[PATCH v4 5/5] drm/i915/gt: Make sure that errors are propagated through request chains

[Andi Shyti]

Currently, when we perform operations such as clearing or copying
large blocks of memory, we generate multiple requests that are
executed in a chain.

However, if one of these requests fails, we may not realize it
unless it happens to be the last request in the chain. This is
because errors are not properly propagated.

For this we need to keep propagating the chain of fence
notification in order to always reach the final fence associated
to the final request.

To address this issue, we need to ensure that the chain of fence
notifications is always propagated so that we can reach the final
fence associated with the last request. By doing so, we will be
able to detect any memory operation  failures and determine
whether the memory is still invalid.

On copy and clear migration signal fences upon completion.

On copy and clear migration, signal fences upon request
completion to ensure that we have a reliable perpetuation of the
operation outcome.

Fixes: cf586021642d80 ("drm/i915/gt: Pipelined page migration")
Reported-by: Matthew Auld <matthew.auld at intel.com>
Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Andi Shyti <andi.shyti at linux.intel.com>
Cc: stable at vger.kernel.org
Reviewed-by: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_migrate.c | 41 ++++++++++++++++++-------
 1 file changed, 30 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_migrate.c b/drivers/gpu/drm/i915/gt/intel_migrate.c
index 3f638f1987968..0031e7b1b4704 100644
--- a/drivers/gpu/drm/i915/gt/intel_migrate.c
+++ b/drivers/gpu/drm/i915/gt/intel_migrate.c
@@ -742,13 +742,19 @@ intel_context_migrate_copy(struct intel_context *ce,
 			dst_offset = 2 * CHUNK_SZ;
 	}
 
+	/*
+	 * While building the chain of requests, we need to ensure
+	 * that no one can sneak into the timeline unnoticed.
+	 */
+	mutex_lock(&ce->timeline->mutex);
+
 	do {
 		int len;
 
-		rq = i915_request_create(ce);
+		rq = i915_request_create_locked(ce);
 		if (IS_ERR(rq)) {
 			err = PTR_ERR(rq);
-			goto out_ce;
+			break;
 		}
 
 		if (deps) {
@@ -878,10 +884,14 @@ intel_context_migrate_copy(struct intel_context *ce,
 
 		/* Arbitration is re-enabled between requests. */
 out_rq:
-		if (*out)
+		i915_sw_fence_await(&rq->submit);
+		i915_request_get(rq);
+		i915_request_add_locked(rq);
+		if (*out) {
+			i915_sw_fence_complete(&(*out)->submit);
 			i915_request_put(*out);
-		*out = i915_request_get(rq);
-		i915_request_add(rq);
+		}
+		*out = rq;
 
 		if (err)
 			break;
@@ -905,7 +915,10 @@ intel_context_migrate_copy(struct intel_context *ce,
 		cond_resched();
 	} while (1);
 
-out_ce:
+	mutex_unlock(&ce->timeline->mutex);
+
+	if (*out)
+		i915_sw_fence_complete(&(*out)->submit);
 	return err;
 }
 
@@ -1005,7 +1018,7 @@ intel_context_migrate_clear(struct intel_context *ce,
 		rq = i915_request_create(ce);
 		if (IS_ERR(rq)) {
 			err = PTR_ERR(rq);
-			goto out_ce;
+			break;
 		}
 
 		if (deps) {
@@ -1056,17 +1069,23 @@ intel_context_migrate_clear(struct intel_context *ce,
 
 		/* Arbitration is re-enabled between requests. */
 out_rq:
-		if (*out)
-			i915_request_put(*out);
-		*out = i915_request_get(rq);
+		i915_sw_fence_await(&rq->submit);
+		i915_request_get(rq);
 		i915_request_add(rq);
+		if (*out) {
+			i915_sw_fence_complete(&(*out)->submit);
+			i915_request_put(*out);
+		}
+		*out = rq;
+
 		if (err || !it.sg || !sg_dma_len(it.sg))
 			break;
 
 		cond_resched();
 	} while (1);
 
-out_ce:
+	if (*out)
+		i915_sw_fence_complete(&(*out)->submit);
 	return err;
 }
 
-- 
2.39.2