/lockdep.h
>>
>> #define MAX_LOCKDEP_KEYS_BITS           13
>> #define MAX_LOCKDEP_KEYS                (1UL << MAX_LOCKDEP_KEYS_BITS)
> 
> Ouch, so it's not configurable yet :(

I didn't try to make this value configurable, for

> Unless, of course, we identify the offender that produced thousands of
> lock classes in the log and fix it.

number of currently active locks should decrease over time.
If this message is printed, increasing this value unlikely helps.

We have https://lkml.kernel.org/r/c099ad52-0c2c-b886-bae2-c64bd8626452@ozlabs.ru
which seems to be unresolved.

Regarding this report, cleanup of bonding device is too slow to catch up to
creation of bonding device?

We might need to throttle creation of BPF, bonding etc. which involve WQ operation for clean up ?