1 /* 2 * Sleepable Read-Copy Update mechanism for mutual exclusion, 3 * tiny version for non-preemptible single-CPU use. 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms of the GNU General Public License as published by 7 * the Free Software Foundation; either version 2 of the License, or 8 * (at your option) any later version. 9 * 10 * This program is distributed in the hope that it will be useful, 11 * but WITHOUT ANY WARRANTY; without even the implied warranty of 12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 * GNU General Public License for more details. 14 * 15 * You should have received a copy of the GNU General Public License 16 * along with this program; if not, you can access it online at 17 * http://www.gnu.org/licenses/gpl-2.0.html. 18 * 19 * Copyright (C) IBM Corporation, 2017 20 * 21 * Author: Paul McKenney <paulmck@us.ibm.com> 22 */ 23 24 #include <linux/export.h> 25 #include <linux/mutex.h> 26 #include <linux/preempt.h> 27 #include <linux/rcupdate_wait.h> 28 #include <linux/sched.h> 29 #include <linux/delay.h> 30 #include <linux/srcu.h> 31 32 #include <linux/rcu_node_tree.h> 33 #include "rcu_segcblist.h" 34 #include "rcu.h" 35 36 static int init_srcu_struct_fields(struct srcu_struct *sp) 37 { 38 sp->srcu_lock_nesting[0] = 0; 39 sp->srcu_lock_nesting[1] = 0; 40 init_swait_queue_head(&sp->srcu_wq); 41 sp->srcu_cb_head = NULL; 42 sp->srcu_cb_tail = &sp->srcu_cb_head; 43 sp->srcu_gp_running = false; 44 sp->srcu_gp_waiting = false; 45 sp->srcu_idx = 0; 46 INIT_WORK(&sp->srcu_work, srcu_drive_gp); 47 return 0; 48 } 49 50 #ifdef CONFIG_DEBUG_LOCK_ALLOC 51 52 int __init_srcu_struct(struct srcu_struct *sp, const char *name, 53 struct lock_class_key *key) 54 { 55 /* Don't re-initialize a lock while it is held. */ 56 debug_check_no_locks_freed((void *)sp, sizeof(*sp)); 57 lockdep_init_map(&sp->dep_map, name, key, 0); 58 return init_srcu_struct_fields(sp); 59 } 60 EXPORT_SYMBOL_GPL(__init_srcu_struct); 61 62 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 63 64 /* 65 * init_srcu_struct - initialize a sleep-RCU structure 66 * @sp: structure to initialize. 67 * 68 * Must invoke this on a given srcu_struct before passing that srcu_struct 69 * to any other function. Each srcu_struct represents a separate domain 70 * of SRCU protection. 71 */ 72 int init_srcu_struct(struct srcu_struct *sp) 73 { 74 return init_srcu_struct_fields(sp); 75 } 76 EXPORT_SYMBOL_GPL(init_srcu_struct); 77 78 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 79 80 /* 81 * cleanup_srcu_struct - deconstruct a sleep-RCU structure 82 * @sp: structure to clean up. 83 * 84 * Must invoke this after you are finished using a given srcu_struct that 85 * was initialized via init_srcu_struct(), else you leak memory. 86 */ 87 void cleanup_srcu_struct(struct srcu_struct *sp) 88 { 89 WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]); 90 flush_work(&sp->srcu_work); 91 WARN_ON(sp->srcu_gp_running); 92 WARN_ON(sp->srcu_gp_waiting); 93 WARN_ON(sp->srcu_cb_head); 94 WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail); 95 } 96 EXPORT_SYMBOL_GPL(cleanup_srcu_struct); 97 98 /* 99 * Removes the count for the old reader from the appropriate element of 100 * the srcu_struct. 101 */ 102 void __srcu_read_unlock(struct srcu_struct *sp, int idx) 103 { 104 int newval = sp->srcu_lock_nesting[idx] - 1; 105 106 WRITE_ONCE(sp->srcu_lock_nesting[idx], newval); 107 if (!newval && READ_ONCE(sp->srcu_gp_waiting)) 108 swake_up(&sp->srcu_wq); 109 } 110 EXPORT_SYMBOL_GPL(__srcu_read_unlock); 111 112 /* 113 * Workqueue handler to drive one grace period and invoke any callbacks 114 * that become ready as a result. Single-CPU and !PREEMPT operation 115 * means that we get away with murder on synchronization. ;-) 116 */ 117 void srcu_drive_gp(struct work_struct *wp) 118 { 119 int idx; 120 struct rcu_head *lh; 121 struct rcu_head *rhp; 122 struct srcu_struct *sp; 123 124 sp = container_of(wp, struct srcu_struct, srcu_work); 125 if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head)) 126 return; /* Already running or nothing to do. */ 127 128 /* Remove recently arrived callbacks and wait for readers. */ 129 WRITE_ONCE(sp->srcu_gp_running, true); 130 local_irq_disable(); 131 lh = sp->srcu_cb_head; 132 sp->srcu_cb_head = NULL; 133 sp->srcu_cb_tail = &sp->srcu_cb_head; 134 local_irq_enable(); 135 idx = sp->srcu_idx; 136 WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx); 137 WRITE_ONCE(sp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ 138 swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx])); 139 WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ 140 141 /* Invoke the callbacks we removed above. */ 142 while (lh) { 143 rhp = lh; 144 lh = lh->next; 145 local_bh_disable(); 146 rhp->func(rhp); 147 local_bh_enable(); 148 } 149 150 /* 151 * Enable rescheduling, and if there are more callbacks, 152 * reschedule ourselves. This can race with a call_srcu() 153 * at interrupt level, but the ->srcu_gp_running checks will 154 * straighten that out. 155 */ 156 WRITE_ONCE(sp->srcu_gp_running, false); 157 if (READ_ONCE(sp->srcu_cb_head)) 158 schedule_work(&sp->srcu_work); 159 } 160 EXPORT_SYMBOL_GPL(srcu_drive_gp); 161 162 /* 163 * Enqueue an SRCU callback on the specified srcu_struct structure, 164 * initiating grace-period processing if it is not already running. 165 */ 166 void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, 167 rcu_callback_t func) 168 { 169 unsigned long flags; 170 171 rhp->func = func; 172 rhp->next = NULL; 173 local_irq_save(flags); 174 *sp->srcu_cb_tail = rhp; 175 sp->srcu_cb_tail = &rhp->next; 176 local_irq_restore(flags); 177 if (!READ_ONCE(sp->srcu_gp_running)) 178 schedule_work(&sp->srcu_work); 179 } 180 EXPORT_SYMBOL_GPL(call_srcu); 181 182 /* 183 * synchronize_srcu - wait for prior SRCU read-side critical-section completion 184 */ 185 void synchronize_srcu(struct srcu_struct *sp) 186 { 187 struct rcu_synchronize rs; 188 189 init_rcu_head_on_stack(&rs.head); 190 init_completion(&rs.completion); 191 call_srcu(sp, &rs.head, wakeme_after_rcu); 192 wait_for_completion(&rs.completion); 193 destroy_rcu_head_on_stack(&rs.head); 194 } 195 EXPORT_SYMBOL_GPL(synchronize_srcu); 196