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

3 files changed, 31 insertions, 47 deletions

diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
index 6effa1ce010e..f20d18c421a3 100644
--- a/drivers/dma-buf/sw_sync.c
+++ b/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;
 }
 
diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c
index 0e91632248ba..2264a075f6a9 100644
--- a/drivers/dma-buf/sync_debug.c
+++ b/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,
diff --git a/drivers/dma-buf/sync_debug.h b/drivers/dma-buf/sync_debug.h
index 26fe8b9907b3..6a2a8e69a7d0 100644
--- a/drivers/dma-buf/sync_debug.h
+++ b/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