linux-kernel - Re: BUG: MAX_LOCKDEP_CHAIN

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Date:   Thu, 26 Jan 2023 14:47:42 +0500
From:   Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
To:     dsterba@...e.cz, boqun.feng@...il.com
Cc:     Btrfs BTRFS <linux-btrfs@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Chris Murphy <lists@...orremedies.com>
Subject: Re: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!

On Wed, Jan 25, 2023 at 10:21 PM David Sterba <dsterba@...e.cz> wrote:
>
> On Wed, Jan 25, 2023 at 01:27:48AM +0500, Mikhail Gavrilov wrote:
> > On Tue, Jul 26, 2022 at 9:47 PM David Sterba <dsterba@...e.cz> wrote:
> > >
> > > On Tue, Jul 26, 2022 at 05:32:54PM +0500, Mikhail Gavrilov wrote:
> > > > Hi guys.
> > > > Always with intensive writing on a btrfs volume, the message "BUG:
> > > > MAX_LOCKDEP_CHAIN_HLOCKS too low!" appears in the kernel logs.
> > >
> > > Increase the config value of LOCKDEP_CHAINS_BITS, default is 16, 18
> > > tends to work.
> >
> > Hi,
> > Today I was able to get the message "BUG: MAX_LOCKDEP_CHAIN_HLOCKS too
> > low!" again even with LOCKDEP_CHAINS_BITS=18 and kernel 6.2-rc5.
> >
> > ❯ cat /boot/config-`uname -r` | grep LOCKDEP_CHAINS_BITS
> > CONFIG_LOCKDEP_CHAINS_BITS=18
> >
> > [88685.088099] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
> > [88685.088124] turning off the locking correctness validator.
> > [88685.088133] Please attach the output of /proc/lock_stat to the bug report
> > [88685.088142] CPU: 14 PID: 1749746 Comm: mv Tainted: G        W    L
> >   -------  ---  6.2.0-0.rc5.20230123git2475bf0250de.38.fc38.x86_64 #1
> > [88685.088154] Hardware name: System manufacturer System Product
> > Name/ROG STRIX X570-I GAMING, BIOS 4408 10/28/2022
> >
> > What's next? Increase this value to 19?
>
> Yes, though increasing the value is a workaround so you may see the
> warning again.

Is there any sense in this WARNING if we would ignore it and every
time increase the threshold value?
May Be set 99 right away? Or remove such a check condition?

-- 
Best Regards,
Mike Gavrilov.