1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition. 4 * 5 * Copyright IBM Corporation, 2008 6 * 7 * Author: Paul E. McKenney <paulmck@linux.ibm.com> 8 * 9 * For detailed explanation of Read-Copy Update mechanism see - 10 * Documentation/RCU 11 */ 12 #include <linux/completion.h> 13 #include <linux/interrupt.h> 14 #include <linux/notifier.h> 15 #include <linux/rcupdate_wait.h> 16 #include <linux/kernel.h> 17 #include <linux/export.h> 18 #include <linux/mutex.h> 19 #include <linux/sched.h> 20 #include <linux/types.h> 21 #include <linux/init.h> 22 #include <linux/time.h> 23 #include <linux/cpu.h> 24 #include <linux/prefetch.h> 25 #include <linux/slab.h> 26 #include <linux/mm.h> 27 28 #include "rcu.h" 29 30 /* Global control variables for rcupdate callback mechanism. */ 31 struct rcu_ctrlblk { 32 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ 33 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ 34 struct rcu_head **curtail; /* ->next pointer of last CB. */ 35 unsigned long gp_seq; /* Grace-period counter. */ 36 }; 37 38 /* Definition for rcupdate control block. */ 39 static struct rcu_ctrlblk rcu_ctrlblk = { 40 .donetail = &rcu_ctrlblk.rcucblist, 41 .curtail = &rcu_ctrlblk.rcucblist, 42 .gp_seq = 0 - 300UL, 43 }; 44 45 void rcu_barrier(void) 46 { 47 wait_rcu_gp(call_rcu_hurry); 48 } 49 EXPORT_SYMBOL(rcu_barrier); 50 51 /* Record an rcu quiescent state. */ 52 void rcu_qs(void) 53 { 54 unsigned long flags; 55 56 local_irq_save(flags); 57 if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) { 58 rcu_ctrlblk.donetail = rcu_ctrlblk.curtail; 59 raise_softirq_irqoff(RCU_SOFTIRQ); 60 } 61 WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2); 62 local_irq_restore(flags); 63 } 64 65 /* 66 * Check to see if the scheduling-clock interrupt came from an extended 67 * quiescent state, and, if so, tell RCU about it. This function must 68 * be called from hardirq context. It is normally called from the 69 * scheduling-clock interrupt. 70 */ 71 void rcu_sched_clock_irq(int user) 72 { 73 if (user) 74 rcu_qs(); 75 else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) 76 set_need_resched_current(); 77 } 78 79 /* 80 * Reclaim the specified callback, either by invoking it for non-kfree cases or 81 * freeing it directly (for kfree). Return true if kfreeing, false otherwise. 82 */ 83 static inline bool rcu_reclaim_tiny(struct rcu_head *head) 84 { 85 rcu_callback_t f; 86 87 rcu_lock_acquire(&rcu_callback_map); 88 89 trace_rcu_invoke_callback("", head); 90 f = head->func; 91 debug_rcu_head_callback(head); 92 WRITE_ONCE(head->func, (rcu_callback_t)0L); 93 f(head); 94 rcu_lock_release(&rcu_callback_map); 95 return false; 96 } 97 98 /* Invoke the RCU callbacks whose grace period has elapsed. */ 99 static __latent_entropy void rcu_process_callbacks(void) 100 { 101 struct rcu_head *next, *list; 102 unsigned long flags; 103 104 /* Move the ready-to-invoke callbacks to a local list. */ 105 local_irq_save(flags); 106 if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) { 107 /* No callbacks ready, so just leave. */ 108 local_irq_restore(flags); 109 return; 110 } 111 list = rcu_ctrlblk.rcucblist; 112 rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail; 113 *rcu_ctrlblk.donetail = NULL; 114 if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail) 115 rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist; 116 rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist; 117 local_irq_restore(flags); 118 119 /* Invoke the callbacks on the local list. */ 120 while (list) { 121 next = list->next; 122 prefetch(next); 123 debug_rcu_head_unqueue(list); 124 rcu_reclaim_tiny(list); 125 list = next; 126 } 127 } 128 129 /* 130 * Wait for a grace period to elapse. But it is illegal to invoke 131 * synchronize_rcu() from within an RCU read-side critical section. 132 * Therefore, any legal call to synchronize_rcu() is a quiescent state, 133 * and so on a UP system, synchronize_rcu() need do nothing, other than 134 * let the polled APIs know that another grace period elapsed. 135 * 136 * (But Lai Jiangshan points out the benefits of doing might_sleep() 137 * to reduce latency.) 138 * 139 * Cool, huh? (Due to Josh Triplett.) 140 */ 141 void synchronize_rcu(void) 142 { 143 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || 144 lock_is_held(&rcu_lock_map) || 145 lock_is_held(&rcu_sched_lock_map), 146 "Illegal synchronize_rcu() in RCU read-side critical section"); 147 preempt_disable(); 148 WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2); 149 preempt_enable(); 150 } 151 EXPORT_SYMBOL_GPL(synchronize_rcu); 152 153 /* 154 * Post an RCU callback to be invoked after the end of an RCU grace 155 * period. But since we have but one CPU, that would be after any 156 * quiescent state. 157 */ 158 void call_rcu(struct rcu_head *head, rcu_callback_t func) 159 { 160 static atomic_t doublefrees; 161 unsigned long flags; 162 163 if (debug_rcu_head_queue(head)) { 164 if (atomic_inc_return(&doublefrees) < 4) { 165 pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func); 166 mem_dump_obj(head); 167 } 168 return; 169 } 170 171 head->func = func; 172 head->next = NULL; 173 174 local_irq_save(flags); 175 *rcu_ctrlblk.curtail = head; 176 rcu_ctrlblk.curtail = &head->next; 177 local_irq_restore(flags); 178 179 if (unlikely(is_idle_task(current))) { 180 /* force scheduling for rcu_qs() */ 181 resched_cpu(0); 182 } 183 } 184 EXPORT_SYMBOL_GPL(call_rcu); 185 186 /* 187 * Store a grace-period-counter "cookie". For more information, 188 * see the Tree RCU header comment. 189 */ 190 void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) 191 { 192 rgosp->rgos_norm = RCU_GET_STATE_COMPLETED; 193 } 194 EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full); 195 196 /* 197 * Return a grace-period-counter "cookie". For more information, 198 * see the Tree RCU header comment. 199 */ 200 unsigned long get_state_synchronize_rcu(void) 201 { 202 return READ_ONCE(rcu_ctrlblk.gp_seq); 203 } 204 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu); 205 206 /* 207 * Return a grace-period-counter "cookie" and ensure that a future grace 208 * period completes. For more information, see the Tree RCU header comment. 209 */ 210 unsigned long start_poll_synchronize_rcu(void) 211 { 212 unsigned long gp_seq = get_state_synchronize_rcu(); 213 214 if (unlikely(is_idle_task(current))) { 215 /* force scheduling for rcu_qs() */ 216 resched_cpu(0); 217 } 218 return gp_seq; 219 } 220 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu); 221 222 /* 223 * Return true if the grace period corresponding to oldstate has completed 224 * and false otherwise. For more information, see the Tree RCU header 225 * comment. 226 */ 227 bool poll_state_synchronize_rcu(unsigned long oldstate) 228 { 229 return oldstate == RCU_GET_STATE_COMPLETED || READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate; 230 } 231 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu); 232 233 #if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) 234 unsigned long long rcutorture_gather_gp_seqs(void) 235 { 236 return READ_ONCE(rcu_ctrlblk.gp_seq) & 0xffffULL; 237 } 238 EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs); 239 240 void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len) 241 { 242 snprintf(cp, len, "g%04llx", seqs & 0xffffULL); 243 } 244 EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs); 245 #endif 246 247 void __init rcu_init(void) 248 { 249 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); 250 rcu_early_boot_tests(); 251 tasks_cblist_init_generic(); 252 } 253