[PATCH 3/8] drm/i915: Cope with request list state change during error state capture

[Tomas Elf <tomas.elf@intel.com>]

Since we're not synchronizing the ring request list during error state capture
the request list state might change between the time the corresponding error
request list was allocated and dimensioned to the time when the ring request
list is actually captured into the error state. If this happens, throw a
WARNING and do early exit and be aware that the captured error state might not
be fully reliable.

Signed-off-by: Tomas Elf <tomas.elf@intel.com>
---
 drivers/gpu/drm/i915/i915_gpu_error.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 32c1799..cc75ca4 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -1071,6 +1071,19 @@ static void i915_gem_record_rings(struct drm_device *dev,
 		list_for_each_entry_safe(request, tmpreq, &ring->request_list, list) {
 			struct drm_i915_error_request *erq;
 
+			if (WARN_ON(!request || count >= error->ring[i].num_requests)) {
+				/*
+				 * If the ring request list was changed in
+				 * between the point where the error request
+				 * list was created and dimensioned and this
+				 * point then just update the num_requests
+				 * field to reflect this.
+				 */
+				error->ring[i].num_requests =
+					min(count, error->ring[i].num_requests);
+				break;
+			}
+
 			erq = &error->ring[i].requests[count++];
 			erq->seqno = request->seqno;
 			erq->jiffies = request->emitted_jiffies;
-- 
1.9.1

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