1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* 3 * RCU segmented callback lists 4 * 5 * This seemingly RCU-private file must be available to SRCU users 6 * because the size of the TREE SRCU srcu_struct structure depends 7 * on these definitions. 8 * 9 * Copyright IBM Corporation, 2017 10 * 11 * Authors: Paul E. McKenney <paulmck@linux.net.ibm.com> 12 */ 13 14 #ifndef __INCLUDE_LINUX_RCU_SEGCBLIST_H 15 #define __INCLUDE_LINUX_RCU_SEGCBLIST_H 16 17 /* Simple unsegmented callback lists. */ 18 struct rcu_cblist { 19 struct rcu_head *head; 20 struct rcu_head **tail; 21 long len; 22 long len_lazy; 23 }; 24 25 #define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head } 26 27 /* Complicated segmented callback lists. ;-) */ 28 29 /* 30 * Index values for segments in rcu_segcblist structure. 31 * 32 * The segments are as follows: 33 * 34 * [head, *tails[RCU_DONE_TAIL]): 35 * Callbacks whose grace period has elapsed, and thus can be invoked. 36 * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]): 37 * Callbacks waiting for the current GP from the current CPU's viewpoint. 38 * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]): 39 * Callbacks that arrived before the next GP started, again from 40 * the current CPU's viewpoint. These can be handled by the next GP. 41 * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]): 42 * Callbacks that might have arrived after the next GP started. 43 * There is some uncertainty as to when a given GP starts and 44 * ends, but a CPU knows the exact times if it is the one starting 45 * or ending the GP. Other CPUs know that the previous GP ends 46 * before the next one starts. 47 * 48 * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also 49 * empty. 50 * 51 * The ->gp_seq[] array contains the grace-period number at which the 52 * corresponding segment of callbacks will be ready to invoke. A given 53 * element of this array is meaningful only when the corresponding segment 54 * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks 55 * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have 56 * not yet been assigned a grace-period number). 57 */ 58 #define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */ 59 #define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */ 60 #define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */ 61 #define RCU_NEXT_TAIL 3 62 #define RCU_CBLIST_NSEGS 4 63 64 struct rcu_segcblist { 65 struct rcu_head *head; 66 struct rcu_head **tails[RCU_CBLIST_NSEGS]; 67 unsigned long gp_seq[RCU_CBLIST_NSEGS]; 68 long len; 69 long len_lazy; 70 }; 71 72 #define RCU_SEGCBLIST_INITIALIZER(n) \ 73 { \ 74 .head = NULL, \ 75 .tails[RCU_DONE_TAIL] = &n.head, \ 76 .tails[RCU_WAIT_TAIL] = &n.head, \ 77 .tails[RCU_NEXT_READY_TAIL] = &n.head, \ 78 .tails[RCU_NEXT_TAIL] = &n.head, \ 79 } 80 81 #endif /* __INCLUDE_LINUX_RCU_SEGCBLIST_H */ 82