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, write to the Free Software 16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. 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 #include <trace/events/rcu.h> 53 54 #include "rcu.h" 55 56 MODULE_ALIAS("rcupdate"); 57 #ifdef MODULE_PARAM_PREFIX 58 #undef MODULE_PARAM_PREFIX 59 #endif 60 #define MODULE_PARAM_PREFIX "rcupdate." 61 62 module_param(rcu_expedited, int, 0); 63 64 #ifdef CONFIG_PREEMPT_RCU 65 66 /* 67 * Preemptible RCU implementation for rcu_read_lock(). 68 * Just increment ->rcu_read_lock_nesting, shared state will be updated 69 * if we block. 70 */ 71 void __rcu_read_lock(void) 72 { 73 current->rcu_read_lock_nesting++; 74 barrier(); /* critical section after entry code. */ 75 } 76 EXPORT_SYMBOL_GPL(__rcu_read_lock); 77 78 /* 79 * Preemptible RCU implementation for rcu_read_unlock(). 80 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost 81 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then 82 * invoke rcu_read_unlock_special() to clean up after a context switch 83 * in an RCU read-side critical section and other special cases. 84 */ 85 void __rcu_read_unlock(void) 86 { 87 struct task_struct *t = current; 88 89 if (t->rcu_read_lock_nesting != 1) { 90 --t->rcu_read_lock_nesting; 91 } else { 92 barrier(); /* critical section before exit code. */ 93 t->rcu_read_lock_nesting = INT_MIN; 94 #ifdef CONFIG_PROVE_RCU_DELAY 95 udelay(10); /* Make preemption more probable. */ 96 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ 97 barrier(); /* assign before ->rcu_read_unlock_special load */ 98 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) 99 rcu_read_unlock_special(t); 100 barrier(); /* ->rcu_read_unlock_special load before assign */ 101 t->rcu_read_lock_nesting = 0; 102 } 103 #ifdef CONFIG_PROVE_LOCKING 104 { 105 int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); 106 107 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); 108 } 109 #endif /* #ifdef CONFIG_PROVE_LOCKING */ 110 } 111 EXPORT_SYMBOL_GPL(__rcu_read_unlock); 112 113 #endif /* #ifdef CONFIG_PREEMPT_RCU */ 114 115 #ifdef CONFIG_DEBUG_LOCK_ALLOC 116 static struct lock_class_key rcu_lock_key; 117 struct lockdep_map rcu_lock_map = 118 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); 119 EXPORT_SYMBOL_GPL(rcu_lock_map); 120 121 static struct lock_class_key rcu_bh_lock_key; 122 struct lockdep_map rcu_bh_lock_map = 123 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key); 124 EXPORT_SYMBOL_GPL(rcu_bh_lock_map); 125 126 static struct lock_class_key rcu_sched_lock_key; 127 struct lockdep_map rcu_sched_lock_map = 128 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key); 129 EXPORT_SYMBOL_GPL(rcu_sched_lock_map); 130 131 static struct lock_class_key rcu_callback_key; 132 struct lockdep_map rcu_callback_map = 133 STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key); 134 EXPORT_SYMBOL_GPL(rcu_callback_map); 135 136 int notrace debug_lockdep_rcu_enabled(void) 137 { 138 return rcu_scheduler_active && debug_locks && 139 current->lockdep_recursion == 0; 140 } 141 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); 142 143 /** 144 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section? 145 * 146 * Check for bottom half being disabled, which covers both the 147 * CONFIG_PROVE_RCU and not cases. Note that if someone uses 148 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled) 149 * will show the situation. This is useful for debug checks in functions 150 * that require that they be called within an RCU read-side critical 151 * section. 152 * 153 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot. 154 * 155 * Note that rcu_read_lock() is disallowed if the CPU is either idle or 156 * offline from an RCU perspective, so check for those as well. 157 */ 158 int rcu_read_lock_bh_held(void) 159 { 160 if (!debug_lockdep_rcu_enabled()) 161 return 1; 162 if (!rcu_is_watching()) 163 return 0; 164 if (!rcu_lockdep_current_cpu_online()) 165 return 0; 166 return in_softirq() || irqs_disabled(); 167 } 168 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held); 169 170 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 171 172 struct rcu_synchronize { 173 struct rcu_head head; 174 struct completion completion; 175 }; 176 177 /* 178 * Awaken the corresponding synchronize_rcu() instance now that a 179 * grace period has elapsed. 180 */ 181 static void wakeme_after_rcu(struct rcu_head *head) 182 { 183 struct rcu_synchronize *rcu; 184 185 rcu = container_of(head, struct rcu_synchronize, head); 186 complete(&rcu->completion); 187 } 188 189 void wait_rcu_gp(call_rcu_func_t crf) 190 { 191 struct rcu_synchronize rcu; 192 193 init_rcu_head_on_stack(&rcu.head); 194 init_completion(&rcu.completion); 195 /* Will wake me after RCU finished. */ 196 crf(&rcu.head, wakeme_after_rcu); 197 /* Wait for it. */ 198 wait_for_completion(&rcu.completion); 199 destroy_rcu_head_on_stack(&rcu.head); 200 } 201 EXPORT_SYMBOL_GPL(wait_rcu_gp); 202 203 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD 204 static inline void debug_init_rcu_head(struct rcu_head *head) 205 { 206 debug_object_init(head, &rcuhead_debug_descr); 207 } 208 209 static inline void debug_rcu_head_free(struct rcu_head *head) 210 { 211 debug_object_free(head, &rcuhead_debug_descr); 212 } 213 214 /* 215 * fixup_activate is called when: 216 * - an active object is activated 217 * - an unknown object is activated (might be a statically initialized object) 218 * Activation is performed internally by call_rcu(). 219 */ 220 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state) 221 { 222 struct rcu_head *head = addr; 223 224 switch (state) { 225 226 case ODEBUG_STATE_NOTAVAILABLE: 227 /* 228 * This is not really a fixup. We just make sure that it is 229 * tracked in the object tracker. 230 */ 231 debug_object_init(head, &rcuhead_debug_descr); 232 debug_object_activate(head, &rcuhead_debug_descr); 233 return 0; 234 default: 235 return 1; 236 } 237 } 238 239 /** 240 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects 241 * @head: pointer to rcu_head structure to be initialized 242 * 243 * This function informs debugobjects of a new rcu_head structure that 244 * has been allocated as an auto variable on the stack. This function 245 * is not required for rcu_head structures that are statically defined or 246 * that are dynamically allocated on the heap. This function has no 247 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. 248 */ 249 void init_rcu_head_on_stack(struct rcu_head *head) 250 { 251 debug_object_init_on_stack(head, &rcuhead_debug_descr); 252 } 253 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack); 254 255 /** 256 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects 257 * @head: pointer to rcu_head structure to be initialized 258 * 259 * This function informs debugobjects that an on-stack rcu_head structure 260 * is about to go out of scope. As with init_rcu_head_on_stack(), this 261 * function is not required for rcu_head structures that are statically 262 * defined or that are dynamically allocated on the heap. Also as with 263 * init_rcu_head_on_stack(), this function has no effect for 264 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds. 265 */ 266 void destroy_rcu_head_on_stack(struct rcu_head *head) 267 { 268 debug_object_free(head, &rcuhead_debug_descr); 269 } 270 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack); 271 272 struct debug_obj_descr rcuhead_debug_descr = { 273 .name = "rcu_head", 274 .fixup_activate = rcuhead_fixup_activate, 275 }; 276 EXPORT_SYMBOL_GPL(rcuhead_debug_descr); 277 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ 278 279 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE) 280 void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp, 281 unsigned long secs, 282 unsigned long c_old, unsigned long c) 283 { 284 trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c); 285 } 286 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); 287 #else 288 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \ 289 do { } while (0) 290 #endif 291 292 #ifdef CONFIG_RCU_STALL_COMMON 293 294 #ifdef CONFIG_PROVE_RCU 295 #define RCU_STALL_DELAY_DELTA (5 * HZ) 296 #else 297 #define RCU_STALL_DELAY_DELTA 0 298 #endif 299 300 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ 301 static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; 302 303 module_param(rcu_cpu_stall_suppress, int, 0644); 304 module_param(rcu_cpu_stall_timeout, int, 0644); 305 306 int rcu_jiffies_till_stall_check(void) 307 { 308 int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout); 309 310 /* 311 * Limit check must be consistent with the Kconfig limits 312 * for CONFIG_RCU_CPU_STALL_TIMEOUT. 313 */ 314 if (till_stall_check < 3) { 315 ACCESS_ONCE(rcu_cpu_stall_timeout) = 3; 316 till_stall_check = 3; 317 } else if (till_stall_check > 300) { 318 ACCESS_ONCE(rcu_cpu_stall_timeout) = 300; 319 till_stall_check = 300; 320 } 321 return till_stall_check * HZ + RCU_STALL_DELAY_DELTA; 322 } 323 324 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr) 325 { 326 rcu_cpu_stall_suppress = 1; 327 return NOTIFY_DONE; 328 } 329 330 static struct notifier_block rcu_panic_block = { 331 .notifier_call = rcu_panic, 332 }; 333 334 static int __init check_cpu_stall_init(void) 335 { 336 atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block); 337 return 0; 338 } 339 early_initcall(check_cpu_stall_init); 340 341 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ 342