dma-buf: nuke reservation_object seq number

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

Christian König committed 7 years ago

Commit 5d344f51 parent d3c6dd12 files · +7 −26Browse files

Showing the changes to include/linux (1 of 2 files). Show all

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include/linux/reservation.h+2−7

 #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
  */
 struct reservation_object {
 	struct ww_mutex lock;
-	seqcount_t seq;
 	struct dma_fence __rcu *fence_excl;
 	struct reservation_object_list __rcu *fence;
 			  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);
 }
 /**

dma-buf: nuke reservation_object seq number

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