Re: [PATCH v7 09/12] drm/i915: add a new perf configuration execbuf parameter

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On 09/07/2019 14:06, Chris Wilson wrote:
Quoting Lionel Landwerlin (2019-07-09 11:59:31)
On 09/07/2019 12:58, Chris Wilson wrote:
Quoting Lionel Landwerlin (2019-07-09 10:32:05)
+static int eb_oa_config(struct i915_execbuffer *eb)
+{
+       int err;
+
+       if (!eb->oa_config)
+               return 0;
+
+       err = i915_active_request_set(&eb->engine->last_oa_config,
+                                     eb->request);
This is outside of the eb->request->timeline->mutex and needs a mutex.

Can I do this inside i915_request_add() when rq->flags &
I915_REQUEST_FLAGS_PERF ?
No. Because it is still being accessed without the appropriate locks.
(Multiple callers trying to modify eb->engine->last_oa_config all using
their own timeline->mutex.) You already need a lock to serialise
oa_config, that seems adequate to cover last_oa_config as well.

Oh, don't call the flag _PERF but something like FLAGS_NOPREEMPT so
it indicates the mechanism. Come to think of this don't include _FLAGS_
as we don't need to disambiguate yet :)
-Chris

Aligns perfectly ;)


-Lionel

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