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