dma-buf: fix busy wait for new shared fences

When reservation_object_add_shared_fence is replacing an old fence with a new
one we should not drop the old one before the new one is in place.

Otherwise other cores can busy wait for the new one to appear.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/322030/

diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index c71b85c8c159292845ee0c1fb33441c00cb46144..d59207ca72d2e386b179d157d10e79afa48b973a 100644 (file)
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -196,6 +196,7 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
                                         struct dma_fence *fence)
 {
        struct reservation_object_list *fobj;
+       struct dma_fence *old;
        unsigned int i, count;
 
        dma_fence_get(fence);
@@ -209,18 +210,16 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
        write_seqcount_begin(&obj->seq);
 
        for (i = 0; i < count; ++i) {
-               struct dma_fence *old_fence;
 
-               old_fence = rcu_dereference_protected(fobj->shared[i],
-                                                     reservation_object_held(obj));
-               if (old_fence->context == fence->context ||
-                   dma_fence_is_signaled(old_fence)) {
-                       dma_fence_put(old_fence);
+               old = rcu_dereference_protected(fobj->shared[i],
+                                               reservation_object_held(obj));
+               if (old->context == fence->context ||
+                   dma_fence_is_signaled(old))
                        goto replace;
-               }
        }
 
        BUG_ON(fobj->shared_count >= fobj->shared_max);
+       old = NULL;
        count++;
 
 replace:
@@ -230,6 +229,7 @@ replace:
 
        write_seqcount_end(&obj->seq);
        preempt_enable();
+       dma_fence_put(old);
 }
 EXPORT_SYMBOL(reservation_object_add_shared_fence);