Re: BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!

[Waiman Long]

On 1/26/23 23:07, Boqun Feng 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?

A boot parameter doesn't work for a statically allocated array which is 
determined at compile time. Dynamic memory allocation isn't enabled yet 
at early boot when lockdep will be used.

Cheers,
Longman