[Intel-gfx] [PATCH v2 1/5] drm/i915: Fix request locking during error capture & debugfs dump

[John.C.Harrison@Intel.com]

From: John Harrison <John.C.Harrison@Intel.com>

When GuC support was added to error capture, the locking around the
request object was broken. Fix it up.

The context based search manages the spinlocking around the search
internally. So it needs to grab the reference count internally as
well. The execlist only request based search relies on external
locking, so it needs an external reference count. So no change to that
code itself but the context version does change.

The only other caller is the code for dumping engine state to debugfs.
That code wasn't previously getting an explicit reference at all as it
does everything while holding the execlist specific spinlock. So that
needs updaing as well as that spinlock doesn't help when using GuC
submission. Rather than trying to conditionally get/put depending on
submission model, just change it to always do the get/put.

In addition, intel_guc_find_hung_context() was not acquiring the
correct spinlock before searching the request list. So fix that up too.

Fixes: dc0dad365c5e ("drm/i915/guc: Fix for error capture after full GPU reset
with GuC")
Fixes: 573ba126aef3 ("drm/i915/guc: Capture error state on context reset")
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Cc: Michael Cheng <michael.cheng@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Cc: Bruce Chang <yu.bruce.chang@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
---
 drivers/gpu/drm/i915/gt/intel_context.c           |  1 +
 drivers/gpu/drm/i915/gt/intel_engine_cs.c         |  7 ++++++-
 drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 11 +++++++++++
 drivers/gpu/drm/i915/i915_gpu_error.c             |  5 ++---
 4 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index e94365b08f1ef..df64cf1954c1d 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -552,6 +552,7 @@ struct i915_request *intel_context_find_active_request(struct intel_context *ce)
 
 		active = rq;
 	}
+	active = i915_request_get_rcu(active);
 	spin_unlock_irqrestore(&parent->guc_state.lock, flags);
 
 	return active;
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 922f1bb22dc68..517d1fb7ae333 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -2236,10 +2236,13 @@ static void engine_dump_active_requests(struct intel_engine_cs *engine, struct d
 	guc = intel_uc_uses_guc_submission(&engine->gt->uc);
 	if (guc) {
 		ce = intel_engine_get_hung_context(engine);
-		if (ce)
+		if (ce) {
+			/* This will reference count the request (if found) */
 			hung_rq = intel_context_find_active_request(ce);
+		}
 	} else {
 		hung_rq = intel_engine_execlist_find_hung_request(engine);
+		hung_rq = i915_request_get_rcu(hung_rq);
 	}
 
 	if (hung_rq)
@@ -2250,6 +2253,8 @@ static void engine_dump_active_requests(struct intel_engine_cs *engine, struct d
 	else
 		intel_engine_dump_active_requests(&engine->sched_engine->requests,
 						  hung_rq, m);
+	if (hung_rq)
+		i915_request_put(hung_rq);
 }
 
 void intel_engine_dump(struct intel_engine_cs *engine,
diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index b436dd7f12e42..3b34a82d692be 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -4820,6 +4820,8 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
 
 	xa_lock_irqsave(&guc->context_lookup, flags);
 	xa_for_each(&guc->context_lookup, index, ce) {
+		bool found;
+
 		if (!kref_get_unless_zero(&ce->ref))
 			continue;
 
@@ -4836,10 +4838,18 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
 				goto next;
 		}
 
+		found = false;
+		spin_lock(&ce->guc_state.lock);
 		list_for_each_entry(rq, &ce->guc_state.requests, sched.link) {
 			if (i915_test_request_state(rq) != I915_REQUEST_ACTIVE)
 				continue;
 
+			found = true;
+			break;
+		}
+		spin_unlock(&ce->guc_state.lock);
+
+		if (found) {
 			intel_engine_set_hung_context(engine, ce);
 
 			/* Can only cope with one hang at a time... */
@@ -4847,6 +4857,7 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
 			xa_lock(&guc->context_lookup);
 			goto done;
 		}
+
 next:
 		intel_context_put(ce);
 		xa_lock(&guc->context_lookup);
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 9d5d5a397b64e..4107a0dfcca7d 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -1607,6 +1607,7 @@ capture_engine(struct intel_engine_cs *engine,
 	ce = intel_engine_get_hung_context(engine);
 	if (ce) {
 		intel_engine_clear_hung_context(engine);
+		/* This will reference count the request (if found) */
 		rq = intel_context_find_active_request(ce);
 		if (!rq || !i915_request_started(rq))
 			goto no_request_capture;
@@ -1618,13 +1619,11 @@ capture_engine(struct intel_engine_cs *engine,
 		if (!intel_uc_uses_guc_submission(&engine->gt->uc)) {
 			spin_lock_irqsave(&engine->sched_engine->lock, flags);
 			rq = intel_engine_execlist_find_hung_request(engine);
+			rq = i915_request_get_rcu(rq);
 			spin_unlock_irqrestore(&engine->sched_engine->lock,
 					       flags);
 		}
 	}
-	if (rq)
-		rq = i915_request_get_rcu(rq);
-
 	if (!rq)
 		goto no_request_capture;
 
-- 
2.39.0