drm/nouveau/fence/g84-: protect against concurrent access to semaphore buffers

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_fence.h

@@ -99,6 +99,7 @@ struct nv84_fence_priv {
 	struct nouveau_bo *bo;
 	struct nouveau_bo *bo_gart;
 	u32 *suspend;
+	struct mutex mutex;
 };
 
 int  nv84_fence_context_new(struct nouveau_channel *);

drivers/gpu/drm/nouveau/nv84_fence.c

@@ -107,8 +107,10 @@ nv84_fence_context_del(struct nouveau_channel *chan)
 	struct nv84_fence_chan *fctx = chan->fence;
 
 	nouveau_bo_wr32(priv->bo, chan->chid * 16 / 4, fctx->base.sequence);
+	mutex_lock(&priv->mutex);
 	nouveau_bo_vma_del(priv->bo, &fctx->vma_gart);
 	nouveau_bo_vma_del(priv->bo, &fctx->vma);
+	mutex_unlock(&priv->mutex);
 	nouveau_fence_context_del(&fctx->base);
 	chan->fence = NULL;
 	nouveau_fence_context_free(&fctx->base);
@@ -134,11 +136,13 @@ nv84_fence_context_new(struct nouveau_channel *chan)
 	fctx->base.sync32 = nv84_fence_sync32;
 	fctx->base.sequence = nv84_fence_read(chan);
 
+	mutex_lock(&priv->mutex);
 	ret = nouveau_bo_vma_add(priv->bo, cli->vm, &fctx->vma);
 	if (ret == 0) {
 		ret = nouveau_bo_vma_add(priv->bo_gart, cli->vm,
 					&fctx->vma_gart);
 	}
+	mutex_unlock(&priv->mutex);
 
 	if (ret)
 		nv84_fence_context_del(chan);
@@ -212,6 +216,8 @@ nv84_fence_create(struct nouveau_drm *drm)
 	priv->base.context_base = dma_fence_context_alloc(priv->base.contexts);
 	priv->base.uevent = true;
 
+	mutex_init(&priv->mutex);
+
 	/* Use VRAM if there is any ; otherwise fallback to system memory */
 	domain = drm->device.info.ram_size != 0 ? TTM_PL_FLAG_VRAM :
 			 /*