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()
679 			 *    have been previously pushed. This pairs with  in data_push_tail()
706 			 *    have been previously pushed. This pairs with  in data_push_tail()
744 		 * the descriptor states reusable. This pairs with  in data_push_tail()
830 		 * descriptor states reusable. This pairs with desc_reserve:D.  in desc_push_tail()
838 		 * case that the descriptor has been recycled. This pairs  in desc_push_tail()
891 		 * ID. This pairs with desc_reserve:D.  in desc_reserve()
924 		 *    sufficient for this. This pairs with desc_push_tail:B.  in desc_reserve()
943 		 *    ID. This pairs with desc_reserve:B.  in desc_reserve()
949 		 *    pushed the data ring tails. This pairs with  in desc_reserve()
954 		 *    another CPU may have pushed the tail ID. This pairs  in desc_reserve()
955 		 *    with desc_push_tail:C and this also pairs with  in desc_reserve()
959 		 *    finalize the previous descriptor. This pairs with  in desc_reserve()
984 	 * This pairs with desc_read:D.  in desc_reserve()
1056 		 *    states are visible. This pairs with desc_read:D.  in data_alloc()
1065 		 *    pairs with data_push_tail:B.  in data_alloc()
1283 	 * modification is followed by reading. This pairs with _prb_commit:B.  in desc_reopen_last()
1584 	 *    for this. This pairs with desc_read:B and desc_reopen_last:A.  in _prb_commit()
1588 	 *    descriptor. This pairs with desc_reserve:D.  in _prb_commit()
1847 		 * that the descriptor has been recycled. This pairs with  in prb_first_seq()