From 0e2f733addbf7702065cc18d38b67a1284d0c2be Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>
Date: Wed, 7 Aug 2019 12:31:48 +0200
Subject: dma-buf: make dma_fence structure a bit smaller v2
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Git-commit: 0e2f733addbf7702065cc18d38b67a1284d0c2be
Patch-mainline: v5.4-rc1
References: bsc#1152472

We clear the callback list on kref_put so that by the time we
release the fence it is unused. No one should be adding to the cb_list
that they don't themselves hold a reference for.

This small change is actually making the structure 16% smaller.

v2: add the comment to the code as well.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/322916/
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 include/linux/dma-fence.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 05d29dbc7e62..bea1d05cf51e 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -65,8 +65,14 @@ struct dma_fence_cb;
 struct dma_fence {
 	struct kref refcount;
 	const struct dma_fence_ops *ops;
-	struct rcu_head rcu;
-	struct list_head cb_list;
+	/* We clear the callback list on kref_put so that by the time we
+	 * release the fence it is unused. No one should be adding to the cb_list
+	 * that they don't themselves hold a reference for.
+	 */
+	union {
+		struct rcu_head rcu;
+		struct list_head cb_list;
+	};
 	spinlock_t *lock;
 	u64 context;
 	u64 seqno;
-- 
2.28.0