[PATCH] drm/xe: Fix oops in xe_gem_fault when running core_hotunplug test.

[Maarten Lankhorst]

I saw an oops in xe_gem_fault when running the xe-fast-feedback
testlist against the realtime kernel without debug options enabled.

The panic happens after core_hotunplug unbind-rebind finishes.
Presumably what happens is that a process mmaps, unlocks because
of the FAULT_FLAG_RETRY_NOWAIT logic, has no process memory left,
causing ttm_bo_vm_dummy_page() to return VM_FAULT_NOPAGE, since
there was nothing left to populate, and then oopses in
"mem_type_is_vram(tbo->resource->mem_type)" because tbo->resource
is NULL.

It's convoluted, but fits the data and explains the oops after
the test exits.

Signed-off-by: Maarten Lankhorst <dev at lankhorst.se>
---
 drivers/gpu/drm/xe/xe_bo.c | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index c5a5154e1363b..68aefb6f23cde 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -1716,22 +1716,26 @@ static vm_fault_t xe_gem_fault(struct vm_fault *vmf)
 		ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
 					       TTM_BO_VM_NUM_PREFAULT);
 		drm_dev_exit(idx);
+
+		if (ret == VM_FAULT_RETRY &&
+		    !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
+			goto out;
+
+		/*
+		 * ttm_bo_vm_reserve() already has dma_resv_lock.
+		 */
+		if (ret == VM_FAULT_NOPAGE &&
+		    mem_type_is_vram(tbo->resource->mem_type)) {
+			mutex_lock(&xe->mem_access.vram_userfault.lock);
+			if (list_empty(&bo->vram_userfault_link))
+				list_add(&bo->vram_userfault_link,
+					 &xe->mem_access.vram_userfault.list);
+			mutex_unlock(&xe->mem_access.vram_userfault.lock);
+		}
 	} else {
 		ret = ttm_bo_vm_dummy_page(vmf, vmf->vma->vm_page_prot);
 	}
 
-	if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
-		goto out;
-	/*
-	 * ttm_bo_vm_reserve() already has dma_resv_lock.
-	 */
-	if (ret == VM_FAULT_NOPAGE && mem_type_is_vram(tbo->resource->mem_type)) {
-		mutex_lock(&xe->mem_access.vram_userfault.lock);
-		if (list_empty(&bo->vram_userfault_link))
-			list_add(&bo->vram_userfault_link, &xe->mem_access.vram_userfault.list);
-		mutex_unlock(&xe->mem_access.vram_userfault.lock);
-	}
-
 	dma_resv_unlock(tbo->base.resv);
 out:
 	if (needs_rpm)
-- 
2.45.2