1 /* 2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition. 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2 of the License, or 7 * (at your option) any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; if not, you can access it online at 16 * http://www.gnu.org/licenses/gpl-2.0.html. 17 * 18 * Copyright IBM Corporation, 2008 19 * 20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> 21 * 22 * For detailed explanation of Read-Copy Update mechanism see - 23 * Documentation/RCU 24 */ 25 #include <linux/completion.h> 26 #include <linux/interrupt.h> 27 #include <linux/notifier.h> 28 #include <linux/rcupdate.h> 29 #include <linux/kernel.h> 30 #include <linux/export.h> 31 #include <linux/mutex.h> 32 #include <linux/sched.h> 33 #include <linux/types.h> 34 #include <linux/init.h> 35 #include <linux/time.h> 36 #include <linux/cpu.h> 37 #include <linux/prefetch.h> 38 #include <linux/trace_events.h> 39 40 #include "rcu.h" 41 42 /* Forward declarations for tiny_plugin.h. */ 43 struct rcu_ctrlblk; 44 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp); 45 static void rcu_process_callbacks(struct softirq_action *unused); 46 static void __call_rcu(struct rcu_head *head, 47 void (*func)(struct rcu_head *rcu), 48 struct rcu_ctrlblk *rcp); 49 50 #include "tiny_plugin.h" 51 52 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) 53 54 /* 55 * Test whether RCU thinks that the current CPU is idle. 56 */ 57 bool notrace __rcu_is_watching(void) 58 { 59 return true; 60 } 61 EXPORT_SYMBOL(__rcu_is_watching); 62 63 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ 64 65 /* 66 * Helper function for rcu_sched_qs() and rcu_bh_qs(). 67 * Also irqs are disabled to avoid confusion due to interrupt handlers 68 * invoking call_rcu(). 69 */ 70 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) 71 { 72 RCU_TRACE(reset_cpu_stall_ticks(rcp)); 73 if (rcp->donetail != rcp->curtail) { 74 rcp->donetail = rcp->curtail; 75 return 1; 76 } 77 78 return 0; 79 } 80 81 /* 82 * Record an rcu quiescent state. And an rcu_bh quiescent state while we 83 * are at it, given that any rcu quiescent state is also an rcu_bh 84 * quiescent state. Use "+" instead of "||" to defeat short circuiting. 85 */ 86 void rcu_sched_qs(void) 87 { 88 unsigned long flags; 89 90 local_irq_save(flags); 91 if (rcu_qsctr_help(&rcu_sched_ctrlblk) + 92 rcu_qsctr_help(&rcu_bh_ctrlblk)) 93 raise_softirq(RCU_SOFTIRQ); 94 local_irq_restore(flags); 95 } 96 97 /* 98 * Record an rcu_bh quiescent state. 99 */ 100 void rcu_bh_qs(void) 101 { 102 unsigned long flags; 103 104 local_irq_save(flags); 105 if (rcu_qsctr_help(&rcu_bh_ctrlblk)) 106 raise_softirq(RCU_SOFTIRQ); 107 local_irq_restore(flags); 108 } 109 110 /* 111 * Check to see if the scheduling-clock interrupt came from an extended 112 * quiescent state, and, if so, tell RCU about it. This function must 113 * be called from hardirq context. It is normally called from the 114 * scheduling-clock interrupt. 115 */ 116 void rcu_check_callbacks(int user) 117 { 118 RCU_TRACE(check_cpu_stalls()); 119 if (user) 120 rcu_sched_qs(); 121 else if (!in_softirq()) 122 rcu_bh_qs(); 123 if (user) 124 rcu_note_voluntary_context_switch(current); 125 } 126 127 /* 128 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure 129 * whose grace period has elapsed. 130 */ 131 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) 132 { 133 const char *rn = NULL; 134 struct rcu_head *next, *list; 135 unsigned long flags; 136 RCU_TRACE(int cb_count = 0); 137 138 /* Move the ready-to-invoke callbacks to a local list. */ 139 local_irq_save(flags); 140 if (rcp->donetail == &rcp->rcucblist) { 141 /* No callbacks ready, so just leave. */ 142 local_irq_restore(flags); 143 return; 144 } 145 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); 146 list = rcp->rcucblist; 147 rcp->rcucblist = *rcp->donetail; 148 *rcp->donetail = NULL; 149 if (rcp->curtail == rcp->donetail) 150 rcp->curtail = &rcp->rcucblist; 151 rcp->donetail = &rcp->rcucblist; 152 local_irq_restore(flags); 153 154 /* Invoke the callbacks on the local list. */ 155 RCU_TRACE(rn = rcp->name); 156 while (list) { 157 next = list->next; 158 prefetch(next); 159 debug_rcu_head_unqueue(list); 160 local_bh_disable(); 161 __rcu_reclaim(rn, list); 162 local_bh_enable(); 163 list = next; 164 RCU_TRACE(cb_count++); 165 } 166 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); 167 RCU_TRACE(trace_rcu_batch_end(rcp->name, 168 cb_count, 0, need_resched(), 169 is_idle_task(current), 170 false)); 171 } 172 173 static void rcu_process_callbacks(struct softirq_action *unused) 174 { 175 __rcu_process_callbacks(&rcu_sched_ctrlblk); 176 __rcu_process_callbacks(&rcu_bh_ctrlblk); 177 } 178 179 /* 180 * Wait for a grace period to elapse. But it is illegal to invoke 181 * synchronize_sched() from within an RCU read-side critical section. 182 * Therefore, any legal call to synchronize_sched() is a quiescent 183 * state, and so on a UP system, synchronize_sched() need do nothing. 184 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the 185 * benefits of doing might_sleep() to reduce latency.) 186 * 187 * Cool, huh? (Due to Josh Triplett.) 188 * 189 * But we want to make this a static inline later. The cond_resched() 190 * currently makes this problematic. 191 */ 192 void synchronize_sched(void) 193 { 194 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || 195 lock_is_held(&rcu_lock_map) || 196 lock_is_held(&rcu_sched_lock_map), 197 "Illegal synchronize_sched() in RCU read-side critical section"); 198 cond_resched(); 199 } 200 EXPORT_SYMBOL_GPL(synchronize_sched); 201 202 /* 203 * Helper function for call_rcu() and call_rcu_bh(). 204 */ 205 static void __call_rcu(struct rcu_head *head, 206 void (*func)(struct rcu_head *rcu), 207 struct rcu_ctrlblk *rcp) 208 { 209 unsigned long flags; 210 211 debug_rcu_head_queue(head); 212 head->func = func; 213 head->next = NULL; 214 215 local_irq_save(flags); 216 *rcp->curtail = head; 217 rcp->curtail = &head->next; 218 RCU_TRACE(rcp->qlen++); 219 local_irq_restore(flags); 220 221 if (unlikely(is_idle_task(current))) { 222 /* force scheduling for rcu_sched_qs() */ 223 resched_cpu(0); 224 } 225 } 226 227 /* 228 * Post an RCU callback to be invoked after the end of an RCU-sched grace 229 * period. But since we have but one CPU, that would be after any 230 * quiescent state. 231 */ 232 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 233 { 234 __call_rcu(head, func, &rcu_sched_ctrlblk); 235 } 236 EXPORT_SYMBOL_GPL(call_rcu_sched); 237 238 /* 239 * Post an RCU bottom-half callback to be invoked after any subsequent 240 * quiescent state. 241 */ 242 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 243 { 244 __call_rcu(head, func, &rcu_bh_ctrlblk); 245 } 246 EXPORT_SYMBOL_GPL(call_rcu_bh); 247 248 void __init rcu_init(void) 249 { 250 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); 251 RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk)); 252 RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk)); 253 254 rcu_early_boot_tests(); 255 } 256