Re: [PATCH] drm/amdgpu: avoid null dereference of fence when using cpu to update page tables

[Lang Yu <Lang.Yu@amd.com>]

On 05/05/ , Christian König wrote:
> Am 05.05.23 um 11:10 schrieb Lang Yu:
> > Using cpu to update page tables is sychronous, no need to wait fence
> > and it is NULL in such a case.
> 
> Good catch, be we usually install the stub into fence pointers when they are
> unused. See dma_fence_get_stub().

Got it. Thanks for your suggestions.

Regards,
Lang

> Christian.
> 
> > 
> > Signed-off-by: Lang Yu <Lang.Yu@amd.com>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c
> > index f0f00466b59f..197981c4ac7d 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mes.c
> > @@ -1043,8 +1043,11 @@ int amdgpu_mes_add_ring(struct amdgpu_device *adev, int gang_id,
> >   	amdgpu_mes_ring_to_queue_props(adev, ring, &qprops);
> > -	dma_fence_wait(gang->process->vm->last_update, false);
> > -	dma_fence_wait(ctx_data->meta_data_va->last_pt_update, false);
> > +	if (gang->process->vm->last_update)
> > +		dma_fence_wait(gang->process->vm->last_update, false);
> > +	if (ctx_data->meta_data_va->last_pt_update)
> > +		dma_fence_wait(ctx_data->meta_data_va->last_pt_update, false);
> > +
> >   	amdgpu_mes_unlock(&adev->mes);
> >   	r = amdgpu_mes_add_hw_queue(adev, gang_id, &qprops, &queue_id);
>