Quoting Sagar Arun Kamble (2018-01-22 10:38:10)
>
>
> On 1/22/2018 3:46 PM, Chris Wilson wrote:
> > 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.
> Do you mean locking between relay_create and relay_destroy?
We need a lock around guc->log.runtime.relay_chan as the destroy path is
not ostensibly serialised between multiple potential callers. Ordinarily
I would have said that serialisation for create/destroy/access of
relay_chan was guaranteed by init/fini ordering, but that's no longer
clear (based on a 5min read of the patch).
The most important question is "can relay_destroy be called while some
user still has access to the relay_chan?"
> > Looks like at the
> > moment, _create is using struct_mutex,
> relay_create and relay_destroy are now to be done outside of struct_mutex.
> I will add this documentation to the functions.
(lockdep_assert_held :)
-Chris
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