[PATCH] dma-buf/reservation: should keep later one in add fence(v3)

[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.Liu at 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();
-- 
2.7.4