And still a NAK, the prerequisite for adding a shared fence is that it is later than any existing fence in that context.

In other words reservation_object_add_shared_fence() is always called with a new fence, never with some old one.

So the whole checking here is completely superfluous,
Christian.

Am 06.03.2018 um 08:00 schrieb Monk Liu:
v2:
still check context first to avoid warning from dma_fence_is_later
apply this fix in add_shared_replace as well

v3:
use a bool falg to indict if fence is need to insert to new slot
and ignore it if it is an eld fence compared with the one with
the same context in old->shared

Change-Id: If6a979ba9fd6c923b82212f35f07a9ff31c86767
Signed-off-by: Monk Liu <monk....@amd.com>
---
  drivers/dma-buf/reservation.c | 28 ++++++++++++++++++++++------
  1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 314eb10..a7d0598 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -118,7 +118,8 @@ reservation_object_add_shared_inplace(struct 
reservation_object *obj,
                old_fence = rcu_dereference_protected(fobj->shared[i],
                                                reservation_object_held(obj));
- if (old_fence->context == fence->context) {
+               if (old_fence->context == fence->context &&
+                       dma_fence_is_later(fence, old_fence)) {
                        /* memory barrier is added by write_seqcount_begin */
                        RCU_INIT_POINTER(fobj->shared[i], fence);
                        write_seqcount_end(&obj->seq);
@@ -158,6 +159,7 @@ reservation_object_add_shared_replace(struct 
reservation_object *obj,
                                      struct dma_fence *fence)
  {
        unsigned i, j, k;
+       bool wrong_fence = false;
dma_fence_get(fence); @@ -179,15 +181,29 @@ reservation_object_add_shared_replace(struct reservation_object *obj,
                check = rcu_dereference_protected(old->shared[i],
                                                reservation_object_held(obj));
- if (check->context == fence->context ||
-                   dma_fence_is_signaled(check))
+               if (dma_fence_is_signaled(check)) {
+                       /* put check to tail of fobj if signaled */
                        RCU_INIT_POINTER(fobj->shared[--k], check);
-               else
+               } else if (check->context == fence->context) {
+                       if (dma_fence_is_later(fence, check)) {
+                               /* put check to tail of fobj if it is 
deprecated */
+                               RCU_INIT_POINTER(fobj->shared[--k], check);
+                       } else {
+                               /* this is a wrong operation that add an eld 
fence */
+                               wrong_fence = true;
+                               RCU_INIT_POINTER(fobj->shared[j++], check);
+                       }
+               } else {
+                       /* add fence to new slot */
                        RCU_INIT_POINTER(fobj->shared[j++], check);
+               }
        }
+
        fobj->shared_count = j;
-       RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence);
-       fobj->shared_count++;
+       if (!wrong_fence) {
+               RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence);
+               fobj->shared_count++;
+       }
done:
        preempt_disable();

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