[03/17] drm/i915/gt: Unlock engine-pm after queuing the kernel context switch
diff mbox series

Message ID 20191119100929.2628356-3-chris@chris-wilson.co.uk
State New
Headers show
  • [01/17] drm/i915/gem: Manually dump the debug trace on GEM_BUG_ON
Related show

Commit Message

Chris Wilson Nov. 19, 2019, 10:09 a.m. UTC
In commit a79ca656b648 ("drm/i915: Push the wakeref->count deferral to
the backend"), I erroneously concluded that we last modify the engine
inside __i915_request_commit() meaning that we could enable concurrent
submission for userspace as we enqueued this request. However, this
falls into a trap with other users of the engine->kernel_context waking
up and submitting their request before the idle-switch is queued, with
the result that the kernel_context is executed out-of-sequence most
likely upsetting the GPU and certainly ourselves when we try to retire
the out-of-sequence requests.

As such we need to hold onto the effective engine->kernel_context mutex
lock (via the engine pm mutex proxy) until we have finish queuing the
request to the engine.

v2: Serialise against concurrent intel_gt_retire_requests()

Fixes: a79ca656b648 ("drm/i915: Push the wakeref->count deferral to the backend")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
 drivers/gpu/drm/i915/gt/intel_engine_pm.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff mbox series

diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
index 3c0f490ff2c7..722d3eec226e 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
@@ -75,6 +75,7 @@  static inline void __timeline_mark_unlock(struct intel_context *ce,
 static bool switch_to_kernel_context(struct intel_engine_cs *engine)
+	struct intel_context *ce = engine->kernel_context;
 	struct i915_request *rq;
 	unsigned long flags;
 	bool result = true;
@@ -99,15 +100,13 @@  static bool switch_to_kernel_context(struct intel_engine_cs *engine)
 	 * retiring the last request, thus all rings should be empty and
 	 * all timelines idle.
-	flags = __timeline_mark_lock(engine->kernel_context);
+	flags = __timeline_mark_lock(ce);
-	rq = __i915_request_create(engine->kernel_context, GFP_NOWAIT);
+	rq = __i915_request_create(ce, GFP_NOWAIT);
 	if (IS_ERR(rq))
 		/* Context switch failed, hope for the best! Maybe reset? */
 		goto out_unlock;
-	intel_timeline_enter(i915_request_timeline(rq));
 	/* Check again on the next retirement. */
 	engine->wakeref_serial = engine->serial + 1;
@@ -116,13 +115,17 @@  static bool switch_to_kernel_context(struct intel_engine_cs *engine)
 	rq->sched.attr.priority = I915_PRIORITY_BARRIER;
+	__i915_request_queue(rq, NULL);
 	/* Release our exclusive hold on the engine */
-	__i915_request_queue(rq, NULL);
+	/* And finally expose our selfselves to intel_gt_retire_requests() */
+	intel_timeline_enter(ce->timeline);
 	result = false;
-	__timeline_mark_unlock(engine->kernel_context, flags);
+	__timeline_mark_unlock(ce, flags);
 	return result;