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/irq_work.h> 13 #include <linux/mutex.h> 14 #include <linux/preempt.h> 15 #include <linux/rcupdate_wait.h> 16 #include <linux/sched.h> 17 #include <linux/delay.h> 18 #include <linux/srcu.h> 19 20 #include <linux/rcu_node_tree.h> 21 #include "rcu_segcblist.h" 22 #include "rcu.h" 23 24 #ifndef CONFIG_TREE_RCU 25 int rcu_scheduler_active __read_mostly; 26 #else // #ifndef CONFIG_TREE_RCU 27 extern int rcu_scheduler_active; 28 #endif // #else // #ifndef CONFIG_TREE_RCU 29 static LIST_HEAD(srcu_boot_list); 30 static bool srcu_init_done; 31 32 static int init_srcu_struct_fields(struct srcu_struct *ssp) 33 { 34 ssp->srcu_lock_nesting[0] = 0; 35 ssp->srcu_lock_nesting[1] = 0; 36 init_swait_queue_head(&ssp->srcu_wq); 37 ssp->srcu_cb_head = NULL; 38 ssp->srcu_cb_tail = &ssp->srcu_cb_head; 39 ssp->srcu_gp_running = false; 40 ssp->srcu_gp_waiting = false; 41 ssp->srcu_idx = 0; 42 ssp->srcu_idx_max = 0; 43 INIT_WORK(&ssp->srcu_work, srcu_drive_gp); 44 INIT_LIST_HEAD(&ssp->srcu_work.entry); 45 init_irq_work(&ssp->srcu_irq_work, srcu_tiny_irq_work); 46 return 0; 47 } 48 49 #ifdef CONFIG_DEBUG_LOCK_ALLOC 50 51 int __init_srcu_struct(struct srcu_struct *ssp, const char *name, 52 struct lock_class_key *key) 53 { 54 /* Don't re-initialize a lock while it is held. */ 55 debug_check_no_locks_freed((void *)ssp, sizeof(*ssp)); 56 lockdep_init_map(&ssp->dep_map, name, key, 0); 57 return init_srcu_struct_fields(ssp); 58 } 59 EXPORT_SYMBOL_GPL(__init_srcu_struct); 60 61 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 62 63 /* 64 * init_srcu_struct - initialize a sleep-RCU structure 65 * @ssp: structure to initialize. 66 * 67 * Must invoke this on a given srcu_struct before passing that srcu_struct 68 * to any other function. Each srcu_struct represents a separate domain 69 * of SRCU protection. 70 */ 71 int init_srcu_struct(struct srcu_struct *ssp) 72 { 73 return init_srcu_struct_fields(ssp); 74 } 75 EXPORT_SYMBOL_GPL(init_srcu_struct); 76 77 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 78 79 /* 80 * cleanup_srcu_struct - deconstruct a sleep-RCU structure 81 * @ssp: structure to clean up. 82 * 83 * Must invoke this after you are finished using a given srcu_struct that 84 * was initialized via init_srcu_struct(), else you leak memory. 85 */ 86 void cleanup_srcu_struct(struct srcu_struct *ssp) 87 { 88 WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]); 89 irq_work_sync(&ssp->srcu_irq_work); 90 flush_work(&ssp->srcu_work); 91 WARN_ON(ssp->srcu_gp_running); 92 WARN_ON(ssp->srcu_gp_waiting); 93 WARN_ON(ssp->srcu_cb_head); 94 WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail); 95 WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max); 96 WARN_ON(ssp->srcu_idx & 0x1); 97 } 98 EXPORT_SYMBOL_GPL(cleanup_srcu_struct); 99 100 /* 101 * Removes the count for the old reader from the appropriate element of 102 * the srcu_struct. 103 */ 104 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) 105 { 106 int newval; 107 108 preempt_disable(); // Needed for PREEMPT_LAZY 109 newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1; 110 WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval); 111 preempt_enable(); 112 if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task() && !irqs_disabled()) 113 swake_up_one(&ssp->srcu_wq); 114 } 115 EXPORT_SYMBOL_GPL(__srcu_read_unlock); 116 117 /* 118 * Workqueue handler to drive one grace period and invoke any callbacks 119 * that become ready as a result. Single-CPU operation and preemption 120 * disabling mean that we get away with murder on synchronization. ;-) 121 */ 122 void srcu_drive_gp(struct work_struct *wp) 123 { 124 int idx; 125 struct rcu_head *lh; 126 struct rcu_head *rhp; 127 struct srcu_struct *ssp; 128 129 ssp = container_of(wp, struct srcu_struct, srcu_work); 130 preempt_disable(); // Needed for PREEMPT_LAZY 131 if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) { 132 preempt_enable(); 133 return; /* Already running or nothing to do. */ 134 } 135 136 /* Remove recently arrived callbacks and wait for readers. */ 137 WRITE_ONCE(ssp->srcu_gp_running, true); 138 local_irq_disable(); 139 lh = ssp->srcu_cb_head; 140 ssp->srcu_cb_head = NULL; 141 ssp->srcu_cb_tail = &ssp->srcu_cb_head; 142 local_irq_enable(); 143 idx = (ssp->srcu_idx & 0x2) / 2; 144 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); 145 WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ 146 preempt_enable(); 147 do { 148 // Deadlock issues prevent __srcu_read_unlock() from 149 // doing an unconditional wakeup, so polling is required. 150 swait_event_timeout_exclusive(ssp->srcu_wq, 151 !READ_ONCE(ssp->srcu_lock_nesting[idx]), HZ / 10); 152 } while (READ_ONCE(ssp->srcu_lock_nesting[idx])); 153 preempt_disable(); // Needed for PREEMPT_LAZY 154 WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ 155 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); 156 preempt_enable(); 157 158 /* Invoke the callbacks we removed above. */ 159 while (lh) { 160 rhp = lh; 161 lh = lh->next; 162 debug_rcu_head_callback(rhp); 163 local_bh_disable(); 164 rhp->func(rhp); 165 local_bh_enable(); 166 } 167 168 /* 169 * Enable rescheduling, and if there are more callbacks, 170 * reschedule ourselves. This can race with a call_srcu() 171 * at interrupt level, but the ->srcu_gp_running checks will 172 * straighten that out. 173 */ 174 preempt_disable(); // Needed for PREEMPT_LAZY 175 WRITE_ONCE(ssp->srcu_gp_running, false); 176 idx = ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)); 177 preempt_enable(); 178 if (idx) 179 schedule_work(&ssp->srcu_work); 180 } 181 EXPORT_SYMBOL_GPL(srcu_drive_gp); 182 183 /* 184 * Use an irq_work to defer schedule_work() to avoid acquiring the workqueue 185 * pool->lock while the caller might hold scheduler locks, causing lockdep 186 * splats due to workqueue_init() doing a wakeup. 187 */ 188 void srcu_tiny_irq_work(struct irq_work *irq_work) 189 { 190 struct srcu_struct *ssp; 191 192 ssp = container_of(irq_work, struct srcu_struct, srcu_irq_work); 193 schedule_work(&ssp->srcu_work); 194 } 195 EXPORT_SYMBOL_GPL(srcu_tiny_irq_work); 196 197 static void srcu_gp_start_if_needed(struct srcu_struct *ssp) 198 { 199 unsigned long cookie; 200 201 lockdep_assert_preemption_disabled(); // Needed for PREEMPT_LAZY 202 cookie = get_state_synchronize_srcu(ssp); 203 if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) { 204 return; 205 } 206 WRITE_ONCE(ssp->srcu_idx_max, cookie); 207 if (!READ_ONCE(ssp->srcu_gp_running)) { 208 if (likely(srcu_init_done)) 209 irq_work_queue(&ssp->srcu_irq_work); 210 else if (list_empty(&ssp->srcu_work.entry)) 211 list_add(&ssp->srcu_work.entry, &srcu_boot_list); 212 } 213 } 214 215 /* 216 * Enqueue an SRCU callback on the specified srcu_struct structure, 217 * initiating grace-period processing if it is not already running. 218 */ 219 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, 220 rcu_callback_t func) 221 { 222 unsigned long flags; 223 224 rhp->func = func; 225 rhp->next = NULL; 226 preempt_disable(); // Needed for PREEMPT_LAZY 227 local_irq_save(flags); 228 *ssp->srcu_cb_tail = rhp; 229 ssp->srcu_cb_tail = &rhp->next; 230 local_irq_restore(flags); 231 srcu_gp_start_if_needed(ssp); 232 preempt_enable(); 233 } 234 EXPORT_SYMBOL_GPL(call_srcu); 235 236 /* 237 * synchronize_srcu - wait for prior SRCU read-side critical-section completion 238 */ 239 void synchronize_srcu(struct srcu_struct *ssp) 240 { 241 struct rcu_synchronize rs; 242 243 srcu_lock_sync(&ssp->dep_map); 244 245 RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || 246 lock_is_held(&rcu_bh_lock_map) || 247 lock_is_held(&rcu_lock_map) || 248 lock_is_held(&rcu_sched_lock_map), 249 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section"); 250 251 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) 252 return; 253 254 might_sleep(); 255 init_rcu_head_on_stack(&rs.head); 256 init_completion(&rs.completion); 257 call_srcu(ssp, &rs.head, wakeme_after_rcu); 258 wait_for_completion(&rs.completion); 259 destroy_rcu_head_on_stack(&rs.head); 260 } 261 EXPORT_SYMBOL_GPL(synchronize_srcu); 262 263 /* 264 * get_state_synchronize_srcu - Provide an end-of-grace-period cookie 265 */ 266 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) 267 { 268 unsigned long ret; 269 270 barrier(); 271 ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1; 272 barrier(); 273 return ret; 274 } 275 EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); 276 277 /* 278 * start_poll_synchronize_srcu - Provide cookie and start grace period 279 * 280 * The difference between this and get_state_synchronize_srcu() is that 281 * this function ensures that the poll_state_synchronize_srcu() will 282 * eventually return the value true. 283 */ 284 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) 285 { 286 unsigned long ret; 287 288 preempt_disable(); // Needed for PREEMPT_LAZY 289 ret = get_state_synchronize_srcu(ssp); 290 srcu_gp_start_if_needed(ssp); 291 preempt_enable(); 292 return ret; 293 } 294 EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); 295 296 /* 297 * poll_state_synchronize_srcu - Has cookie's grace period ended? 298 */ 299 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) 300 { 301 unsigned long cur_s = READ_ONCE(ssp->srcu_idx); 302 303 barrier(); 304 return cookie == SRCU_GET_STATE_COMPLETED || 305 ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3); 306 } 307 EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); 308 309 #ifndef CONFIG_TREE_RCU 310 /* Lockdep diagnostics. */ 311 void __init rcu_scheduler_starting(void) 312 { 313 rcu_scheduler_active = RCU_SCHEDULER_RUNNING; 314 } 315 #endif // #ifndef CONFIG_TREE_RCU 316 317 /* 318 * Queue work for srcu_struct structures with early boot callbacks. 319 * The work won't actually execute until the workqueue initialization 320 * phase that takes place after the scheduler starts. 321 */ 322 void __init srcu_init(void) 323 { 324 struct srcu_struct *ssp; 325 326 srcu_init_done = true; 327 while (!list_empty(&srcu_boot_list)) { 328 ssp = list_first_entry(&srcu_boot_list, 329 struct srcu_struct, srcu_work.entry); 330 list_del_init(&ssp->srcu_work.entry); 331 schedule_work(&ssp->srcu_work); 332 } 333 } 334