Re: [PATCH] drm/gpuvm: take refcount on DRM device

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Apr 20, 2026 at 06:19:02PM +0200, Thomas Hellström wrote:
> On Mon, 2026-04-20 at 17:08 +0200, Danilo Krummrich wrote:
> > On Mon Apr 20, 2026 at 11:28 AM CEST, Thomas Hellström wrote:
> > > I agree with your reasoning here, but current fact is that most (if
> > > not
> > > all) holders of a drm device reference (files, pagemaps, dma-bufs)
> > > currently also hold a module reference to protect against this, and
> > > drm_gpuvm would be an outlier.
> > 
> > I'm not convinced; if the DRM device has the requirement to not
> > outlive the
> > module it is associated with, then the DRM device code has to take
> > care of this
> > requirement, and not every caller of drm_dev_get().
> > 
> > Besides that, if GPUVM holds the module reference count on behalf of
> > the DRM
> > device, it has the same effect that you rightfully point out below --
> > it breaks
> > rmmod.
> > 
> > > To fix this properly (lifting that requirement) one could introduce
> > > a
> > > drm device count in the module and have the module exit function
> > > wait
> > > for it to become zero, *and* that the code that did the last
> > > decrement
> > > finished executing.
> > > 
> > > https://patchwork.freedesktop.org/patch/712146/?series=163298&rev=1
> > 
> > This looks like a reasonable fix to me. And it makes me conclude that
> > we
> > basically agree on everything. :)
> 
> Yes, unless we'd want to do a similar wait for gpuvms before returning
> from the close() callback: If we assume all GPUVMs are tied to an open
> drm file, that would conceptually be nicer IMO but I agree if gpuvm
> drivers implement something like the above per-driver device count,
> that would be unnecessary.

Just to confirm, it sounds like no changes to my patch are required
here?

Alice