Hi Philipp,
On Thu, 2026-07-09 at 14:32 +0200, Philipp Stanner wrote:
> +Cc Danilo (who is currently concerned with drm_device life times)
>
> On Wed, 2026-07-08 at 16:22 +0100, André Draszik wrote:
> >
>
> […]
>
> > Link:
> > https://sashiko.dev/#/patchset/[email protected]?part=1
> > Signed-off-by: André Draszik <[email protected]>
>
> I am tempted to think that this also needs a Fixes and needs to be
> backported into stable kernels, doesn't it? Especially if the BUG_ON
> disappears in stable kernels.
Good point, thanks. I forgot to add this in and will try to find a reasonable
commit to relate to.
>
> > ---
> > drivers/gpu/drm/drm_crtc.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
> > index 63ead8ba6756..d55f1377ec36 100644
> > --- a/drivers/gpu/drm/drm_crtc.c
> > +++ b/drivers/gpu/drm/drm_crtc.c
> > @@ -501,6 +501,12 @@ void drm_crtc_cleanup(struct drm_crtc *crtc)
> > {
> > struct drm_device *dev = crtc->dev;
> >
> > + /* Ensure our dma_fence_ops remain valid for an RCU grace period after
> > + * the fence is signaled. This is necessary because our dma_fence_ops
> > + * dereference crtc->dev.
> > + */
> > + synchronize_rcu();
>
> nit:
> I guess this is the only place where one can reasonably put the
> synchronize_rcu(). But I would hint at the RCU delay in the function's
> docu.
Unfortunately, this still looks like an incomplete fix -
https://sashiko.dev/#/patchset/[email protected]?part=1
My next version will simply copy the relevant strings into a custom
struct drm_crtc_fence {
struct dma_fence base;
char driver_name[32];
char timeline_name[32];
};
or similar as part of drm_crtc_create_fence() and just use those as part
of the dma_fence_ops. That approach should avoid all race conditions and
corner cases with RCU.
I'll also make sure to update relevant documentation.
Cheers,
Andre'
