Re: [PATCH 4/4] lockdep: make MAX_LOCK_DEPTH configurable from Kconfig

[Govindarajulu Varadarajan]

On Fri, 29 Sep 2017, Bjorn Helgaas wrote:

> On Thu, Sep 28, 2017 at 04:51:46PM -0700, Govindarajulu Varadarajan wrote:
> > On Thu, 28 Sep 2017, Peter Zijlstra wrote:
> >
> > > On Wed, Sep 27, 2017 at 02:42:20PM -0700, Govindarajulu Varadarajan wrote:
> > > > Make MAX_LOCK_DEPTH configurable. It is set to 48 right now. Number of
> > > > VFs under a PCI pf bus can exceed 48 and this disables lockdep.
> > > >
> > > > lockdep currently allows max of 63 held_locks.
> > >
> > > But why a config knob? Why not just raise the number to 64
> > > unconditionally? And is that sufficient; you only state 48 is
> > > insufficient, you don't actually state the VF limit.
> >
> > I did not want to change the default configuration for everyone.
> >
> > I will change it 63 unconditionally in v2 and resubmit the series.
>
> I'm not happy about having to increase MAX_LOCK_DEPTH based on a
> number of VFs.  I haven't had time to look at the locking strategy
> you're proposing, but it just doesn't feel right to have to take 50+
> locks for one operation.

I agree. I have sent V2 where we dont lock 50+ device_lock. Please have a look.