Re: [PATCH 21/27] drm/i915/guc: Proper xarray usage for contexts_lookup

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On 8/25/2021 5:41 PM, Matthew Brost wrote:
On Wed, Aug 25, 2021 at 05:44:11PM -0700, Daniele Ceraolo Spurio wrote:

On 8/18/2021 11:16 PM, Matthew Brost wrote:
Lock the xarray and take ref to the context if needed.

v2:
   (Checkpatch)
    - Add new line after declaration
   (Daniel Vetter)
    - Correct put / get accounting in xa_for_loops

Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
---
   .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 103 +++++++++++++++---
   1 file changed, 88 insertions(+), 15 deletions(-)

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 509b298e7cf3..5f77f25322ca 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -606,8 +606,18 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
   	unsigned long index, flags;
   	bool pending_disable, pending_enable, deregister, destroyed, banned;
+	xa_lock_irqsave(&guc->context_lookup, flags);
   	xa_for_each(&guc->context_lookup, index, ce) {
-		spin_lock_irqsave(&ce->guc_state.lock, flags);
+		/*
+		 * Corner case where the ref count on the object is zero but and
+		 * deregister G2H was lost. In this case we don't touch the ref
+		 * count and finish the destroy of the context.
+		 */
+		bool do_put = kref_get_unless_zero(&ce->ref);
+
+		xa_unlock(&guc->context_lookup);
+
+		spin_lock(&ce->guc_state.lock);
   		/*
   		 * Once we are at this point submission_disabled() is guaranteed
@@ -623,7 +633,9 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
   		banned = context_banned(ce);
   		init_sched_state(ce);
-		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
+		spin_unlock(&ce->guc_state.lock);
+
+		GEM_BUG_ON(!do_put && !destroyed);
   		if (pending_enable || destroyed || deregister) {
   			decr_outstanding_submission_g2h(guc);
@@ -646,13 +658,19 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
   			}
   			intel_context_sched_disable_unpin(ce);
   			decr_outstanding_submission_g2h(guc);
-			spin_lock_irqsave(&ce->guc_state.lock, flags);
+
+			spin_lock(&ce->guc_state.lock);
   			guc_blocked_fence_complete(ce);
-			spin_unlock_irqrestore(&ce->guc_state.lock, flags);
+			spin_unlock(&ce->guc_state.lock);
   			intel_context_put(ce);
   		}
+
+		if (do_put)
+			intel_context_put(ce);
is it safe to do the put outside the xa_lock, in case the refcount goes to
zero with this? I know it is unlikely because the refcount was > 0 if do_put
is true, but it might've gone down between us checking earlier and now.

It is safe as xa_for_each indicates it is safe to destroy / delete
objects from the array while traversing it.

ok.

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>

Daniele

+		xa_lock(&guc->context_lookup);
   	}
+	xa_unlock_irqrestore(&guc->context_lookup, flags);
   }
   static inline bool
@@ -873,16 +891,29 @@ void intel_guc_submission_reset(struct intel_guc *guc, bool stalled)
   {
   	struct intel_context *ce;
   	unsigned long index;
+	unsigned long flags;
   	if (unlikely(!guc_submission_initialized(guc))) {
   		/* Reset called during driver load? GuC not yet initialised! */
   		return;
   	}
-	xa_for_each(&guc->context_lookup, index, ce)
+	xa_lock_irqsave(&guc->context_lookup, flags);
+	xa_for_each(&guc->context_lookup, index, ce) {
+		if (!kref_get_unless_zero(&ce->ref))
+			continue;
+
+		xa_unlock(&guc->context_lookup);
+
   		if (intel_context_is_pinned(ce))
   			__guc_reset_context(ce, stalled);
+		intel_context_put(ce);
+
+		xa_lock(&guc->context_lookup);
+	}
+	xa_unlock_irqrestore(&guc->context_lookup, flags);
+
   	/* GuC is blown away, drop all references to contexts */
   	xa_destroy(&guc->context_lookup);
   }
@@ -957,11 +988,24 @@ void intel_guc_submission_cancel_requests(struct intel_guc *guc)
   {
   	struct intel_context *ce;
   	unsigned long index;
+	unsigned long flags;
+
+	xa_lock_irqsave(&guc->context_lookup, flags);
+	xa_for_each(&guc->context_lookup, index, ce) {
+		if (!kref_get_unless_zero(&ce->ref))
+			continue;
+
+		xa_unlock(&guc->context_lookup);
-	xa_for_each(&guc->context_lookup, index, ce)
   		if (intel_context_is_pinned(ce))
   			guc_cancel_context_requests(ce);
+		intel_context_put(ce);
+
+		xa_lock(&guc->context_lookup);
+	}
+	xa_unlock_irqrestore(&guc->context_lookup, flags);
+
   	guc_cancel_sched_engine_requests(guc->sched_engine);
   	/* GuC is blown away, drop all references to contexts */
@@ -2850,21 +2894,28 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
   	struct intel_context *ce;
   	struct i915_request *rq;
   	unsigned long index;
+	unsigned long flags;
   	/* Reset called during driver load? GuC not yet initialised! */
   	if (unlikely(!guc_submission_initialized(guc)))
   		return;
+	xa_lock_irqsave(&guc->context_lookup, flags);
   	xa_for_each(&guc->context_lookup, index, ce) {
-		if (!intel_context_is_pinned(ce))
+		if (!kref_get_unless_zero(&ce->ref))
   			continue;
+		xa_unlock(&guc->context_lookup);
+
+		if (!intel_context_is_pinned(ce))
+			goto next;
+
   		if (intel_engine_is_virtual(ce->engine)) {
   			if (!(ce->engine->mask & engine->mask))
-				continue;
+				goto next;
   		} else {
   			if (ce->engine != engine)
-				continue;
+				goto next;
   		}
   		list_for_each_entry(rq, &ce->guc_active.requests, sched.link) {
@@ -2874,9 +2925,17 @@ void intel_guc_find_hung_context(struct intel_engine_cs *engine)
   			intel_engine_set_hung_context(engine, ce);
   			/* Can only cope with one hang at a time... */
-			return;
+			intel_context_put(ce);
+			xa_lock(&guc->context_lookup);
+			goto done;
   		}
+next:
+		intel_context_put(ce);
+		xa_lock(&guc->context_lookup);
+
nit: extra newline

Checkpatch got that one too. Already fixed.

Matt

Daniele

   	}
+done:
+	xa_unlock_irqrestore(&guc->context_lookup, flags);
   }
   void intel_guc_dump_active_requests(struct intel_engine_cs *engine,
@@ -2892,23 +2951,34 @@ void intel_guc_dump_active_requests(struct intel_engine_cs *engine,
   	if (unlikely(!guc_submission_initialized(guc)))
   		return;
+	xa_lock_irqsave(&guc->context_lookup, flags);
   	xa_for_each(&guc->context_lookup, index, ce) {
-		if (!intel_context_is_pinned(ce))
+		if (!kref_get_unless_zero(&ce->ref))
   			continue;
+		xa_unlock(&guc->context_lookup);
+
+		if (!intel_context_is_pinned(ce))
+			goto next;
+
   		if (intel_engine_is_virtual(ce->engine)) {
   			if (!(ce->engine->mask & engine->mask))
-				continue;
+				goto next;
   		} else {
   			if (ce->engine != engine)
-				continue;
+				goto next;
   		}
-		spin_lock_irqsave(&ce->guc_active.lock, flags);
+		spin_lock(&ce->guc_active.lock);
   		intel_engine_dump_active_requests(&ce->guc_active.requests,
   						  hung_rq, m);
-		spin_unlock_irqrestore(&ce->guc_active.lock, flags);
+		spin_unlock(&ce->guc_active.lock);
+
+next:
+		intel_context_put(ce);
+		xa_lock(&guc->context_lookup);
   	}
+	xa_unlock_irqrestore(&guc->context_lookup, flags);
   }
   void intel_guc_submission_print_info(struct intel_guc *guc,
@@ -2962,7 +3032,9 @@ void intel_guc_submission_print_context_info(struct intel_guc *guc,
   {
   	struct intel_context *ce;
   	unsigned long index;
+	unsigned long flags;
+	xa_lock_irqsave(&guc->context_lookup, flags);
   	xa_for_each(&guc->context_lookup, index, ce) {
   		drm_printf(p, "GuC lrc descriptor %u:\n", ce->guc_id);
   		drm_printf(p, "\tHW Context Desc: 0x%08x\n", ce->lrc.lrca);
@@ -2981,6 +3053,7 @@ void intel_guc_submission_print_context_info(struct intel_guc *guc,
   		guc_log_context_priority(p, ce);
   	}
+	xa_unlock_irqrestore(&guc->context_lookup, flags);
   }
   static struct intel_context *




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