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>>   * drm_crtc_cleanup - Clean up the core crtc usage >>   * @crtc: CRTC to cleanup >>   * >> - * This function cleans up @crtc and removes it from the DRM mode setting >> - * core. Note that the function does *not* free the crtc structure itself, >> - * this is the responsibility of the caller. >> + * This function cleans up @crtc and removes it from the DRM mode setting core, >> + * after first waiting an RCU grace period to ensure @crtc->dev can safely be >> + * dereferenced by our dma_fence_ops. >> + * >> + * Note that the function does *not* free the crtc structure itself, this is the >> + * responsibility of the caller. >>   */ >>  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(); >> + >>   /* Note that the crtc_list is considered to be static; should we >>   * remove the drm_crtc at runtime we would have to decrement all >>   * the indices on the drm_crtc after us in the crtc_list. > > > Seems we forgot [1] this patch. Sorry about that. > > This fix also looks fine to me (for now) since it's what the dma_fence > contract currently demands. > > I'm a bit nervous about a synchronize_rcu() being in every cleanup > path, but I suspect it's the most reasonable thing to do now. > > Let's wait a day or two to see if anyone has fundamental objections. > Could someone with some CRTC knowledge give it an R-b? Otherwise I'd > push it this week. I just picked them up and I'm about to push them to drm-misc-fixes. Regards, Christian. > > > Regards, > Philipp > > > [1] https://lore.kernel.org/dri-devel/73fc12734386c9bebc9cf6d3cea4c5f8e125255e.camel@mailbox.org/T/#thttps://lore.kernel.org/dri-devel/73fc12734386c9bebc9cf6d3cea4c5f8e125255e.camel@mailbox.org/T/#t