drm/i915/gt: Add to timeline requires the timeline mutex

Modifying a remote context requires careful serialisation with requests
on that context, and that serialisation requires us to take their
timeline->mutex. Make it so.

Note that while struct_mutex rules, we can't create more than one
request in parallel, but that age is soon coming to an end.

v2: Though it doesn't affect the current users, contexts may share
timelines so check if we already hold the right mutex.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190725131447.27515-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index 9292b6ca5e9cd7e6de263c482a8fd076d80e57cf..d64b45f7ec6d1158687395b0170eff14bb10d3e9 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -254,10 +254,18 @@ int intel_context_prepare_remote_request(struct intel_context *ce,
        /* Only suitable for use in remotely modifying this context */
        GEM_BUG_ON(rq->hw_context == ce);
 
-       /* Queue this switch after all other activity by this context. */
-       err = i915_active_request_set(&tl->last_request, rq);
-       if (err)
-               return err;
+       if (rq->timeline != tl) { /* beware timeline sharing */
+               err = mutex_lock_interruptible_nested(&tl->mutex,
+                                                     SINGLE_DEPTH_NESTING);
+               if (err)
+                       return err;
+
+               /* Queue this switch after current activity by this context. */
+               err = i915_active_request_set(&tl->last_request, rq);
+               if (err)
+                       goto unlock;
+       }
+       lockdep_assert_held(&tl->mutex);
 
        /*
         * Guarantee context image and the timeline remains pinned until the
@@ -267,7 +275,12 @@ int intel_context_prepare_remote_request(struct intel_context *ce,
         * words transfer the pinned ce object to tracked active request.
         */
        GEM_BUG_ON(i915_active_is_idle(&ce->active));
-       return i915_active_ref(&ce->active, rq->fence.context, rq);
+       err = i915_active_ref(&ce->active, rq->fence.context, rq);
+
+unlock:
+       if (rq->timeline != tl)
+               mutex_unlock(&tl->mutex);
+       return err;
 }
 
 struct i915_request *intel_context_create_request(struct intel_context *ce)