Am 06.02.24 um 15:29 schrieb Daniel Vetter:
On Fri, Feb 02, 2024 at 03:40:03PM -0800, Greg Kroah-Hartman wrote:
On Fri, Feb 02, 2024 at 05:25:56PM -0500, Hamza Mahfooz wrote:
Removing an amdgpu device that still has user space references allocated
to it causes undefined behaviour.
Then fix that please. There should not be anything special about your
hardware that all of the tens of thousands of other devices can't handle
today.
What happens when I yank your device out of a system with a pci hotplug
bus? You can't prevent that either, so this should not be any different
at all.
sorry, but please, just fix your driver.
fwiw Christian König from amd already rejected this too, I have no idea
why this was submitted
Well that was my fault.
I commented on an internal bug tracker that when sysfs bind/undbind is a
different code path from PCI remove/re-scan we could try to reject it.
Turned out it isn't a different code path.
since the very elaborate plan I developed with a
bunch of amd folks was to fix the various lifetime lolz we still have in
drm. We unfortunately export the world of internal objects to userspace as
uabi objects with dma_buf, dma_fence and everything else, but it's all
fixable and we have the plan even documented:
https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#device-hot-unplug
So yeah anything that isn't that plan of record is very much no-go for drm
drivers. Unless we change that plan of course, but that needs a
documentation patch first and a big discussion.
Aside from an absolute massive pile of kernel-internal refcounting bugs
the really big one we agreed on after a lot of discussion is that SIGBUS
on dma-buf mmaps is no-go for drm drivers, because it would break way too
much userspace in ways which are simply not fixable (since sig handlers
are shared in a process, which means the gl/vk driver cannot use it).
Otherwise it's bog standard "fix the kernel bugs" work, just a lot of it.
Ignoring a few memory leaks because of messed up refcounting we actually
got that working quite nicely.
At least hot unplug / hot add seems to be working rather reliable in our
internal testing.
So it can't be that messed up.
Regards,
Christian.
Cheers, Sima
