[Intel-gfx] [PATCH 1/4] drm/i915/guc: Fix lockdep due to log relay channel handling under struct_mutex

[Chris Wilson]

Quoting Sagar Arun Kamble (2018-01-22 08:26:01)
> +int intel_guc_log_relay_create(struct intel_guc *guc)
> +{
> +       struct drm_i915_private *dev_priv = guc_to_i915(guc);
> +       struct rchan *guc_log_relay_chan;
> +       size_t n_subbufs, subbuf_size;
> +       int ret;
> +
> +       if (!i915_modparams.guc_log_level)
> +               return 0;
> +
> +       GEM_BUG_ON(guc_log_has_relay(guc));
> +
>          /* Keep the size of sub buffers same as shared log buffer */
> -       subbuf_size = guc->log.vma->obj->base.size;
> +       subbuf_size = GUC_LOG_SIZE;
>  
>         /* Store up to 8 snapshots, which is large enough to buffer sufficient
>          * boot time logs and provides enough leeway to User, in terms of
> @@ -407,33 +442,31 @@ static int guc_log_runtime_create(struct intel_guc *guc)
>                 DRM_ERROR("Couldn't create relay chan for GuC logging\n");
>  
>                 ret = -ENOMEM;
> -               goto err_vaddr;
> +               goto err;
>         }
>  
>         GEM_BUG_ON(guc_log_relay_chan->subbuf_size < subbuf_size);
>         guc->log.runtime.relay_chan = guc_log_relay_chan;
>  
> -       INIT_WORK(&guc->log.runtime.flush_work, capture_logs_work);
>         return 0;
>  
> -err_vaddr:
> -       i915_gem_object_unpin_map(guc->log.vma->obj);
> -       guc->log.runtime.buf_addr = NULL;
> +err:
> +       /* logging will be off */
> +       i915_modparams.guc_log_level = 0;
>         return ret;
>  }
>  
> -static void guc_log_runtime_destroy(struct intel_guc *guc)
> +void intel_guc_log_relay_destroy(struct intel_guc *guc)
>  {

Now exposed to multiple users, we need to document what the locking
requirements are here. Or add some local locking. Looks like at the
moment, _create is using struct_mutex, which as we are only handling the
relay may be overkill (but since this is one-off init, fair enough).
-Chris