sync: Fix race condition between merge and signal

The copied sync_pt was activated immediately. If the sync_pt was
signaled before the entire merge was completed, the new fence's pt_list
could be iterated over while it is still in the process of being
created.

Moving the the sync_pt_activate call for all new sync_pts to after both
the sync_fence_copy_pts and the sync_fence_merge_pts calls ensure that
the pt_list is complete and immutable before it can be reached from the
timeline's active list.

Signed-off-by: Erik Gilling <konkers@android.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/drivers/base/sync.c b/drivers/base/sync.c
index 809d02b21e0..a97a503f013 100644
--- a/drivers/base/sync.c
+++ b/drivers/base/sync.c
@@ -324,7 +324,6 @@ static int sync_fence_copy_pts(struct sync_fence *dst, struct sync_fence *src)
 
                 new_pt->fence = dst;
                 list_add(&new_pt->pt_list, &dst->pt_list_head);
-                sync_pt_activate(new_pt);
         }
 
         return 0;
@@ -356,7 +355,6 @@ static int sync_fence_merge_pts(struct sync_fence *dst, struct sync_fence *src)
                                         new_pt->fence = dst;
                                         list_replace(&dst_pt->pt_list,
                                                      &new_pt->pt_list);
-                                        sync_pt_activate(new_pt);
                                         sync_pt_free(dst_pt);
                                 }
                                 collapsed = true;
@@ -372,7 +370,6 @@ static int sync_fence_merge_pts(struct sync_fence *dst, struct sync_fence *src)
 
                         new_pt->fence = dst;
                         list_add(&new_pt->pt_list, &dst->pt_list_head);
-                        sync_pt_activate(new_pt);
                 }
         }
 
@@ -453,6 +450,7 @@ struct sync_fence *sync_fence_merge(const char *name,
                                     struct sync_fence *a, struct sync_fence *b)
 {
         struct sync_fence *fence;
+        struct list_head *pos;
         int err;
 
         fence = sync_fence_alloc(name);
@@ -467,6 +465,12 @@ struct sync_fence *sync_fence_merge(const char *name,
         if (err < 0)
                 goto err;
 
+        list_for_each(pos, &fence->pt_list_head) {
+                struct sync_pt *pt =
+                        container_of(pos, struct sync_pt, pt_list);
+                sync_pt_activate(pt);
+        }
+
         /*
          * signal the fence in case one of it's pts were activated before
          * they were activated