Re: [PATCH v4] drm/i915: Fix NULL pointer dereference in capture_engine

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

On 11/28/2024 13:28, Eugene Kobyak wrote:
> When the intel_context structure contains NULL,
> it raises a NULL pointer dereference error in drm_info().
>
> Fixes: e8a3319c31a1 ("drm/i915: Allow error capture without a request")
> Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12309
> Cc: John Harrison <John.C.Harrison@Intel.com>
> Cc: <stable@vger.kernel.org> # v6.3+
> Signed-off-by: Eugene Kobyak <eugene.kobyak@intel.com>
> ---
> v2:
>    - return drm_info to separate condition
> v3:
>    - create separate condition which generate string if intel_context exist
> v4:
>    - rollback and add check intel_context in log condition
>   drivers/gpu/drm/i915/i915_gpu_error.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index 135ded17334e..56f05a18870c 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -1643,7 +1643,7 @@ 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) && ce)
>   		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);
>   
But now you don't get a message when there is a request without the 
context pointer. Which can clearly happen because otherwise you wouldn't 
have hit a null pointer dereference in the first place.

John.