kernel/rcutiny.c

   1 /*
   2  * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
   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, 2008
  19  *
  20  * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  21  *
  22  * For detailed explanation of Read-Copy Update mechanism see -
  23  *              Documentation/RCU
  24  */
  25 #include <linux/moduleparam.h>
  26 #include <linux/completion.h>
  27 #include <linux/interrupt.h>
  28 #include <linux/notifier.h>
  29 #include <linux/rcupdate.h>
  30 #include <linux/kernel.h>
  31 #include <linux/module.h>
  32 #include <linux/mutex.h>
  33 #include <linux/sched.h>
  34 #include <linux/types.h>
  35 #include <linux/init.h>
  36 #include <linux/time.h>
  37 #include <linux/cpu.h>
  38
  39 /* Global control variables for rcupdate callback mechanism. */
  40 struct rcu_ctrlblk {
  41         struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
  42         struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
  43         struct rcu_head **curtail;      /* ->next pointer of last CB. */
  44 };
  45
  46 /* Definition for rcupdate control block. */
  47 static struct rcu_ctrlblk rcu_sched_ctrlblk = {
  48         .donetail       = &rcu_sched_ctrlblk.rcucblist,
  49         .curtail        = &rcu_sched_ctrlblk.rcucblist,
  50 };
  51
  52 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
  53         .donetail       = &rcu_bh_ctrlblk.rcucblist,
  54         .curtail        = &rcu_bh_ctrlblk.rcucblist,
  55 };
  56
  57 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  58 int rcu_scheduler_active __read_mostly;
  59 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  60 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  61
  62 #ifdef CONFIG_NO_HZ
  63
  64 static long rcu_dynticks_nesting = 1;
  65
  66 /*
  67  * Enter dynticks-idle mode, which is an extended quiescent state
  68  * if we have fully entered that mode (i.e., if the new value of
  69  * dynticks_nesting is zero).
  70  */
  71 void rcu_enter_nohz(void)
  72 {
  73         if (--rcu_dynticks_nesting == 0)
  74                 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
  75 }
  76
  77 /*
  78  * Exit dynticks-idle mode, so that we are no longer in an extended
  79  * quiescent state.
  80  */
  81 void rcu_exit_nohz(void)
  82 {
  83         rcu_dynticks_nesting++;
  84 }
  85
  86 #endif /* #ifdef CONFIG_NO_HZ */
  87
  88 /*
  89  * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
  90  * Also disable irqs to avoid confusion due to interrupt handlers
  91  * invoking call_rcu().
  92  */
  93 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  94 {
  95         unsigned long flags;
  96
  97         local_irq_save(flags);
  98         if (rcp->rcucblist != NULL &&
  99             rcp->donetail != rcp->curtail) {
 100                 rcp->donetail = rcp->curtail;
 101                 local_irq_restore(flags);
 102                 return 1;
 103         }
 104         local_irq_restore(flags);
 105
 106         return 0;
 107 }
 108
 109 /*
 110  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 111  * are at it, given that any rcu quiescent state is also an rcu_bh
 112  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 113  */
 114 void rcu_sched_qs(int cpu)
 115 {
 116         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 117             rcu_qsctr_help(&rcu_bh_ctrlblk))
 118                 raise_softirq(RCU_SOFTIRQ);
 119 }
 120
 121 /*
 122  * Record an rcu_bh quiescent state.
 123  */
 124 void rcu_bh_qs(int cpu)
 125 {
 126         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 127                 raise_softirq(RCU_SOFTIRQ);
 128 }
 129
 130 /*
 131  * Check to see if the scheduling-clock interrupt came from an extended
 132  * quiescent state, and, if so, tell RCU about it.
 133  */
 134 void rcu_check_callbacks(int cpu, int user)
 135 {
 136         if (user ||
 137             (idle_cpu(cpu) &&
 138              !in_softirq() &&
 139              hardirq_count() <= (1 << HARDIRQ_SHIFT)))
 140                 rcu_sched_qs(cpu);
 141         else if (!in_softirq())
 142                 rcu_bh_qs(cpu);
 143 }
 144
 145 /*
 146  * Helper function for rcu_process_callbacks() that operates on the
 147  * specified rcu_ctrlkblk structure.
 148  */
 149 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 150 {
 151         struct rcu_head *next, *list;
 152         unsigned long flags;
 153
 154         /* If no RCU callbacks ready to invoke, just return. */
 155         if (&rcp->rcucblist == rcp->donetail)
 156                 return;
 157
 158         /* Move the ready-to-invoke callbacks to a local list. */
 159         local_irq_save(flags);
 160         list = rcp->rcucblist;
 161         rcp->rcucblist = *rcp->donetail;
 162         *rcp->donetail = NULL;
 163         if (rcp->curtail == rcp->donetail)
 164                 rcp->curtail = &rcp->rcucblist;
 165         rcp->donetail = &rcp->rcucblist;
 166         local_irq_restore(flags);
 167
 168         /* Invoke the callbacks on the local list. */
 169         while (list) {
 170                 next = list->next;
 171                 prefetch(next);
 172                 list->func(list);
 173                 list = next;
 174         }
 175 }
 176
 177 /*
 178  * Invoke any callbacks whose grace period has completed.
 179  */
 180 static void rcu_process_callbacks(struct softirq_action *unused)
 181 {
 182         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 183         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 184 }
 185
 186 /*
 187  * Wait for a grace period to elapse.  But it is illegal to invoke
 188  * synchronize_sched() from within an RCU read-side critical section.
 189  * Therefore, any legal call to synchronize_sched() is a quiescent
 190  * state, and so on a UP system, synchronize_sched() need do nothing.
 191  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 192  * benefits of doing might_sleep() to reduce latency.)
 193  *
 194  * Cool, huh?  (Due to Josh Triplett.)
 195  *
 196  * But we want to make this a static inline later.  The cond_resched()
 197  * currently makes this problematic.
 198  */
 199 void synchronize_sched(void)
 200 {
 201         cond_resched();
 202 }
 203 EXPORT_SYMBOL_GPL(synchronize_sched);
 204
 205 /*
 206  * Helper function for call_rcu() and call_rcu_bh().
 207  */
 208 static void __call_rcu(struct rcu_head *head,
 209                        void (*func)(struct rcu_head *rcu),
 210                        struct rcu_ctrlblk *rcp)
 211 {
 212         unsigned long flags;
 213
 214         head->func = func;
 215         head->next = NULL;
 216
 217         local_irq_save(flags);
 218         *rcp->curtail = head;
 219         rcp->curtail = &head->next;
 220         local_irq_restore(flags);
 221 }
 222
 223 /*
 224  * Post an RCU callback to be invoked after the end of an RCU grace
 225  * period.  But since we have but one CPU, that would be after any
 226  * quiescent state.
 227  */
 228 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 229 {
 230         __call_rcu(head, func, &rcu_sched_ctrlblk);
 231 }
 232 EXPORT_SYMBOL_GPL(call_rcu);
 233
 234 /*
 235  * Post an RCU bottom-half callback to be invoked after any subsequent
 236  * quiescent state.
 237  */
 238 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 239 {
 240         __call_rcu(head, func, &rcu_bh_ctrlblk);
 241 }
 242 EXPORT_SYMBOL_GPL(call_rcu_bh);
 243
 244 void rcu_barrier(void)
 245 {
 246         struct rcu_synchronize rcu;
 247
 248         init_rcu_head_on_stack(&rcu.head);
 249         init_completion(&rcu.completion);
 250         /* Will wake me after RCU finished. */
 251         call_rcu(&rcu.head, wakeme_after_rcu);
 252         /* Wait for it. */
 253         wait_for_completion(&rcu.completion);
 254         destroy_rcu_head_on_stack(&rcu.head);
 255 }
 256 EXPORT_SYMBOL_GPL(rcu_barrier);
 257
 258 void rcu_barrier_bh(void)
 259 {
 260         struct rcu_synchronize rcu;
 261
 262         init_rcu_head_on_stack(&rcu.head);
 263         init_completion(&rcu.completion);
 264         /* Will wake me after RCU finished. */
 265         call_rcu_bh(&rcu.head, wakeme_after_rcu);
 266         /* Wait for it. */
 267         wait_for_completion(&rcu.completion);
 268         destroy_rcu_head_on_stack(&rcu.head);
 269 }
 270 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
 271
 272 void rcu_barrier_sched(void)
 273 {
 274         struct rcu_synchronize rcu;
 275
 276         init_rcu_head_on_stack(&rcu.head);
 277         init_completion(&rcu.completion);
 278         /* Will wake me after RCU finished. */
 279         call_rcu_sched(&rcu.head, wakeme_after_rcu);
 280         /* Wait for it. */
 281         wait_for_completion(&rcu.completion);
 282         destroy_rcu_head_on_stack(&rcu.head);
 283 }
 284 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
 285
 286 void __init rcu_init(void)
 287 {
 288         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 289 }
 290
 291 #include "rcutiny_plugin.h"