Re: [bug report] WARNING: possible circular locking at: rdma_destroy_id+0x17/0x20 [rdma_cm] triggered by blktests nvmeof-mp/002

Jason Gunthorpe
2022-06-01T12:46:13Z

On Tue, May 31, 2022 at 10:55:46AM -0700, Bart Van Assche wrote:
> On 5/31/22 05:35, Jason Gunthorpe wrote:
> > On Sat, May 28, 2022 at 09:00:16PM +0200, Bart Van Assche wrote:
> > > On 5/27/22 14:52, Jason Gunthorpe wrote:
> > > > That only works if you can detect actual different lock classes during
> > > > lock creation. It doesn't seem applicable in this case.
> > >
> > > Why doesn't it seem applicable in this case? The default behavior of
> > > mutex_init() and related initialization functions is to create one lock
> > > class per synchronization object initialization caller.
> > > lockdep_register_key() can be used to create one lock class per
> > > synchronization object instance. I introduced lockdep_register_key() myself
> > > a few years ago.
> >
> > I don't think this should be used to create one key per instance of
> > the object which would be required here. The overhead would be very
> > high.
>
> Are we perhaps referring to different code changes? I'm referring to the
> code change below. The runtime and memory overhead of the patch below
> should be minimal.

This is not minimal, the lockdep graph will expand now with a node per
created CM ID ever created and with all the additional locking
arcs. This is an expensive operation.

AFIAK keys should not be created per-object like this but based on
object classes known when the object is created - eg a CM listening ID
vs a connceting ID as an example

This might be a suitable hack if the # of objects was small???

Jason