Re: [PATCH v2] drm/i915: Fixed NULL pointer dereference in capture_engine

[John Harrison <john.c.harrison@intel.com>]

On 11/20/2024 07:03, Eugene Kobyak wrote:
> When the intel_context structure contains NULL,
> it raises a NULL pointer dereference error in drm_info().
>
> This patch aims to resolve issue:
> https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12309
>
> Signed-off-by: Eugene Kobyak <eugene.kobyak@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_gpu_error.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index 135ded17334e..acf403e4e5d6 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -1643,9 +1643,12 @@ capture_engine(struct intel_engine_cs *engine,
>   		return NULL;
>   
>   	intel_engine_get_hung_entity(engine, &ce, &rq);
> -	if (rq && !i915_request_started(rq))
> +	if (rq && !i915_request_started(rq)) {
> +		u16 guc_id = ce ? ce->guc_id.id : 0;
Note that zero is a valid GuC id. You should either set it to -1 or 
actually make the print conditional to not include the id at all.

John.

> +
>   		drm_info(&engine->gt->i915->drm, "Got hung context on %s with active request %lld:%lld [0x%04X] not yet started\n",
> -			 engine->name, rq->fence.context, rq->fence.seqno, ce->guc_id.id);
> +			 engine->name, rq->fence.context, rq->fence.seqno, guc_id);
> +	}
>   
>   	if (rq) {
>   		capture = intel_engine_coredump_add_request(ee, rq, ATOMIC_MAYFAIL);