Re: [PATCH] kvm/vfio: Fix potential deadlock on vfio group_lock

Jason Gunthorpe
2023-01-31T14:34:44Z

On Tue, Jan 31, 2023 at 09:27:54AM -0500, Anthony Krowiak wrote:
> I encountered a lockdep splat while running some regression tests today (see
> below). I suspected it might be this patch so I reverted it, rebuilt the
> kernel and ran the regression tests again; this time, the test ran cleanly.
> It looks like this patch may not have fixed the problem for which it was
> intended. Here is the relevant dmesg output:

Well, it fixes the deadlock it intended to fix and created another one
:)

It means device drivers cannot obtain the kvm lock from their open
functions in this new model.

Why does ap need to touch kvm->lock? (via get_update_locks_for_kvm)

Maybe you should split that lock and have a dedicated apcb lock?

Jason