kernel/rcu/update.c

   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 */