[PATCH] drm/amdgpu: Fix potential race processing vm->freed

[Rob Clark <robdclark@gmail.com>]

From: Rob Clark <robdclark@chromium.org>

If userspace calls the AMDGPU_CS ioctl from multiple threads, because
the vm is global to the drm_file, you can end up with multiple threads
racing in amdgpu_vm_clear_freed().  So the freed list should be
protected with the status_lock, similar to other vm lists.

Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
Signed-off-by: Rob Clark <robdclark@chromium.org>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 33 ++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index b9441ab457ea..aeed7bc1512f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -1240,10 +1240,19 @@ int amdgpu_vm_clear_freed(struct amdgpu_device *adev,
 	struct amdgpu_bo_va_mapping *mapping;
 	uint64_t init_pte_value = 0;
 	struct dma_fence *f = NULL;
+	struct list_head freed;
 	int r;
 
-	while (!list_empty(&vm->freed)) {
-		mapping = list_first_entry(&vm->freed,
+	/*
+	 * Move the contents of the VM's freed list to a local list
+	 * that we can iterate without racing against other threads:
+	 */
+	spin_lock(&vm->status_lock);
+	list_replace_init(&vm->freed, &freed);
+	spin_unlock(&vm->status_lock);
+
+	while (!list_empty(&freed)) {
+		mapping = list_first_entry(&freed,
 			struct amdgpu_bo_va_mapping, list);
 		list_del(&mapping->list);
 
@@ -1258,6 +1267,15 @@ int amdgpu_vm_clear_freed(struct amdgpu_device *adev,
 		amdgpu_vm_free_mapping(adev, vm, mapping, f);
 		if (r) {
 			dma_fence_put(f);
+
+			/*
+			 * Move any unprocessed mappings back to the freed
+			 * list:
+			 */
+			spin_lock(&vm->status_lock);
+			list_splice_tail(&freed, &vm->freed);
+			spin_unlock(&vm->status_lock);
+
 			return r;
 		}
 	}
@@ -1583,11 +1601,14 @@ int amdgpu_vm_bo_unmap(struct amdgpu_device *adev,
 	mapping->bo_va = NULL;
 	trace_amdgpu_vm_bo_unmap(bo_va, mapping);
 
-	if (valid)
+	if (valid) {
+		spin_lock(&vm->status_lock);
 		list_add(&mapping->list, &vm->freed);
-	else
+		spin_unlock(&vm->status_lock);
+	} else {
 		amdgpu_vm_free_mapping(adev, vm, mapping,
 				       bo_va->last_pt_update);
+	}
 
 	return 0;
 }
@@ -1671,7 +1692,9 @@ int amdgpu_vm_bo_clear_mappings(struct amdgpu_device *adev,
 		    tmp->last = eaddr;
 
 		tmp->bo_va = NULL;
+		spin_lock(&vm->status_lock);
 		list_add(&tmp->list, &vm->freed);
+		spin_unlock(&vm->status_lock);
 		trace_amdgpu_vm_bo_unmap(NULL, tmp);
 	}
 
@@ -1788,7 +1811,9 @@ void amdgpu_vm_bo_del(struct amdgpu_device *adev,
 		amdgpu_vm_it_remove(mapping, &vm->va);
 		mapping->bo_va = NULL;
 		trace_amdgpu_vm_bo_unmap(bo_va, mapping);
+		spin_lock(&vm->status_lock);
 		list_add(&mapping->list, &vm->freed);
+		spin_unlock(&vm->status_lock);
 	}
 	list_for_each_entry_safe(mapping, next, &bo_va->invalids, list) {
 		list_del(&mapping->list);
-- 
2.38.1