1 /* 2 * Read-Copy Update mechanism for mutual exclusion 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, 2001 19 * 20 * Authors: Dipankar Sarma <dipankar@in.ibm.com> 21 * Manfred Spraul <manfred@colorfullife.com> 22 * 23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com> 24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. 25 * Papers: 26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf 27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) 28 * 29 * For detailed explanation of Read-Copy Update mechanism see - 30 * http://lse.sourceforge.net/locking/rcupdate.html 31 * 32 */ 33 #include <linux/types.h> 34 #include <linux/kernel.h> 35 #include <linux/init.h> 36 #include <linux/spinlock.h> 37 #include <linux/smp.h> 38 #include <linux/interrupt.h> 39 #include <linux/sched.h> 40 #include <linux/atomic.h> 41 #include <linux/bitops.h> 42 #include <linux/percpu.h> 43 #include <linux/notifier.h> 44 #include <linux/cpu.h> 45 #include <linux/mutex.h> 46 #include <linux/export.h> 47 #include <linux/hardirq.h> 48 #include <linux/delay.h> 49 #include <linux/module.h> 50 51 #define CREATE_TRACE_POINTS 52 53 #include "rcu.h" 54 55 MODULE_ALIAS("rcupdate"); 56 #ifdef MODULE_PARAM_PREFIX 57 #undef MODULE_PARAM_PREFIX 58 #endif 59 #define MODULE_PARAM_PREFIX "rcupdate." 60 61 module_param(rcu_expedited, int, 0); 62 63 #ifdef CONFIG_PREEMPT_RCU 64 65 /* 66 * Preemptible RCU implementation for rcu_read_lock(). 67 * Just increment ->rcu_read_lock_nesting, shared state will be updated 68 * if we block. 69 */ 70 void __rcu_read_lock(void) 71 { 72 current->rcu_read_lock_nesting++; 73 barrier(); /* critical section after entry code. */ 74 } 75 EXPORT_SYMBOL_GPL(__rcu_read_lock); 76 77 /* 78 * Preemptible RCU implementation for rcu_read_unlock(). 79 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost 80 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then 81 * invoke rcu_read_unlock_special() to clean up after a context switch 82 * in an RCU read-side critical section and other special cases. 83 */ 84 void __rcu_read_unlock(void) 85 { 86 struct task_struct *t = current; 87 88 if (t->rcu_read_lock_nesting != 1) { 89 --t->rcu_read_lock_nesting; 90 } else { 91 barrier(); /* critical section before exit code. */ 92 t->rcu_read_lock_nesting = INT_MIN; 93 barrier(); /* assign before ->rcu_read_unlock_special load */ 94 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) 95 rcu_read_unlock_special(t); 96 barrier(); /* ->rcu_read_unlock_special load before assign */ 97 t->rcu_read_lock_nesting = 0; 98 } 99 #ifdef CONFIG_PROVE_LOCKING 100 { 101 int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); 102 103 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); 104 } 105 #endif /* #ifdef CONFIG_PROVE_LOCKING */ 106 } 107 EXPORT_SYMBOL_GPL(__rcu_read_unlock); 108 109 #endif /* #ifdef CONFIG_PREEMPT_RCU */ 110 111 #ifdef CONFIG_DEBUG_LOCK_ALLOC 112 static struct lock_class_key rcu_lock_key; 113 struct lockdep_map rcu_lock_map = 114 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); 115 EXPORT_SYMBOL_GPL(rcu_lock_map); 116 117 static struct lock_class_key rcu_bh_lock_key; 118 struct lockdep_map rcu_bh_lock_map = 119 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); 120 EXPORT_SYMBOL_GPL(rcu_bh_lock_map); 121 122 static struct lock_class_key rcu_sched_lock_key; 123 struct lockdep_map rcu_sched_lock_map = 124 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); 125 EXPORT_SYMBOL_GPL(rcu_sched_lock_map); 126 127 static struct lock_class_key rcu_callback_key; 128 struct lockdep_map rcu_callback_map = 129 STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key); 130 EXPORT_SYMBOL_GPL(rcu_callback_map); 131 132 int notrace debug_lockdep_rcu_enabled(void) 133 { 134 return rcu_scheduler_active && debug_locks && 135 current->lockdep_recursion == 0; 136 } 137 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); 138 139 /** 140 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? 141 * 142 * Check for bottom half being disabled, which covers both the 143 * CONFIG_PROVE_RCU and not cases. Note that if someone uses 144 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) 145 * will show the situation. This is useful for debug checks in functions 146 * that require that they be called within an RCU read-side critical 147 * section. 148 * 149 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. 150 * 151 * Note that rcu_read_lock() is disallowed if the CPU is either idle or 152 * offline from an RCU perspective, so check for those as well. 153 */ 154 int rcu_read_lock_bh_held(void) 155 { 156 if (!debug_lockdep_rcu_enabled()) 157 return 1; 158 if (!rcu_is_watching()) 159 return 0; 160 if (!rcu_lockdep_current_cpu_online()) 161 return 0; 162 return in_softirq() || irqs_disabled(); 163 } 164 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); 165 166 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 167 168 struct rcu_synchronize { 169 struct rcu_head head; 170 struct completion completion; 171 }; 172 173 /* 174 * Awaken the corresponding synchronize_rcu() instance now that a 175 * grace period has elapsed. 176 */ 177 static void wakeme_after_rcu(struct rcu_head *head) 178 { 179 struct rcu_synchronize *rcu; 180 181 rcu = container_of(head, struct rcu_synchronize, head); 182 complete(&rcu->completion); 183 } 184 185 void wait_rcu_gp(call_rcu_func_t crf) 186 { 187 struct rcu_synchronize rcu; 188 189 init_rcu_head_on_stack(&rcu.head); 190 init_completion(&rcu.completion); 191 /* Will wake me after RCU finished. */ 192 crf(&rcu.head, wakeme_after_rcu); 193 /* Wait for it. */ 194 wait_for_completion(&rcu.completion); 195 destroy_rcu_head_on_stack(&rcu.head); 196 } 197 EXPORT_SYMBOL_GPL(wait_rcu_gp); 198 199 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 200 void init_rcu_head(struct rcu_head *head) 201 { 202 debug_object_init(head, &rcuhead_debug_descr); 203 } 204 205 void destroy_rcu_head(struct rcu_head *head) 206 { 207 debug_object_free(head, &rcuhead_debug_descr); 208 } 209 210 /* 211 * fixup_activate is called when: 212 * - an active object is activated 213 * - an unknown object is activated (might be a statically initialized object) 214 * Activation is performed internally by call_rcu(). 215 */ 216 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) 217 { 218 struct rcu_head *head = addr; 219 220 switch (state) { 221 222 case ODEBUG_STATE_NOTAVAILABLE: 223 /* 224 * This is not really a fixup. We just make sure that it is 225 * tracked in the object tracker. 226 */ 227 debug_object_init(head, &rcuhead_debug_descr); 228 debug_object_activate(head, &rcuhead_debug_descr); 229 return 0; 230 default: 231 return 1; 232 } 233 } 234 235 /** 236 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects 237 * @head: pointer to rcu_head structure to be initialized 238 * 239 * This function informs debugobjects of a new rcu_head structure that 240 * has been allocated as an auto variable on the stack. This function 241 * is not required for rcu_head structures that are statically defined or 242 * that are dynamically allocated on the heap. This function has no 243 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. 244 */ 245 void init_rcu_head_on_stack(struct rcu_head *head) 246 { 247 debug_object_init_on_stack(head, &rcuhead_debug_descr); 248 } 249 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); 250 251 /** 252 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects 253 * @head: pointer to rcu_head structure to be initialized 254 * 255 * This function informs debugobjects that an on-stack rcu_head structure 256 * is about to go out of scope. As with init_rcu_head_on_stack(), this 257 * function is not required for rcu_head structures that are statically 258 * defined or that are dynamically allocated on the heap. Also as with 259 * init_rcu_head_on_stack(), this function has no effect for 260 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. 261 */ 262 void destroy_rcu_head_on_stack(struct rcu_head *head) 263 { 264 debug_object_free(head, &rcuhead_debug_descr); 265 } 266 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); 267 268 struct debug_obj_descr rcuhead_debug_descr = { 269 .name = "rcu_head", 270 .fixup_activate = rcuhead_fixup_activate, 271 }; 272 EXPORT_SYMBOL_GPL(rcuhead_debug_descr); 273 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 274 275 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) 276 void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp, 277 unsigned long secs, 278 unsigned long c_old, unsigned long c) 279 { 280 trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c); 281 } 282 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); 283 #else 284 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ 285 do { } while (0) 286 #endif 287 288 #ifdef CONFIG_RCU_STALL_COMMON 289 290 #ifdef CONFIG_PROVE_RCU 291 #define RCU_STALL_DELAY_DELTA (5 * HZ) 292 #else 293 #define RCU_STALL_DELAY_DELTA 0 294 #endif 295 296 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ 297 static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; 298 299 module_param(rcu_cpu_stall_suppress, int, 0644); 300 module_param(rcu_cpu_stall_timeout, int, 0644); 301 302 int rcu_jiffies_till_stall_check(void) 303 { 304 int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); 305 306 /* 307 * Limit check must be consistent with the Kconfig limits 308 * for CONFIG_RCU_CPU_STALL_TIMEOUT. 309 */ 310 if (till_stall_check < 3) { 311 ACCESS_ONCE(rcu_cpu_stall_timeout) = 3; 312 till_stall_check = 3; 313 } else if (till_stall_check > 300) { 314 ACCESS_ONCE(rcu_cpu_stall_timeout) = 300; 315 till_stall_check = 300; 316 } 317 return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; 318 } 319 320 void rcu_sysrq_start(void) 321 { 322 if (!rcu_cpu_stall_suppress) 323 rcu_cpu_stall_suppress = 2; 324 } 325 326 void rcu_sysrq_end(void) 327 { 328 if (rcu_cpu_stall_suppress == 2) 329 rcu_cpu_stall_suppress = 0; 330 } 331 332 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) 333 { 334 rcu_cpu_stall_suppress = 1; 335 return NOTIFY_DONE; 336 } 337 338 static struct notifier_block rcu_panic_block = { 339 .notifier_call = rcu_panic, 340 }; 341 342 static int __init check_cpu_stall_init(void) 343 { 344 atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); 345 return 0; 346 } 347 early_initcall(check_cpu_stall_init); 348 349 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ 350