diff options
Diffstat (limited to 'include/linux/dma-fence.h')
| -rw-r--r-- | include/linux/dma-fence.h | 44 |
1 files changed, 28 insertions, 16 deletions
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 974717d6ac0c..3347c54f3a87 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -1,3 +1,4 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ /* * Fence mechanism for dma-buf to allow for asynchronous dma access * @@ -7,15 +8,6 @@ * Authors: * Rob Clark <robdclark@gmail.com> * Maarten Lankhorst <maarten.lankhorst@canonical.com> - * - * This program is free software; you can redistribute it and/or modify it - * under the terms of the GNU General Public License version 2 as published by - * the Free Software Foundation. - * - * This program is distributed in the hope that it will be useful, but WITHOUT - * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or - * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for - * more details. */ #ifndef __LINUX_DMA_FENCE_H @@ -71,15 +63,35 @@ struct dma_fence_cb; * been completed, or never called at all. */ struct dma_fence { - struct kref refcount; - const struct dma_fence_ops *ops; - struct rcu_head rcu; - struct list_head cb_list; spinlock_t *lock; + const struct dma_fence_ops *ops; + /* + * 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. + * + * The lifetime of the timestamp is similarly tied to both the + * rcu freelist and the cb_list. The timestamp is only set upon + * signaling while simultaneously notifying the cb_list. Ergo, we + * only use either the cb_list of timestamp. Upon destruction, + * neither are accessible, and so we can use the rcu. This means + * that the cb_list is *only* valid until the signal bit is set, + * and to read either you *must* hold a reference to the fence, + * and not just the rcu_read_lock. + * + * Listed in chronological order. + */ + union { + struct list_head cb_list; + /* @cb_list replaced by @timestamp on dma_fence_signal() */ + ktime_t timestamp; + /* @timestamp replaced by @rcu on dma_fence_release() */ + struct rcu_head rcu; + }; u64 context; u64 seqno; unsigned long flags; - ktime_t timestamp; + struct kref refcount; int error; }; @@ -281,7 +293,7 @@ static inline struct dma_fence *dma_fence_get(struct dma_fence *fence) } /** - * dma_fence_get_rcu - get a fence from a reservation_object_list with + * dma_fence_get_rcu - get a fence from a dma_resv_list with * rcu read lock * @fence: fence to increase refcount of * @@ -305,7 +317,7 @@ static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence) * so long as the caller is using RCU on the pointer to the fence. * * An alternative mechanism is to employ a seqlock to protect a bunch of - * fences, such as used by struct reservation_object. When using a seqlock, + * fences, such as used by struct dma_resv. When using a seqlock, * the seqlock must be taken before and checked after a reference to the * fence is acquired (as shown here). * |