drm/nouveau: fence: fix undefined fence state after emit

nouveau_fence_emit() can fail before and after initializing the
dma-fence and hence before and after initializing the dma-fence' kref.

In order to avoid nouveau_fence_emit() potentially failing before
dma-fence initialization pass the channel to nouveau_fence_new() already
and perform the required check before even allocating the fence.

While at it, restore the original behavior of nouveau_fence_new() and
add nouveau_fence_create() for separate (pre-)allocation instead. Always
splitting up allocation end emit wasn't a good idea in the first place.
Hence, limit it to the places where we actually need to pre-allocate.

Fixes: 7f2a0b50b2 ("drm/nouveau: fence: separate fence alloc and emit")
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230829223847.4406-1-dakr@redhat.com

drivers/gpu/drm/nouveau/dispnv04/crtc.c

@@ -1122,18 +1122,11 @@ nv04_page_flip_emit(struct nouveau_channel *chan,
 	PUSH_NVSQ(push, NV_SW, NV_SW_PAGE_FLIP, 0x00000000);
 	PUSH_KICK(push);
 
-	ret = nouveau_fence_new(pfence);
+	ret = nouveau_fence_new(pfence, chan);
 	if (ret)
 		goto fail;
 
-	ret = nouveau_fence_emit(*pfence, chan);
-	if (ret)
-		goto fail_fence_unref;
-
 	return 0;
-
-fail_fence_unref:
-	nouveau_fence_unref(pfence);
 fail:
 	spin_lock_irqsave(&dev->event_lock, flags);
 	list_del(&s->head);

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -875,16 +875,10 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object *bo, int evict,
 	if (ret)
 		goto out_unlock;
 
-	ret = nouveau_fence_new(&fence);
+	ret = nouveau_fence_new(&fence, chan);
 	if (ret)
 		goto out_unlock;
 
-	ret = nouveau_fence_emit(fence, chan);
-	if (ret) {
-		nouveau_fence_unref(&fence);
-		goto out_unlock;
-	}
-
 	/* TODO: figure out a better solution here
 	 *
 	 * wait on the fence here explicitly as going through

drivers/gpu/drm/nouveau/nouveau_chan.c

@@ -70,10 +70,8 @@ nouveau_channel_idle(struct nouveau_channel *chan)
 		struct nouveau_fence *fence = NULL;
 		int ret;
 
-		ret = nouveau_fence_new(&fence);
+		ret = nouveau_fence_new(&fence, chan);
 		if (!ret) {
-			ret = nouveau_fence_emit(fence, chan);
-			if (!ret)
 			ret = nouveau_fence_wait(fence, false, false);
 			nouveau_fence_unref(&fence);
 		}

drivers/gpu/drm/nouveau/nouveau_dmem.c

@@ -209,8 +209,7 @@ static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
 		goto done;
 	}
 
-	if (!nouveau_fence_new(&fence))
-		nouveau_fence_emit(fence, dmem->migrate.chan);
+	nouveau_fence_new(&fence, dmem->migrate.chan);
 	migrate_vma_pages(&args);
 	nouveau_dmem_fence_done(&fence);
 	dma_unmap_page(drm->dev->dev, dma_addr, PAGE_SIZE, DMA_BIDIRECTIONAL);
@@ -403,8 +402,7 @@ nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk)
 		}
 	}
 
-	if (!nouveau_fence_new(&fence))
-		nouveau_fence_emit(fence, chunk->drm->dmem->migrate.chan);
+	nouveau_fence_new(&fence, chunk->drm->dmem->migrate.chan);
 	migrate_device_pages(src_pfns, dst_pfns, npages);
 	nouveau_dmem_fence_done(&fence);
 	migrate_device_finalize(src_pfns, dst_pfns, npages);
@@ -677,8 +675,7 @@ static void nouveau_dmem_migrate_chunk(struct nouveau_drm *drm,
 		addr += PAGE_SIZE;
 	}
 
-	if (!nouveau_fence_new(&fence))
-		nouveau_fence_emit(fence, drm->dmem->migrate.chan);
+	nouveau_fence_new(&fence, drm->dmem->migrate.chan);
 	migrate_vma_pages(args);
 	nouveau_dmem_fence_done(&fence);
 	nouveau_pfns_map(svmm, args->vma->vm_mm, args->start, pfns, i);

drivers/gpu/drm/nouveau/nouveau_exec.c

@@ -96,7 +96,8 @@ nouveau_exec_job_submit(struct nouveau_job *job)
 	unsigned long index;
 	int ret;
 
-	ret = nouveau_fence_new(&exec_job->fence);
+	/* Create a new fence, but do not emit yet. */
+	ret = nouveau_fence_create(&exec_job->fence, exec_job->chan);
 	if (ret)
 		return ret;
 
@@ -170,13 +171,17 @@ nouveau_exec_job_run(struct nouveau_job *job)
 		nv50_dma_push(chan, p->va, p->va_len, no_prefetch);
 	}
 
-	ret = nouveau_fence_emit(fence, chan);
+	ret = nouveau_fence_emit(fence);
 	if (ret) {
+		nouveau_fence_unref(&exec_job->fence);
 		NV_PRINTK(err, job->cli, "error fencing pushbuf: %d\n", ret);
 		WIND_RING(chan);
 		return ERR_PTR(ret);
 	}
 
+	/* The fence was emitted successfully, set the job's fence pointer to
+	 * NULL in order to avoid freeing it up when the job is cleaned up.
+	 */
 	exec_job->fence = NULL;
 
 	return &fence->base;
@@ -189,7 +194,7 @@ nouveau_exec_job_free(struct nouveau_job *job)
 
 	nouveau_job_free(job);
 
-	nouveau_fence_unref(&exec_job->fence);
+	kfree(exec_job->fence);
 	kfree(exec_job->push.s);
 	kfree(exec_job);
 }

drivers/gpu/drm/nouveau/nouveau_fence.c

@@ -205,16 +205,13 @@ nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_cha
 }
 
 int
-nouveau_fence_emit(struct nouveau_fence *fence, struct nouveau_channel *chan)
+nouveau_fence_emit(struct nouveau_fence *fence)
 {
+	struct nouveau_channel *chan = fence->channel;
 	struct nouveau_fence_chan *fctx = chan->fence;
 	struct nouveau_fence_priv *priv = (void*)chan->drm->fence;
 	int ret;
 
-	if (unlikely(!chan->fence))
-		return -ENODEV;
-
-	fence->channel  = chan;
 	fence->timeout  = jiffies + (15 * HZ);
 
 	if (priv->uevent)
@@ -406,18 +403,41 @@ nouveau_fence_unref(struct nouveau_fence **pfence)
 }
 
 int
-nouveau_fence_new(struct nouveau_fence **pfence)
+nouveau_fence_create(struct nouveau_fence **pfence,
+		     struct nouveau_channel *chan)
 {
 	struct nouveau_fence *fence;
 
+	if (unlikely(!chan->fence))
+		return -ENODEV;
+
 	fence = kzalloc(sizeof(*fence), GFP_KERNEL);
 	if (!fence)
 		return -ENOMEM;
 
+	fence->channel = chan;
+
 	*pfence = fence;
 	return 0;
 }
 
+int
+nouveau_fence_new(struct nouveau_fence **pfence,
+		  struct nouveau_channel *chan)
+{
+	int ret = 0;
+
+	ret = nouveau_fence_create(pfence, chan);
+	if (ret)
+		return ret;
+
+	ret = nouveau_fence_emit(*pfence);
+	if (ret)
+		nouveau_fence_unref(pfence);
+
+	return ret;
+}
+
 static const char *nouveau_fence_get_get_driver_name(struct dma_fence *fence)
 {
 	return "nouveau";

drivers/gpu/drm/nouveau/nouveau_fence.h

@@ -17,10 +17,11 @@ struct nouveau_fence {
 	unsigned long timeout;
 };
 
-int  nouveau_fence_new(struct nouveau_fence **);
+int  nouveau_fence_create(struct nouveau_fence **, struct nouveau_channel *);
+int  nouveau_fence_new(struct nouveau_fence **, struct nouveau_channel *);
 void nouveau_fence_unref(struct nouveau_fence **);
 
-int  nouveau_fence_emit(struct nouveau_fence *, struct nouveau_channel *);
+int  nouveau_fence_emit(struct nouveau_fence *);
 bool nouveau_fence_done(struct nouveau_fence *);
 int  nouveau_fence_wait(struct nouveau_fence *, bool lazy, bool intr);
 int  nouveau_fence_sync(struct nouveau_bo *, struct nouveau_channel *, bool exclusive, bool intr);

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -914,11 +914,8 @@ revalidate:
 		}
 	}
 
-	ret = nouveau_fence_new(&fence);
-	if (!ret)
-		ret = nouveau_fence_emit(fence, chan);
+	ret = nouveau_fence_new(&fence, chan);
 	if (ret) {
-		nouveau_fence_unref(&fence);
 		NV_PRINTK(err, cli, "error fencing pushbuf: %d\n", ret);
 		WIND_RING(chan);
 		goto out;