dma-buf/sw-sync: Fix locking around sync_timeline lists

The sync_pt were not adding themselves atomically to the timeline lists,
corruption imminent.  Only a single list is required to track the
unsignaled sync_pt, so reduce it and rename the lock more appropriately
along with using idiomatic names to distinguish a list from links along
it.

v2: Prevent spinlock recursion on free during create (next patch) and
fixup crossref in kerneldoc

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170629210532.5617-1-chris@chris-wilson.co.uk

drivers/dma-buf/sw_sync.c

@@ -96,9 +96,8 @@ static struct sync_timeline *sync_timeline_create(const char *name)
 	obj->context = dma_fence_context_alloc(1);
 	strlcpy(obj->name, name, sizeof(obj->name));
 
-	INIT_LIST_HEAD(&obj->child_list_head);
-	INIT_LIST_HEAD(&obj->active_list_head);
-	spin_lock_init(&obj->child_list_lock);
+	INIT_LIST_HEAD(&obj->pt_list);
+	spin_lock_init(&obj->lock);
 
 	sync_timeline_debug_add(obj);
 
@@ -139,17 +138,15 @@ static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc)
 
 	trace_sync_timeline(obj);
 
-	spin_lock_irq(&obj->child_list_lock);
+	spin_lock_irq(&obj->lock);
 
 	obj->value += inc;
 
-	list_for_each_entry_safe(pt, next, &obj->active_list_head,
-				 active_list) {
+	list_for_each_entry_safe(pt, next, &obj->pt_list, link)
 		if (dma_fence_is_signaled_locked(&pt->base))
-			list_del_init(&pt->active_list);
-	}
+			list_del_init(&pt->link);
 
-	spin_unlock_irq(&obj->child_list_lock);
+	spin_unlock_irq(&obj->lock);
 }
 
 /**
@@ -171,15 +168,15 @@ static struct sync_pt *sync_pt_create(struct sync_timeline *obj,
 	if (!pt)
 		return NULL;
 
-	spin_lock_irq(&obj->child_list_lock);
-
 	sync_timeline_get(obj);
-	dma_fence_init(&pt->base, &timeline_fence_ops, &obj->child_list_lock,
+	dma_fence_init(&pt->base, &timeline_fence_ops, &obj->lock,
 		       obj->context, value);
-	list_add_tail(&pt->child_list, &obj->child_list_head);
-	INIT_LIST_HEAD(&pt->active_list);
+	INIT_LIST_HEAD(&pt->link);
 
-	spin_unlock_irq(&obj->child_list_lock);
+	spin_lock_irq(&obj->lock);
+	if (!dma_fence_is_signaled_locked(&pt->base))
+		list_add_tail(&pt->link, &obj->pt_list);
+	spin_unlock_irq(&obj->lock);
 
 	return pt;
 }
@@ -200,15 +197,15 @@ static void timeline_fence_release(struct dma_fence *fence)
 {
 	struct sync_pt *pt = dma_fence_to_sync_pt(fence);
 	struct sync_timeline *parent = dma_fence_parent(fence);
-	unsigned long flags;
 
-	spin_lock_irqsave(fence->lock, flags);
+	if (!list_empty(&pt->link)) {
+		unsigned long flags;
 
-	list_del(&pt->child_list);
-	if (!list_empty(&pt->active_list))
-		list_del(&pt->active_list);
-
-	spin_unlock_irqrestore(fence->lock, flags);
+		spin_lock_irqsave(fence->lock, flags);
+		if (!list_empty(&pt->link))
+			list_del(&pt->link);
+		spin_unlock_irqrestore(fence->lock, flags);
+	}
 
 	sync_timeline_put(parent);
 	dma_fence_free(fence);
@@ -223,13 +220,6 @@ static bool timeline_fence_signaled(struct dma_fence *fence)
 
 static bool timeline_fence_enable_signaling(struct dma_fence *fence)
 {
-	struct sync_pt *pt = dma_fence_to_sync_pt(fence);
-	struct sync_timeline *parent = dma_fence_parent(fence);
-
-	if (timeline_fence_signaled(fence))
-		return false;
-
-	list_add_tail(&pt->active_list, &parent->active_list_head);
 	return true;
 }
 

drivers/dma-buf/sync_debug.c

@@ -119,13 +119,12 @@ static void sync_print_obj(struct seq_file *s, struct sync_timeline *obj)
 
 	seq_printf(s, "%s: %d\n", obj->name, obj->value);
 
-	spin_lock_irq(&obj->child_list_lock);
-	list_for_each(pos, &obj->child_list_head) {
-		struct sync_pt *pt =
-			container_of(pos, struct sync_pt, child_list);
+	spin_lock_irq(&obj->lock);
+	list_for_each(pos, &obj->pt_list) {
+		struct sync_pt *pt = container_of(pos, struct sync_pt, link);
 		sync_print_fence(s, &pt->base, false);
 	}
-	spin_unlock_irq(&obj->child_list_lock);
+	spin_unlock_irq(&obj->lock);
 }
 
 static void sync_print_sync_file(struct seq_file *s,

drivers/dma-buf/sync_debug.h

@@ -24,42 +24,37 @@
  * struct sync_timeline - sync object
  * @kref:		reference count on fence.
  * @name:		name of the sync_timeline. Useful for debugging
- * @child_list_head:	list of children sync_pts for this sync_timeline
- * @child_list_lock:	lock protecting @child_list_head and fence.status
- * @active_list_head:	list of active (unsignaled/errored) sync_pts
+ * @lock:		lock protecting @pt_list and @value
+ * @pt_list:		list of active (unsignaled/errored) sync_pts
  * @sync_timeline_list:	membership in global sync_timeline_list
  */
 struct sync_timeline {
 	struct kref		kref;
 	char			name[32];
 
-	/* protected by child_list_lock */
+	/* protected by lock */
 	u64			context;
 	int			value;
 
-	struct list_head	child_list_head;
-	spinlock_t		child_list_lock;
-
-	struct list_head	active_list_head;
+	struct list_head	pt_list;
+	spinlock_t		lock;
 
 	struct list_head	sync_timeline_list;
 };
 
 static inline struct sync_timeline *dma_fence_parent(struct dma_fence *fence)
 {
-	return container_of(fence->lock, struct sync_timeline, child_list_lock);
+	return container_of(fence->lock, struct sync_timeline, lock);
 }
 
 /**
  * struct sync_pt - sync_pt object
  * @base: base fence object
- * @child_list: sync timeline child's list
- * @active_list: sync timeline active child's list
+ * @link: link on the sync timeline's list
  */
 struct sync_pt {
 	struct dma_fence base;
-	struct list_head child_list;
-	struct list_head active_list;
+	struct list_head link;
 };
 
 #ifdef CONFIG_SW_SYNC