The only remaining use for this is to protect against setting a new exclusive
fence while we grab both exclusive and shared. That can also be archived by
looking if the exclusive fence has changed or not after completing the
operation.
v2: switch setting excl fence to rcu_assign_pointer
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/dma-buf/reservation.c | 24 +++++-------------------
include/linux/reservation.h | 9 ++-------
2 files changed, 7 insertions(+), 26 deletions(-)
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 90bc6ef03598..f7f4a0858c2a 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -49,12 +49,6 @@
DEFINE_WD_CLASS(reservation_ww_class);
EXPORT_SYMBOL(reservation_ww_class);
-struct lock_class_key reservation_seqcount_class;
-EXPORT_SYMBOL(reservation_seqcount_class);
-
-const char reservation_seqcount_string[] = "reservation_seqcount";
-EXPORT_SYMBOL(reservation_seqcount_string);
-
/**
* reservation_object_list_alloc - allocate fence list
* @shared_max: number of fences we need space for
@@ -103,9 +97,6 @@ static void reservation_object_list_free(struct reservation_object_list *list)
void reservation_object_init(struct reservation_object *obj)
{
ww_mutex_init(&obj->lock, &reservation_ww_class);
-
- __seqcount_init(&obj->seq, reservation_seqcount_string,
- &reservation_seqcount_class);
RCU_INIT_POINTER(obj->fence, NULL);
RCU_INIT_POINTER(obj->fence_excl, NULL);
}
@@ -282,12 +273,10 @@ void reservation_object_add_excl_fence(struct reservation_object *obj,
dma_fence_get(fence);
preempt_disable();
- write_seqcount_begin(&obj->seq);
- /* write_seqcount_begin provides the necessary memory barrier */
- RCU_INIT_POINTER(obj->fence_excl, fence);
+ rcu_assign_pointer(obj->fence_excl, fence);
+ /* pointer update must be visible before we modify the shared_count */
if (old)
- old->shared_count = 0;
- write_seqcount_end(&obj->seq);
+ smp_store_mb(old->shared_count, 0);
preempt_enable();
/* inplace update, no shared fences */
@@ -368,11 +357,8 @@ int reservation_object_copy_fences(struct reservation_object *dst,
old = reservation_object_get_excl(dst);
preempt_disable();
- write_seqcount_begin(&dst->seq);
- /* write_seqcount_begin provides the necessary memory barrier */
- RCU_INIT_POINTER(dst->fence_excl, new);
- RCU_INIT_POINTER(dst->fence, dst_list);
- write_seqcount_end(&dst->seq);
+ rcu_assign_pointer(dst->fence_excl, new);
+ rcu_assign_pointer(dst->fence, dst_list);
preempt_enable();
reservation_object_list_free(src_list);
diff --git a/include/linux/reservation.h b/include/linux/reservation.h
index 044a5cd4af50..fd29baad0be3 100644
--- a/include/linux/reservation.h
+++ b/include/linux/reservation.h
@@ -46,8 +46,6 @@
#include <linux/rcupdate.h>
extern struct ww_class reservation_ww_class;
-extern struct lock_class_key reservation_seqcount_class;
-extern const char reservation_seqcount_string[];
/**
* struct reservation_object_list - a list of shared fences
@@ -71,7 +69,6 @@ struct reservation_object_list {
*/
struct reservation_object {
struct ww_mutex lock;
- seqcount_t seq;
struct dma_fence __rcu *fence_excl;
struct reservation_object_list __rcu *fence;
@@ -156,14 +153,12 @@ reservation_object_fences(struct reservation_object *obj,
struct reservation_object_list **list,
u32 *shared_count)
{
- unsigned int seq;
-
do {
- seq = read_seqcount_begin(&obj->seq);
*excl = rcu_dereference(obj->fence_excl);
*list = rcu_dereference(obj->fence);
*shared_count = *list ? (*list)->shared_count : 0;
- } while (read_seqcount_retry(&obj->seq, seq));
+ smp_rmb(); /* See reservation_object_add_excl_fence */
+ } while (rcu_access_pointer(obj->fence_excl) != *excl);
}
/**
--
2.17.1
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