Re: [PATCH 1/1] drm/i915: Fix for nested_enable_signaling BUG_ON

[John Harrison <John.C.Harrison@xxxxxxxxx>]

On 11/28/2017 1:40 AM, Chris Wilson wrote:

Quoting John.C.Harrison@xxxxxxxxx (2017-11-28 09:10:59)

From: John Harrison <John.C.Harrison@xxxxxxxxx>

The call to enable signaling was occuring after the request had been
sent to the GuC for execution on the hardware. That means that it is
possible for the request to actually complete before the code to
enable signaling has executed.

No, it wasn't, unless you had modified the code. Note also we switched
to a different scheme in upstream
-Chris

It was as of:

commit d99c1a7aff71536e909f54709023dcc5d6b559c0
Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Date:   Thu Mar 16 12:56:18 2017 +0000

drm/i915/scheduler: emulate a scheduler for guc

The code introduced was:

+               ...
+               if (last && rq->ctx != last->ctx) {
+                       ...
+                       nested_enable_signaling(last);
+                       port++;
+               }
+               ...
+               i915_guc_submit(rq);
+               last = rq;
+               submit = true;
+       }
+       if (submit) {
+               i915_gem_request_assign(&port->request, last);
+               nested_enable_signaling(last);
+               engine->execlist_first = rb;
+       }
+       ...

That quite definitely calls nested_enable_signaling() after calling i915_guc_submit(). It is either called on the last request submitted for a given context or on the last request submitted overall. But in either case it is only called after the actual submission occurs.

Maybe that was not exactly 4.11, there might have been a few more recent patches pulled in to this tree. It is definitely not latest upstream though. And as I noted in the cover letter, moving to latest upstream is not an option for them at this point.

John.

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