Re: [PATCH AUTOSEL 5.10 13/22] drm/amdgpu: install stub fence into potential unused fence pointers

From: Christian König
Date: Thu Aug 31 2023 - 09:26:58 EST


Am 31.08.23 um 12:56 schrieb Greg KH:
On Thu, Aug 31, 2023 at 12:27:27PM +0200, Christian König wrote:
Am 30.08.23 um 20:53 schrieb Chia-I Wu:
On Sun, Jul 23, 2023 at 6:24 PM Sasha Levin <sashal@xxxxxxxxxx> wrote:
From: Lang Yu <Lang.Yu@xxxxxxx>

[ Upstream commit 187916e6ed9d0c3b3abc27429f7a5f8c936bd1f0 ]

When using cpu to update page tables, vm update fences are unused.
Install stub fence into these fence pointers instead of NULL
to avoid NULL dereference when calling dma_fence_wait() on them.

Suggested-by: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Lang Yu <Lang.Yu@xxxxxxx>
Reviewed-by: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
We start getting this warning spew on chromeos
Yeah because the older kernels still kept track of the last VM fence in the
syncobj.

This patch here should probably not have been back ported.

Why was that done anyway? The upstream commit doesn't have a CC stable and
this is only a bug fix for a new feature not present on older kernels.
It is part of the AUTOSEL process.

Could we prevent patches from being backported by adding a Fixes: tag?

Thanks,
Christian.