Re: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!

[Boqun Feng]

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?

Regards,
Boqun

> 
> 
> -- 
> Chris Murphy