On Tue, Aug 26, 2025 at 5:11 PM David Wu <david...@amd.com> wrote:
>
> On 2025-08-26 16:58, Alex Deucher wrote:
>
> On Tue, Aug 26, 2025 at 3:48 PM David (Ming Qiang) Wu <david....@amd.com>
> wrote:
>
> to_amdgpu_fence() could return NULL pointer which needs
> to be protected for dereferencing.
>
> I don't think any of these cases could ever be NULL. The amdgpu_fence
> is a container for the dma_fence so it will alway be present. See
> struct amdgpu_fence.
>
> hmmm... but - the function could return NULL based on base.ops - see below
> if it should never happen then we should remove the checking. I doubt we
> will ever return NULL, however someone knowledgeable PLEASE fix it properly.
> The patch is only to protect it just in case.
if you look at amdgpu_fence_emit() the fences will only be created
with either amdgpu_job_fence_ops or amdgpu_fence_ops so there is no
way it will be NULL. It's a false positive.
Alex
>
> static inline struct amdgpu_fence *to_amdgpu_fence(struct dma_fence *f)
>
> {
> struct amdgpu_fence *__f = container_of(f, struct amdgpu_fence, base);
>
> if (__f->base.ops == &amdgpu_fence_ops ||
> __f->base.ops == &amdgpu_job_fence_ops)
> return __f;
>
> return NULL;
> }
>
> Alex
>
> Signed-off-by: David (Ming Qiang) Wu <david....@amd.com>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 22 +++++++++++++++-------
> 1 file changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> index 2d58aefbd68a7..1432b64d379ef 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
> @@ -160,7 +160,9 @@ int amdgpu_fence_emit(struct amdgpu_ring *ring, struct
> dma_fence **f,
> }
> }
>
> - to_amdgpu_fence(fence)->start_timestamp = ktime_get();
> + am_fence = to_amdgpu_fence(fence);
> + if (am_fence)
> + am_fence->start_timestamp = ktime_get();
>
> /* This function can't be called concurrently anyway, otherwise
> * emitting the fence would mess up the hardware ring buffer.
> @@ -387,6 +389,7 @@ u64 amdgpu_fence_last_unsignaled_time_us(struct
> amdgpu_ring *ring)
> struct amdgpu_fence_driver *drv = &ring->fence_drv;
> struct dma_fence *fence;
> uint32_t last_seq, sync_seq;
> + struct amdgpu_fence *f;
>
> last_seq = atomic_read(&ring->fence_drv.last_seq);
> sync_seq = READ_ONCE(ring->fence_drv.sync_seq);
> @@ -399,8 +402,8 @@ u64 amdgpu_fence_last_unsignaled_time_us(struct
> amdgpu_ring *ring)
> if (!fence)
> return 0;
>
> - return ktime_us_delta(ktime_get(),
> - to_amdgpu_fence(fence)->start_timestamp);
> + f = to_amdgpu_fence(fence);
> + return f ? ktime_us_delta(ktime_get(), f->start_timestamp) : 0;
> }
>
> /**
> @@ -417,13 +420,16 @@ void amdgpu_fence_update_start_timestamp(struct
> amdgpu_ring *ring, uint32_t seq,
> {
> struct amdgpu_fence_driver *drv = &ring->fence_drv;
> struct dma_fence *fence;
> + struct amdgpu_fence *f;
>
> seq &= drv->num_fences_mask;
> fence = drv->fences[seq];
> if (!fence)
> return;
>
> - to_amdgpu_fence(fence)->start_timestamp = timestamp;
> + f = to_amdgpu_fence(fence);
> + if (f)
> + f->start_timestamp = timestamp;
> }
>
> /**
> @@ -827,7 +833,8 @@ static const char *amdgpu_fence_get_driver_name(struct
> dma_fence *fence)
>
> static const char *amdgpu_fence_get_timeline_name(struct dma_fence *f)
> {
> - return (const char *)to_amdgpu_fence(f)->ring->name;
> + struct amdgpu_fence *am_f = to_amdgpu_fence(f);
> + return (const char *) (am_f ? am_f->ring->name : "");
> }
>
> static const char *amdgpu_job_fence_get_timeline_name(struct dma_fence *f)
> @@ -847,8 +854,9 @@ static const char
> *amdgpu_job_fence_get_timeline_name(struct dma_fence *f)
> */
> static bool amdgpu_fence_enable_signaling(struct dma_fence *f)
> {
> - if
> (!timer_pending(&to_amdgpu_fence(f)->ring->fence_drv.fallback_timer))
> - amdgpu_fence_schedule_fallback(to_amdgpu_fence(f)->ring);
> + struct amdgpu_fence *am_f = to_amdgpu_fence(f);
> + if (am_f && !timer_pending(&am_f->ring->fence_drv.fallback_timer))
> + amdgpu_fence_schedule_fallback(am_f->ring);
>
> return true;
> }
> --
> 2.43.0
>
