From 93505ee7d05e836fd18894019e93c3875198fcc5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>
Date: Mon, 5 Aug 2019 11:14:27 +0200
Subject: dma-buf: fix busy wait for new shared fences
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Git-commit: 93505ee7d05e836fd18894019e93c3875198fcc5
Patch-mainline: v5.4-rc1
References: bsc#1152472

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/
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/dma-buf/reservation.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index c71b85c8c159..d59207ca72d2 100644
--- 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 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
 
 	write_seqcount_end(&obj->seq);
 	preempt_enable();
+	dma_fence_put(old);
 }
 EXPORT_SYMBOL(reservation_object_add_shared_fence);
 
-- 
2.28.0