1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * Sleepable Read-Copy Update mechanism for mutual exclusion, 4 * tiny version for non-preemptible single-CPU use. 5 * 6 * Copyright (C) IBM Corporation, 2017 7 * 8 * Author: Paul McKenney <paulmck@linux.ibm.com> 9 */ 10 11 #include <linux/export.h> 12 #include <linux/mutex.h> 13 #include <linux/preempt.h> 14 #include <linux/rcupdate_wait.h> 15 #include <linux/sched.h> 16 #include <linux/delay.h> 17 #include <linux/srcu.h> 18 19 #include <linux/rcu_node_tree.h> 20 #include "rcu_segcblist.h" 21 #include "rcu.h" 22 23 int rcu_scheduler_active __read_mostly; 24 static LIST_HEAD(srcu_boot_list); 25 static bool srcu_init_done; 26 27 static int init_srcu_struct_fields(struct srcu_struct *ssp) 28 { 29 ssp->srcu_lock_nesting[0] = 0; 30 ssp->srcu_lock_nesting[1] = 0; 31 init_swait_queue_head(&ssp->srcu_wq); 32 ssp->srcu_cb_head = NULL; 33 ssp->srcu_cb_tail = &ssp->srcu_cb_head; 34 ssp->srcu_gp_running = false; 35 ssp->srcu_gp_waiting = false; 36 ssp->srcu_idx = 0; 37 ssp->srcu_idx_max = 0; 38 INIT_WORK(&ssp->srcu_work, srcu_drive_gp); 39 INIT_LIST_HEAD(&ssp->srcu_work.entry); 40 return 0; 41 } 42 43 #ifdef CONFIG_DEBUG_LOCK_ALLOC 44 45 int __init_srcu_struct(struct srcu_struct *ssp, const char *name, 46 struct lock_class_key *key) 47 { 48 /* Don't re-initialize a lock while it is held. */ 49 debug_check_no_locks_freed((void *)ssp, sizeof(*ssp)); 50 lockdep_init_map(&ssp->dep_map, name, key, 0); 51 return init_srcu_struct_fields(ssp); 52 } 53 EXPORT_SYMBOL_GPL(__init_srcu_struct); 54 55 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 56 57 /* 58 * init_srcu_struct - initialize a sleep-RCU structure 59 * @ssp: structure to initialize. 60 * 61 * Must invoke this on a given srcu_struct before passing that srcu_struct 62 * to any other function. Each srcu_struct represents a separate domain 63 * of SRCU protection. 64 */ 65 int init_srcu_struct(struct srcu_struct *ssp) 66 { 67 return init_srcu_struct_fields(ssp); 68 } 69 EXPORT_SYMBOL_GPL(init_srcu_struct); 70 71 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 72 73 /* 74 * cleanup_srcu_struct - deconstruct a sleep-RCU structure 75 * @ssp: structure to clean up. 76 * 77 * Must invoke this after you are finished using a given srcu_struct that 78 * was initialized via init_srcu_struct(), else you leak memory. 79 */ 80 void cleanup_srcu_struct(struct srcu_struct *ssp) 81 { 82 WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]); 83 flush_work(&ssp->srcu_work); 84 WARN_ON(ssp->srcu_gp_running); 85 WARN_ON(ssp->srcu_gp_waiting); 86 WARN_ON(ssp->srcu_cb_head); 87 WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail); 88 WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max); 89 WARN_ON(ssp->srcu_idx & 0x1); 90 } 91 EXPORT_SYMBOL_GPL(cleanup_srcu_struct); 92 93 /* 94 * Removes the count for the old reader from the appropriate element of 95 * the srcu_struct. 96 */ 97 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) 98 { 99 int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1; 100 101 WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval); 102 if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task()) 103 swake_up_one(&ssp->srcu_wq); 104 } 105 EXPORT_SYMBOL_GPL(__srcu_read_unlock); 106 107 /* 108 * Workqueue handler to drive one grace period and invoke any callbacks 109 * that become ready as a result. Single-CPU and !PREEMPTION operation 110 * means that we get away with murder on synchronization. ;-) 111 */ 112 void srcu_drive_gp(struct work_struct *wp) 113 { 114 int idx; 115 struct rcu_head *lh; 116 struct rcu_head *rhp; 117 struct srcu_struct *ssp; 118 119 ssp = container_of(wp, struct srcu_struct, srcu_work); 120 if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) 121 return; /* Already running or nothing to do. */ 122 123 /* Remove recently arrived callbacks and wait for readers. */ 124 WRITE_ONCE(ssp->srcu_gp_running, true); 125 local_irq_disable(); 126 lh = ssp->srcu_cb_head; 127 ssp->srcu_cb_head = NULL; 128 ssp->srcu_cb_tail = &ssp->srcu_cb_head; 129 local_irq_enable(); 130 idx = (ssp->srcu_idx & 0x2) / 2; 131 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); 132 WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ 133 swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); 134 WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ 135 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); 136 137 /* Invoke the callbacks we removed above. */ 138 while (lh) { 139 rhp = lh; 140 lh = lh->next; 141 debug_rcu_head_callback(rhp); 142 local_bh_disable(); 143 rhp->func(rhp); 144 local_bh_enable(); 145 } 146 147 /* 148 * Enable rescheduling, and if there are more callbacks, 149 * reschedule ourselves. This can race with a call_srcu() 150 * at interrupt level, but the ->srcu_gp_running checks will 151 * straighten that out. 152 */ 153 WRITE_ONCE(ssp->srcu_gp_running, false); 154 if (ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) 155 schedule_work(&ssp->srcu_work); 156 } 157 EXPORT_SYMBOL_GPL(srcu_drive_gp); 158 159 static void srcu_gp_start_if_needed(struct srcu_struct *ssp) 160 { 161 unsigned long cookie; 162 163 cookie = get_state_synchronize_srcu(ssp); 164 if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) 165 return; 166 WRITE_ONCE(ssp->srcu_idx_max, cookie); 167 if (!READ_ONCE(ssp->srcu_gp_running)) { 168 if (likely(srcu_init_done)) 169 schedule_work(&ssp->srcu_work); 170 else if (list_empty(&ssp->srcu_work.entry)) 171 list_add(&ssp->srcu_work.entry, &srcu_boot_list); 172 } 173 } 174 175 /* 176 * Enqueue an SRCU callback on the specified srcu_struct structure, 177 * initiating grace-period processing if it is not already running. 178 */ 179 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, 180 rcu_callback_t func) 181 { 182 unsigned long flags; 183 184 rhp->func = func; 185 rhp->next = NULL; 186 local_irq_save(flags); 187 *ssp->srcu_cb_tail = rhp; 188 ssp->srcu_cb_tail = &rhp->next; 189 local_irq_restore(flags); 190 srcu_gp_start_if_needed(ssp); 191 } 192 EXPORT_SYMBOL_GPL(call_srcu); 193 194 /* 195 * synchronize_srcu - wait for prior SRCU read-side critical-section completion 196 */ 197 void synchronize_srcu(struct srcu_struct *ssp) 198 { 199 struct rcu_synchronize rs; 200 201 srcu_lock_sync(&ssp->dep_map); 202 203 RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || 204 lock_is_held(&rcu_bh_lock_map) || 205 lock_is_held(&rcu_lock_map) || 206 lock_is_held(&rcu_sched_lock_map), 207 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section"); 208 209 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) 210 return; 211 212 might_sleep(); 213 init_rcu_head_on_stack(&rs.head); 214 init_completion(&rs.completion); 215 call_srcu(ssp, &rs.head, wakeme_after_rcu); 216 wait_for_completion(&rs.completion); 217 destroy_rcu_head_on_stack(&rs.head); 218 } 219 EXPORT_SYMBOL_GPL(synchronize_srcu); 220 221 /* 222 * get_state_synchronize_srcu - Provide an end-of-grace-period cookie 223 */ 224 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) 225 { 226 unsigned long ret; 227 228 barrier(); 229 ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1; 230 barrier(); 231 return ret; 232 } 233 EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); 234 235 /* 236 * start_poll_synchronize_srcu - Provide cookie and start grace period 237 * 238 * The difference between this and get_state_synchronize_srcu() is that 239 * this function ensures that the poll_state_synchronize_srcu() will 240 * eventually return the value true. 241 */ 242 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) 243 { 244 unsigned long ret = get_state_synchronize_srcu(ssp); 245 246 srcu_gp_start_if_needed(ssp); 247 return ret; 248 } 249 EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); 250 251 /* 252 * poll_state_synchronize_srcu - Has cookie's grace period ended? 253 */ 254 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) 255 { 256 unsigned long cur_s = READ_ONCE(ssp->srcu_idx); 257 258 barrier(); 259 return ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3); 260 } 261 EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); 262 263 /* Lockdep diagnostics. */ 264 void __init rcu_scheduler_starting(void) 265 { 266 rcu_scheduler_active = RCU_SCHEDULER_RUNNING; 267 } 268 269 /* 270 * Queue work for srcu_struct structures with early boot callbacks. 271 * The work won't actually execute until the workqueue initialization 272 * phase that takes place after the scheduler starts. 273 */ 274 void __init srcu_init(void) 275 { 276 struct srcu_struct *ssp; 277 278 srcu_init_done = true; 279 while (!list_empty(&srcu_boot_list)) { 280 ssp = list_first_entry(&srcu_boot_list, 281 struct srcu_struct, srcu_work.entry); 282 list_del_init(&ssp->srcu_work.entry); 283 schedule_work(&ssp->srcu_work); 284 } 285 } 286