[PATCH 2/4] drm/i915: Use a request signal pin using capture

[Thomas Hellström]

Block the request from signaling under us while capturing associated
buffer memory.

While doing so, it also becomes very apparent that the capture code
sits in the dma_fence signaling critical path, so change the GFP
mode accordingly to avoid deadlocks. That kills the lockdep splat
that was introduced with the signal pin usage.

Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gpu_error.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 2a2d7643b551..b10cdbafedfb 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -49,7 +49,7 @@
 #include "i915_memcpy.h"
 #include "i915_scatterlist.h"
 
-#define ALLOW_FAIL (GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN)
+#define ALLOW_FAIL (GFP_NOWAIT | __GFP_RETRY_MAYFAIL | __GFP_NOWARN)
 #define ATOMIC_MAYFAIL (GFP_ATOMIC | __GFP_NOWARN)
 
 static void __sg_set_buf(struct scatterlist *sg,
@@ -1462,6 +1462,7 @@ capture_engine(struct intel_engine_cs *engine,
 	struct intel_context *ce;
 	struct i915_request *rq = NULL;
 	unsigned long flags;
+	bool cookie;
 
 	ee = intel_engine_coredump_alloc(engine, GFP_KERNEL);
 	if (!ee)
@@ -1485,18 +1486,31 @@ capture_engine(struct intel_engine_cs *engine,
 					       flags);
 		}
 	}
+
+	if (rq && !i915_request_signal_pin(rq, &cookie)) {
+		rq = NULL;
+		goto no_request_capture;
+	}
+
 	if (rq)
 		capture = intel_engine_coredump_add_request(ee, rq,
 							    ATOMIC_MAYFAIL);
 	if (!capture) {
-no_request_capture:
-		kfree(ee);
-		return NULL;
+		if (rq)
+			i915_request_signal_unpin(rq, cookie);
+		goto no_request_capture;
 	}
 
 	intel_engine_coredump_add_vma(ee, capture, compress);
 
+	GEM_BUG_ON(rq && i915_request_signaled(rq));
+	i915_request_signal_unpin(rq, cookie);
+
 	return ee;
+
+no_request_capture:
+	kfree(ee);
+	return NULL;
 }
 
 static void
-- 
2.31.1