[PATCH 92/95] drm/amdgpu: Handle concurrent UALINK handle import race

[Alex Deucher <alexander.deucher@amd.com>]

From: Mukul Joshi <mukul.joshi@amd.com>

When two threads import the same UALINK handle concurrently, the first
xa_insert() succeeds and the second gets -EBUSY. Convert -EBUSY to
-EAGAIN so user-space retries instead of seeing a spurious error.

Signed-off-by: Mukul Joshi <mukul.joshi@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
index 765105aea09e2..444b0e29ee9f4 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ualink.c
@@ -3807,9 +3807,15 @@ int amdgpu_ualink_import_handle(struct drm_device *dev,
 			      imp_xa_node, GFP_KERNEL);
 		if (r) {
 			kfree(imp_xa_node);
-			dev_err(adev->dev,
-				"IMPORT: XA insert failed for handle:%llx:%llx err:%d\n",
-				handle.handle_hi, handle.handle_lo, r);
+			/* -EBUSY means another thread raced us and inserted a
+			 * node for the same handle. Ask user-space to retry.
+			 */
+			if (r == -EBUSY)
+				r = -EAGAIN;
+			else
+				dev_err(adev->dev,
+					"IMPORT: XA insert failed for handle:%llx:%llx err:%d\n",
+					handle.handle_hi, handle.handle_lo, r);
 			goto out;
 		}
 
-- 
2.55.0