drm/i915: make lockdep slightly happier about execbuf.

As soon as we install fences, we should stop allocating memory
in order to prevent any potential deadlocks.

This is required later on, when we start adding support for
dma-fence annotations.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-11-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c

@@ -50,11 +50,12 @@ enum {
 #define DBG_FORCE_RELOC 0 /* choose one of the above! */
 };
 
-#define __EXEC_OBJECT_HAS_PIN		BIT(31)
-#define __EXEC_OBJECT_HAS_FENCE		BIT(30)
-#define __EXEC_OBJECT_NEEDS_MAP		BIT(29)
-#define __EXEC_OBJECT_NEEDS_BIAS	BIT(28)
-#define __EXEC_OBJECT_INTERNAL_FLAGS	(~0u << 28) /* all of the above */
+/* __EXEC_OBJECT_NO_RESERVE is BIT(31), defined in i915_vma.h */
+#define __EXEC_OBJECT_HAS_PIN		BIT(30)
+#define __EXEC_OBJECT_HAS_FENCE		BIT(29)
+#define __EXEC_OBJECT_NEEDS_MAP		BIT(28)
+#define __EXEC_OBJECT_NEEDS_BIAS	BIT(27)
+#define __EXEC_OBJECT_INTERNAL_FLAGS	(~0u << 27) /* all of the above + */
 #define __EXEC_OBJECT_RESERVED (__EXEC_OBJECT_HAS_PIN | __EXEC_OBJECT_HAS_FENCE)
 
 #define __EXEC_HAS_RELOC	BIT(31)
@@ -935,6 +936,12 @@ static int eb_validate_vmas(struct i915_execbuffer *eb)
 			}
 		}
 
+		if (!(ev->flags & EXEC_OBJECT_WRITE)) {
+			err = dma_resv_reserve_shared(vma->resv, 1);
+			if (err)
+				return err;
+		}
+
 		GEM_BUG_ON(drm_mm_node_allocated(&vma->node) &&
 			   eb_vma_misplaced(&eb->exec[i], vma, ev->flags));
 	}
@@ -2202,7 +2209,8 @@ static int eb_move_to_gpu(struct i915_execbuffer *eb)
 		}
 
 		if (err == 0)
-			err = i915_vma_move_to_active(vma, eb->request, flags);
+			err = i915_vma_move_to_active(vma, eb->request,
+						      flags | __EXEC_OBJECT_NO_RESERVE);
 	}
 
 	if (unlikely(err))
@@ -2454,6 +2462,10 @@ static int eb_parse_pipeline(struct i915_execbuffer *eb,
 	if (err)
 		goto err_commit;
 
+	err = dma_resv_reserve_shared(shadow->resv, 1);
+	if (err)
+		goto err_commit;
+
 	/* Wait for all writes (and relocs) into the batch to complete */
 	err = i915_sw_fence_await_reservation(&pw->base.chain,
 					      pw->batch->resv, NULL, false,

drivers/gpu/drm/i915/i915_active.c

@@ -293,18 +293,13 @@ static struct active_node *__active_lookup(struct i915_active *ref, u64 idx)
 static struct i915_active_fence *
 active_instance(struct i915_active *ref, u64 idx)
 {
-	struct active_node *node, *prealloc;
+	struct active_node *node;
 	struct rb_node **p, *parent;
 
 	node = __active_lookup(ref, idx);
 	if (likely(node))
 		return &node->base;
 
-	/* Preallocate a replacement, just in case */
-	prealloc = kmem_cache_alloc(global.slab_cache, GFP_KERNEL);
-	if (!prealloc)
-		return NULL;
-
 	spin_lock_irq(&ref->tree_lock);
 	GEM_BUG_ON(i915_active_is_idle(ref));
 
@@ -314,10 +309,8 @@ active_instance(struct i915_active *ref, u64 idx)
 		parent = *p;
 
 		node = rb_entry(parent, struct active_node, node);
-		if (node->timeline == idx) {
-			kmem_cache_free(global.slab_cache, prealloc);
+		if (node->timeline == idx)
 			goto out;
-		}
 
 		if (node->timeline < idx)
 			p = &parent->rb_right;
@@ -325,7 +318,14 @@ active_instance(struct i915_active *ref, u64 idx)
 			p = &parent->rb_left;
 	}
 
-	node = prealloc;
+	/*
+	 * XXX: We should preallocate this before i915_active_ref() is ever
+	 *  called, but we cannot call into fs_reclaim() anyway, so use GFP_ATOMIC.
+	 */
+	node = kmem_cache_alloc(global.slab_cache, GFP_ATOMIC);
+	if (!node)
+		goto out;
+
 	__i915_active_fence_init(&node->base, NULL, node_retire);
 	node->ref = ref;
 	node->timeline = idx;

drivers/gpu/drm/i915/i915_vma.c

@@ -1247,9 +1247,11 @@ int i915_vma_move_to_active(struct i915_vma *vma,
 		obj->write_domain = I915_GEM_DOMAIN_RENDER;
 		obj->read_domains = 0;
 	} else {
-		err = dma_resv_reserve_shared(vma->resv, 1);
-		if (unlikely(err))
-			return err;
+		if (!(flags & __EXEC_OBJECT_NO_RESERVE)) {
+			err = dma_resv_reserve_shared(vma->resv, 1);
+			if (unlikely(err))
+				return err;
+		}
 
 		dma_resv_add_shared_fence(vma->resv, &rq->fence);
 		obj->write_domain = 0;

drivers/gpu/drm/i915/i915_vma.h

@@ -52,6 +52,9 @@ static inline bool i915_vma_is_active(const struct i915_vma *vma)
 	return !i915_active_is_idle(&vma->active);
 }
 
+/* do not reserve memory to prevent deadlocks */
+#define __EXEC_OBJECT_NO_RESERVE BIT(31)
+
 int __must_check __i915_vma_move_to_active(struct i915_vma *vma,
 					   struct i915_request *rq);
 int __must_check i915_vma_move_to_active(struct i915_vma *vma,