kernel/rcupdate.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_param(rcu_expedited, int, 0);
  57
  58 #ifdef CONFIG_PREEMPT_RCU
  59
  60 /*
  61  * Preemptible RCU implementation for rcu_read_lock().
  62  * Just increment ->rcu_read_lock_nesting, shared state will be updated
  63  * if we block.
  64  */
  65 void __rcu_read_lock(void)
  66 {
  67         current->rcu_read_lock_nesting++;
  68         barrier();  /* critical section after entry code. */
  69 }
  70 EXPORT_SYMBOL_GPL(__rcu_read_lock);
  71
  72 /*
  73  * Preemptible RCU implementation for rcu_read_unlock().
  74  * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
  75  * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
  76  * invoke rcu_read_unlock_special() to clean up after a context switch
  77  * in an RCU read-side critical section and other special cases.
  78  */
  79 void __rcu_read_unlock(void)
  80 {
  81         struct task_struct *t = current;
  82
  83         if (t->rcu_read_lock_nesting != 1) {
  84                 --t->rcu_read_lock_nesting;
  85         } else {
  86                 barrier();  /* critical section before exit code. */
  87                 t->rcu_read_lock_nesting = INT_MIN;
  88 #ifdef CONFIG_PROVE_RCU_DELAY
  89                 udelay(10); /* Make preemption more probable. */
  90 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
  91                 barrier();  /* assign before ->rcu_read_unlock_special load */
  92                 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
  93                         rcu_read_unlock_special(t);
  94                 barrier();  /* ->rcu_read_unlock_special load before assign */
  95                 t->rcu_read_lock_nesting = 0;
  96         }
  97 #ifdef CONFIG_PROVE_LOCKING
  98         {
  99                 int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
 100
 101                 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
 102         }
 103 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 104 }
 105 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 106
 107 #endif /* #ifdef CONFIG_PREEMPT_RCU */
 108
 109 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 110 static struct lock_class_key rcu_lock_key;
 111 struct lockdep_map rcu_lock_map =
 112         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
 113 EXPORT_SYMBOL_GPL(rcu_lock_map);
 114
 115 static struct lock_class_key rcu_bh_lock_key;
 116 struct lockdep_map rcu_bh_lock_map =
 117         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
 118 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
 119
 120 static struct lock_class_key rcu_sched_lock_key;
 121 struct lockdep_map rcu_sched_lock_map =
 122         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 123 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 124
 125 int notrace debug_lockdep_rcu_enabled(void)
 126 {
 127         return rcu_scheduler_active && debug_locks &&
 128                current->lockdep_recursion == 0;
 129 }
 130 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 131
 132 /**
 133  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 134  *
 135  * Check for bottom half being disabled, which covers both the
 136  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 137  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 138  * will show the situation.  This is useful for debug checks in functions
 139  * that require that they be called within an RCU read-side critical
 140  * section.
 141  *
 142  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 143  *
 144  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 145  * offline from an RCU perspective, so check for those as well.
 146  */
 147 int rcu_read_lock_bh_held(void)
 148 {
 149         if (!debug_lockdep_rcu_enabled())
 150                 return 1;
 151         if (rcu_is_cpu_idle())
 152                 return 0;
 153         if (!rcu_lockdep_current_cpu_online())
 154                 return 0;
 155         return in_softirq() || irqs_disabled();
 156 }
 157 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 158
 159 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 160
 161 struct rcu_synchronize {
 162         struct rcu_head head;
 163         struct completion completion;
 164 };
 165
 166 /*
 167  * Awaken the corresponding synchronize_rcu() instance now that a
 168  * grace period has elapsed.
 169  */
 170 static void wakeme_after_rcu(struct rcu_head  *head)
 171 {
 172         struct rcu_synchronize *rcu;
 173
 174         rcu = container_of(head, struct rcu_synchronize, head);
 175         complete(&rcu->completion);
 176 }
 177
 178 void wait_rcu_gp(call_rcu_func_t crf)
 179 {
 180         struct rcu_synchronize rcu;
 181
 182         init_rcu_head_on_stack(&rcu.head);
 183         init_completion(&rcu.completion);
 184         /* Will wake me after RCU finished. */
 185         crf(&rcu.head, wakeme_after_rcu);
 186         /* Wait for it. */
 187         wait_for_completion(&rcu.completion);
 188         destroy_rcu_head_on_stack(&rcu.head);
 189 }
 190 EXPORT_SYMBOL_GPL(wait_rcu_gp);
 191
 192 #ifdef CONFIG_PROVE_RCU
 193 /*
 194  * wrapper function to avoid #include problems.
 195  */
 196 int rcu_my_thread_group_empty(void)
 197 {
 198         return thread_group_empty(current);
 199 }
 200 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 201 #endif /* #ifdef CONFIG_PROVE_RCU */
 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 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 */