linux-kernel - Re: BUG: MAX_LOCKDEP_CHAIN

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Message-ID: <a8992f62-06e6-b183-3ab5-8118343efb3f@redhat.com>
Date:   Thu, 26 Jan 2023 19:20:25 -0500
From:   Waiman Long <longman@...hat.com>
To:     Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>,
        Boqun Feng <boqun.feng@...il.com>
Cc:     dsterba@...e.cz, Btrfs BTRFS <linux-btrfs@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Chris Murphy <lists@...orremedies.com>,
        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 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.

Cheers,
Longman