linux-kernel - Re: BUG: MAX_LOCKDEP_CHAIN

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Date:   Fri, 27 Jan 2023 10:35:51 +0500
From:   Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Chris Murphy <lists@...orremedies.com>,
        Waiman Long <longman@...hat.com>,
        David Sterba <dsterba@...e.cz>,
        Btrfs BTRFS <linux-btrfs@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!

On Fri, Jan 27, 2023 at 9:08 AM Boqun Feng <boqun.feng@...il.com> wrote:
>
> On Thu, Jan 26, 2023 at 10:37:56PM -0500, Chris Murphy wrote:
> >
> >
> > On Thu, Jan 26, 2023, at 7:20 PM, Waiman Long wrote:
> > > On 1/26/23 17:42, Mikhail Gavrilov wrote:
> > >>> I'm not sure whether these options are better than just increasing the
> > >>> number, maybe to unblock your ASAP, you can try make it 30 and make sure
> > >>> you have large enough memory to test.
> > >> About just to increase the LOCKDEP_CHAINS_BITS by 1. Where should this
> > >> be done? In vanilla kernel on kernel.org? In a specific distribution?
> > >> or the user must rebuild the kernel himself? Maybe increase
> > >> LOCKDEP_CHAINS_BITS by 1 is most reliable solution, but it difficult
> > >> to distribute to end users because the meaning of using packaged
> > >> distributions is lost (user should change LOCKDEP_CHAINS_BITS in
> > >> config and rebuild the kernel by yourself).
> > >
> > > Note that lockdep is typically only enabled in a debug kernel shipped by
> > > a distro because of the high performance overhead. The non-debug kernel
> > > doesn't have lockdep enabled. When LOCKDEP_CHAINS_BITS isn't big enough
> > > when testing on the debug kernel, you can file a ticket to the distro
> > > asking for an increase in CONFIG_LOCKDEP_CHAIN_BITS. Or you can build
> > > your own debug kernel with a bigger CONFIG_LOCKDEP_CHAIN_BITS.
> >
> > Fedora bumped CONFIG_LOCKDEP_CHAINS_BITS=17 to 18 just 6 months ago for debug kernels.
> > https://gitlab.com/cki-project/kernel-ark/-/merge_requests/1921
> >
> > If 19 the recommended value I don't mind sending an MR for it. But if
> > the idea is we're going to be back here talking about bumping it to 20
> > in six months, I'd like to avoid that.
> >
>
> How about a boot parameter then?

I would like this option.
This is better than rebuilding the kernel yourself and asking the
distribution's maintainers to increase this value.

Thanks.

-- 
Best Regards,
Mike Gavrilov.