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; 100 101 preempt_disable(); // Needed for PREEMPT_AUTO 102 newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1; 103 WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval); 104 preempt_enable(); 105 if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task()) 106 swake_up_one(&ssp->srcu_wq); 107 } 108 EXPORT_SYMBOL_GPL(__srcu_read_unlock); 109 110 /* 111 * Workqueue handler to drive one grace period and invoke any callbacks 112 * that become ready as a result. Single-CPU and !PREEMPTION operation 113 * means that we get away with murder on synchronization. ;-) 114 */ 115 void srcu_drive_gp(struct work_struct *wp) 116 { 117 int idx; 118 struct rcu_head *lh; 119 struct rcu_head *rhp; 120 struct srcu_struct *ssp; 121 122 ssp = container_of(wp, struct srcu_struct, srcu_work); 123 preempt_disable(); // Needed for PREEMPT_AUTO 124 if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) { 125 return; /* Already running or nothing to do. */ 126 preempt_enable(); 127 } 128 129 /* Remove recently arrived callbacks and wait for readers. */ 130 WRITE_ONCE(ssp->srcu_gp_running, true); 131 local_irq_disable(); 132 lh = ssp->srcu_cb_head; 133 ssp->srcu_cb_head = NULL; 134 ssp->srcu_cb_tail = &ssp->srcu_cb_head; 135 local_irq_enable(); 136 idx = (ssp->srcu_idx & 0x2) / 2; 137 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); 138 WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ 139 preempt_enable(); 140 swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); 141 preempt_disable(); // Needed for PREEMPT_AUTO 142 WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ 143 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); 144 preempt_enable(); 145 146 /* Invoke the callbacks we removed above. */ 147 while (lh) { 148 rhp = lh; 149 lh = lh->next; 150 debug_rcu_head_callback(rhp); 151 local_bh_disable(); 152 rhp->func(rhp); 153 local_bh_enable(); 154 } 155 156 /* 157 * Enable rescheduling, and if there are more callbacks, 158 * reschedule ourselves. This can race with a call_srcu() 159 * at interrupt level, but the ->srcu_gp_running checks will 160 * straighten that out. 161 */ 162 preempt_disable(); // Needed for PREEMPT_AUTO 163 WRITE_ONCE(ssp->srcu_gp_running, false); 164 idx = ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)); 165 preempt_enable(); 166 if (idx) 167 schedule_work(&ssp->srcu_work); 168 } 169 EXPORT_SYMBOL_GPL(srcu_drive_gp); 170 171 static void srcu_gp_start_if_needed(struct srcu_struct *ssp) 172 { 173 unsigned long cookie; 174 175 preempt_disable(); // Needed for PREEMPT_AUTO 176 cookie = get_state_synchronize_srcu(ssp); 177 if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) { 178 preempt_enable(); 179 return; 180 } 181 WRITE_ONCE(ssp->srcu_idx_max, cookie); 182 if (!READ_ONCE(ssp->srcu_gp_running)) { 183 if (likely(srcu_init_done)) 184 schedule_work(&ssp->srcu_work); 185 else if (list_empty(&ssp->srcu_work.entry)) 186 list_add(&ssp->srcu_work.entry, &srcu_boot_list); 187 } 188 preempt_enable(); 189 } 190 191 /* 192 * Enqueue an SRCU callback on the specified srcu_struct structure, 193 * initiating grace-period processing if it is not already running. 194 */ 195 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, 196 rcu_callback_t func) 197 { 198 unsigned long flags; 199 200 rhp->func = func; 201 rhp->next = NULL; 202 preempt_disable(); // Needed for PREEMPT_AUTO 203 local_irq_save(flags); 204 *ssp->srcu_cb_tail = rhp; 205 ssp->srcu_cb_tail = &rhp->next; 206 local_irq_restore(flags); 207 srcu_gp_start_if_needed(ssp); 208 preempt_enable(); 209 } 210 EXPORT_SYMBOL_GPL(call_srcu); 211 212 /* 213 * synchronize_srcu - wait for prior SRCU read-side critical-section completion 214 */ 215 void synchronize_srcu(struct srcu_struct *ssp) 216 { 217 struct rcu_synchronize rs; 218 219 srcu_lock_sync(&ssp->dep_map); 220 221 RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || 222 lock_is_held(&rcu_bh_lock_map) || 223 lock_is_held(&rcu_lock_map) || 224 lock_is_held(&rcu_sched_lock_map), 225 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section"); 226 227 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) 228 return; 229 230 might_sleep(); 231 init_rcu_head_on_stack(&rs.head); 232 init_completion(&rs.completion); 233 call_srcu(ssp, &rs.head, wakeme_after_rcu); 234 wait_for_completion(&rs.completion); 235 destroy_rcu_head_on_stack(&rs.head); 236 } 237 EXPORT_SYMBOL_GPL(synchronize_srcu); 238 239 /* 240 * get_state_synchronize_srcu - Provide an end-of-grace-period cookie 241 */ 242 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) 243 { 244 unsigned long ret; 245 246 barrier(); 247 ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1; 248 barrier(); 249 return ret; 250 } 251 EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); 252 253 /* 254 * start_poll_synchronize_srcu - Provide cookie and start grace period 255 * 256 * The difference between this and get_state_synchronize_srcu() is that 257 * this function ensures that the poll_state_synchronize_srcu() will 258 * eventually return the value true. 259 */ 260 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) 261 { 262 unsigned long ret; 263 264 preempt_disable(); // Needed for PREEMPT_AUTO 265 ret = get_state_synchronize_srcu(ssp); 266 srcu_gp_start_if_needed(ssp); 267 preempt_enable(); 268 return ret; 269 } 270 EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); 271 272 /* 273 * poll_state_synchronize_srcu - Has cookie's grace period ended? 274 */ 275 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) 276 { 277 unsigned long cur_s = READ_ONCE(ssp->srcu_idx); 278 279 barrier(); 280 return cookie == SRCU_GET_STATE_COMPLETED || 281 ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3); 282 } 283 EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); 284 285 /* Lockdep diagnostics. */ 286 void __init rcu_scheduler_starting(void) 287 { 288 rcu_scheduler_active = RCU_SCHEDULER_RUNNING; 289 } 290 291 /* 292 * Queue work for srcu_struct structures with early boot callbacks. 293 * The work won't actually execute until the workqueue initialization 294 * phase that takes place after the scheduler starts. 295 */ 296 void __init srcu_init(void) 297 { 298 struct srcu_struct *ssp; 299 300 srcu_init_done = true; 301 while (!list_empty(&srcu_boot_list)) { 302 ssp = list_first_entry(&srcu_boot_list, 303 struct srcu_struct, srcu_work.entry); 304 list_del_init(&ssp->srcu_work.entry); 305 schedule_work(&ssp->srcu_work); 306 } 307 } 308