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