269  * The memory barrier pairs and their ordering are:
457 	 * not apply to the descriptor state. This pairs with _prb_commit:B.  in desc_read()
487 	 *    that may not apply to the copied content. This pairs with  in desc_read()
503 	 *    not apply to the copied data. This pairs with data_alloc:A and  in desc_read()
643 	 * CPU. This pairs with data_push_tail:D.  in data_push_tail()
680 			 *    have been previously pushed. This pairs with  in data_push_tail()
707 			 *    have been previously pushed. This pairs with  in data_push_tail()
745 		 * the descriptor states reusable. This pairs with  in data_push_tail()
831 		 * descriptor states reusable. This pairs with desc_reserve:D.  in desc_push_tail()
839 		 * case that the descriptor has been recycled. This pairs  in desc_push_tail()
892 		 * ID. This pairs with desc_reserve:D.  in desc_reserve()
925 		 *    sufficient for this. This pairs with desc_push_tail:B.  in desc_reserve()
944 		 *    ID. This pairs with desc_reserve:B.  in desc_reserve()
950 		 *    pushed the data ring tails. This pairs with  in desc_reserve()
955 		 *    another CPU may have pushed the tail ID. This pairs  in desc_reserve()
956 		 *    with desc_push_tail:C and this also pairs with  in desc_reserve()
960 		 *    finalize the previous descriptor. This pairs with  in desc_reserve()
985 	 * This pairs with desc_read:D.  in desc_reserve()
1057 		 *    states are visible. This pairs with desc_read:D.  in data_alloc()
1066 		 *    pairs with data_push_tail:B.  in data_alloc()
1284 	 * modification is followed by reading. This pairs with _prb_commit:B.  in desc_reopen_last()
1586 	 *    for this. This pairs with desc_read:B and desc_reopen_last:A.  in _prb_commit()
1590 	 *    descriptor. This pairs with desc_reserve:D.  in _prb_commit()
1849 		 * that the descriptor has been recycled. This pairs with  in prb_first_seq()