On 15/12/2016 20:54, Chris Wilson wrote:
> On Thu, Dec 15, 2016 at 11:44:13PM +0300, Dan Carpenter wrote:
>> Hello Tvrtko Ursulin,
>>
>> The patch a19d6ff29a82: "drm/i915: Small compaction of the engine
>> init code" from Jun 23, 2016, leads to the following static checker
>> warning:
>>
>> drivers/gpu/drm/i915/intel_lrc.c:1973 logical_render_ring_init()
>> warn: passing freed memory 'engine'
>>
>> drivers/gpu/drm/i915/intel_lrc.c
>> 1970
>> 1971 ret = logical_ring_init(engine);
>> 1972 if (ret) {
>> 1973 lrc_destroy_wa_ctx_obj(engine);
>>
>> The problem is that logical_ring_init() frees "engine" on the error
>> path so this is a use after free.
>
> And calls lrc_destroy_wa_ctx_obj() in the process. So we can
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c
> b/drivers/gpu/drm/i915/intel_lrc.c
> index 067394b0a769..1c1bad8ae7b0 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1940,12 +1940,7 @@ int logical_render_ring_init(struct intel_engine_cs
> *engine)
> ret);
> }
>
> - ret = logical_ring_init(engine);
> - if (ret) {
> - lrc_destroy_wa_ctx_obj(engine);
> - }
> -
> - return ret;
> + return logical_ring_init(engine);
> }
>
> int logical_xcs_ring_init(struct intel_engine_cs *engine)
>
I've marked this as TODO for later.
Interesting that it was detected only now. Even more so, the referenced
commit just moved the code around.
I think that the real issue was introduced around "drm/i915/gen8:
Re-order init pipe_control in lrc mode".
Regards,
Tvrtko
