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 #ifdef CONFIG_PROVE_RCU_DELAY
  94                 udelay(10); /* Make preemption more probable. */
  95 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
  96                 barrier();  /* assign before ->rcu_read_unlock_special load */
  97                 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
  98                         rcu_read_unlock_special(t);
  99                 barrier();  /* ->rcu_read_unlock_special load before assign */
 100                 t->rcu_read_lock_nesting = 0;
 101         }
 102 #ifdef CONFIG_PROVE_LOCKING
 103         {
 104                 int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
 105
 106                 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
 107         }
 108 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 109 }
 110 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 111
 112 #endif /* #ifdef CONFIG_PREEMPT_RCU */
 113
 114 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 115 static struct lock_class_key rcu_lock_key;
 116 struct lockdep_map rcu_lock_map =
 117         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
 118 EXPORT_SYMBOL_GPL(rcu_lock_map);
 119
 120 static struct lock_class_key rcu_bh_lock_key;
 121 struct lockdep_map rcu_bh_lock_map =
 122         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
 123 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
 124
 125 static struct lock_class_key rcu_sched_lock_key;
 126 struct lockdep_map rcu_sched_lock_map =
 127         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 128 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 129
 130 static struct lock_class_key rcu_callback_key;
 131 struct lockdep_map rcu_callback_map =
 132         STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
 133 EXPORT_SYMBOL_GPL(rcu_callback_map);
 134
 135 int notrace debug_lockdep_rcu_enabled(void)
 136 {
 137         return rcu_scheduler_active && debug_locks &&
 138                current->lockdep_recursion == 0;
 139 }
 140 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 141
 142 /**
 143  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 144  *
 145  * Check for bottom half being disabled, which covers both the
 146  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 147  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 148  * will show the situation.  This is useful for debug checks in functions
 149  * that require that they be called within an RCU read-side critical
 150  * section.
 151  *
 152  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 153  *
 154  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 155  * offline from an RCU perspective, so check for those as well.
 156  */
 157 int rcu_read_lock_bh_held(void)
 158 {
 159         if (!debug_lockdep_rcu_enabled())
 160                 return 1;
 161         if (!rcu_is_watching())
 162                 return 0;
 163         if (!rcu_lockdep_current_cpu_online())
 164                 return 0;
 165         return in_softirq() || irqs_disabled();
 166 }
 167 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 168
 169 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 170
 171 struct rcu_synchronize {
 172         struct rcu_head head;
 173         struct completion completion;
 174 };
 175
 176 /*
 177  * Awaken the corresponding synchronize_rcu() instance now that a
 178  * grace period has elapsed.
 179  */
 180 static void wakeme_after_rcu(struct rcu_head  *head)
 181 {
 182         struct rcu_synchronize *rcu;
 183
 184         rcu = container_of(head, struct rcu_synchronize, head);
 185         complete(&rcu->completion);
 186 }
 187
 188 void wait_rcu_gp(call_rcu_func_t crf)
 189 {
 190         struct rcu_synchronize rcu;
 191
 192         init_rcu_head_on_stack(&rcu.head);
 193         init_completion(&rcu.completion);
 194         /* Will wake me after RCU finished. */
 195         crf(&rcu.head, wakeme_after_rcu);
 196         /* Wait for it. */
 197         wait_for_completion(&rcu.completion);
 198         destroy_rcu_head_on_stack(&rcu.head);
 199 }
 200 EXPORT_SYMBOL_GPL(wait_rcu_gp);
 201
 202 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 203 void init_rcu_head(struct rcu_head *head)
 204 {
 205         debug_object_init(head, &rcuhead_debug_descr);
 206 }
 207
 208 void destroy_rcu_head(struct rcu_head *head)
 209 {
 210         debug_object_free(head, &rcuhead_debug_descr);
 211 }
 212
 213 /*
 214  * fixup_activate is called when:
 215  * - an active object is activated
 216  * - an unknown object is activated (might be a statically initialized object)
 217  * Activation is performed internally by call_rcu().
 218  */
 219 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 220 {
 221         struct rcu_head *head = addr;
 222
 223         switch (state) {
 224
 225         case ODEBUG_STATE_NOTAVAILABLE:
 226                 /*
 227                  * This is not really a fixup. We just make sure that it is
 228                  * tracked in the object tracker.
 229                  */
 230                 debug_object_init(head, &rcuhead_debug_descr);
 231                 debug_object_activate(head, &rcuhead_debug_descr);
 232                 return 0;
 233         default:
 234                 return 1;
 235         }
 236 }
 237
 238 /**
 239  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 240  * @head: pointer to rcu_head structure to be initialized
 241  *
 242  * This function informs debugobjects of a new rcu_head structure that
 243  * has been allocated as an auto variable on the stack.  This function
 244  * is not required for rcu_head structures that are statically defined or
 245  * that are dynamically allocated on the heap.  This function has no
 246  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 247  */
 248 void init_rcu_head_on_stack(struct rcu_head *head)
 249 {
 250         debug_object_init_on_stack(head, &rcuhead_debug_descr);
 251 }
 252 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 253
 254 /**
 255  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 256  * @head: pointer to rcu_head structure to be initialized
 257  *
 258  * This function informs debugobjects that an on-stack rcu_head structure
 259  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 260  * function is not required for rcu_head structures that are statically
 261  * defined or that are dynamically allocated on the heap.  Also as with
 262  * init_rcu_head_on_stack(), this function has no effect for
 263  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 264  */
 265 void destroy_rcu_head_on_stack(struct rcu_head *head)
 266 {
 267         debug_object_free(head, &rcuhead_debug_descr);
 268 }
 269 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 270
 271 struct debug_obj_descr rcuhead_debug_descr = {
 272         .name = "rcu_head",
 273         .fixup_activate = rcuhead_fixup_activate,
 274 };
 275 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 276 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 277
 278 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 279 void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
 280                                unsigned long secs,
 281                                unsigned long c_old, unsigned long c)
 282 {
 283         trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
 284 }
 285 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 286 #else
 287 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
 288         do { } while (0)
 289 #endif
 290
 291 #ifdef CONFIG_RCU_STALL_COMMON
 292
 293 #ifdef CONFIG_PROVE_RCU
 294 #define RCU_STALL_DELAY_DELTA          (5 * HZ)
 295 #else
 296 #define RCU_STALL_DELAY_DELTA          0
 297 #endif
 298
 299 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
 300 static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
 301
 302 module_param(rcu_cpu_stall_suppress, int, 0644);
 303 module_param(rcu_cpu_stall_timeout, int, 0644);
 304
 305 int rcu_jiffies_till_stall_check(void)
 306 {
 307         int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
 308
 309         /*
 310          * Limit check must be consistent with the Kconfig limits
 311          * for CONFIG_RCU_CPU_STALL_TIMEOUT.
 312          */
 313         if (till_stall_check < 3) {
 314                 ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
 315                 till_stall_check = 3;
 316         } else if (till_stall_check > 300) {
 317                 ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
 318                 till_stall_check = 300;
 319         }
 320         return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
 321 }
 322
 323 void rcu_sysrq_start(void)
 324 {
 325         if (!rcu_cpu_stall_suppress)
 326                 rcu_cpu_stall_suppress = 2;
 327 }
 328
 329 void rcu_sysrq_end(void)
 330 {
 331         if (rcu_cpu_stall_suppress == 2)
 332                 rcu_cpu_stall_suppress = 0;
 333 }
 334
 335 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
 336 {
 337         rcu_cpu_stall_suppress = 1;
 338         return NOTIFY_DONE;
 339 }
 340
 341 static struct notifier_block rcu_panic_block = {
 342         .notifier_call = rcu_panic,
 343 };
 344
 345 static int __init check_cpu_stall_init(void)
 346 {
 347         atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
 348         return 0;
 349 }
 350 early_initcall(check_cpu_stall_init);
 351
 352 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */