kernel/rcu/tiny.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, you can access it online at
  16  * http://www.gnu.org/licenses/gpl-2.0.html.
  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/completion.h>
  26 #include <linux/interrupt.h>
  27 #include <linux/notifier.h>
  28 #include <linux/rcupdate_wait.h>
  29 #include <linux/kernel.h>
  30 #include <linux/export.h>
  31 #include <linux/mutex.h>
  32 #include <linux/sched.h>
  33 #include <linux/types.h>
  34 #include <linux/init.h>
  35 #include <linux/time.h>
  36 #include <linux/cpu.h>
  37 #include <linux/prefetch.h>
  38
  39 #include "rcu.h"
  40
  41 /* Global control variables for rcupdate callback mechanism. */
  42 struct rcu_ctrlblk {
  43         struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
  44         struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
  45         struct rcu_head **curtail;      /* ->next pointer of last CB. */
  46 };
  47
  48 /* Definition for rcupdate control block. */
  49 static struct rcu_ctrlblk rcu_sched_ctrlblk = {
  50         .donetail       = &rcu_sched_ctrlblk.rcucblist,
  51         .curtail        = &rcu_sched_ctrlblk.rcucblist,
  52 };
  53
  54 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
  55         .donetail       = &rcu_bh_ctrlblk.rcucblist,
  56         .curtail        = &rcu_bh_ctrlblk.rcucblist,
  57 };
  58
  59 void rcu_barrier_bh(void)
  60 {
  61         wait_rcu_gp(call_rcu_bh);
  62 }
  63 EXPORT_SYMBOL(rcu_barrier_bh);
  64
  65 void rcu_barrier_sched(void)
  66 {
  67         wait_rcu_gp(call_rcu_sched);
  68 }
  69 EXPORT_SYMBOL(rcu_barrier_sched);
  70
  71 /*
  72  * Helper function for rcu_sched_qs() and rcu_bh_qs().
  73  * Also irqs are disabled to avoid confusion due to interrupt handlers
  74  * invoking call_rcu().
  75  */
  76 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  77 {
  78         if (rcp->donetail != rcp->curtail) {
  79                 rcp->donetail = rcp->curtail;
  80                 return 1;
  81         }
  82
  83         return 0;
  84 }
  85
  86 /*
  87  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
  88  * are at it, given that any rcu quiescent state is also an rcu_bh
  89  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
  90  */
  91 void rcu_sched_qs(void)
  92 {
  93         unsigned long flags;
  94
  95         local_irq_save(flags);
  96         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
  97             rcu_qsctr_help(&rcu_bh_ctrlblk))
  98                 raise_softirq(RCU_SOFTIRQ);
  99         local_irq_restore(flags);
 100 }
 101
 102 /*
 103  * Record an rcu_bh quiescent state.
 104  */
 105 void rcu_bh_qs(void)
 106 {
 107         unsigned long flags;
 108
 109         local_irq_save(flags);
 110         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 111                 raise_softirq(RCU_SOFTIRQ);
 112         local_irq_restore(flags);
 113 }
 114
 115 /*
 116  * Check to see if the scheduling-clock interrupt came from an extended
 117  * quiescent state, and, if so, tell RCU about it.  This function must
 118  * be called from hardirq context.  It is normally called from the
 119  * scheduling-clock interrupt.
 120  */
 121 void rcu_check_callbacks(int user)
 122 {
 123         if (user)
 124                 rcu_sched_qs();
 125         if (user || !in_softirq())
 126                 rcu_bh_qs();
 127 }
 128
 129 /*
 130  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 131  * whose grace period has elapsed.
 132  */
 133 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 134 {
 135         struct rcu_head *next, *list;
 136         unsigned long flags;
 137
 138         /* Move the ready-to-invoke callbacks to a local list. */
 139         local_irq_save(flags);
 140         if (rcp->donetail == &rcp->rcucblist) {
 141                 /* No callbacks ready, so just leave. */
 142                 local_irq_restore(flags);
 143                 return;
 144         }
 145         list = rcp->rcucblist;
 146         rcp->rcucblist = *rcp->donetail;
 147         *rcp->donetail = NULL;
 148         if (rcp->curtail == rcp->donetail)
 149                 rcp->curtail = &rcp->rcucblist;
 150         rcp->donetail = &rcp->rcucblist;
 151         local_irq_restore(flags);
 152
 153         /* Invoke the callbacks on the local list. */
 154         while (list) {
 155                 next = list->next;
 156                 prefetch(next);
 157                 debug_rcu_head_unqueue(list);
 158                 local_bh_disable();
 159                 __rcu_reclaim("", list);
 160                 local_bh_enable();
 161                 list = next;
 162         }
 163 }
 164
 165 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
 166 {
 167         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 168         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 169 }
 170
 171 /*
 172  * Wait for a grace period to elapse.  But it is illegal to invoke
 173  * synchronize_sched() from within an RCU read-side critical section.
 174  * Therefore, any legal call to synchronize_sched() is a quiescent
 175  * state, and so on a UP system, synchronize_sched() need do nothing.
 176  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 177  * benefits of doing might_sleep() to reduce latency.)
 178  *
 179  * Cool, huh?  (Due to Josh Triplett.)
 180  */
 181 void synchronize_sched(void)
 182 {
 183         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
 184                          lock_is_held(&rcu_lock_map) ||
 185                          lock_is_held(&rcu_sched_lock_map),
 186                          "Illegal synchronize_sched() in RCU read-side critical section");
 187 }
 188 EXPORT_SYMBOL_GPL(synchronize_sched);
 189
 190 /*
 191  * Helper function for call_rcu() and call_rcu_bh().
 192  */
 193 static void __call_rcu(struct rcu_head *head,
 194                        rcu_callback_t func,
 195                        struct rcu_ctrlblk *rcp)
 196 {
 197         unsigned long flags;
 198
 199         debug_rcu_head_queue(head);
 200         head->func = func;
 201         head->next = NULL;
 202
 203         local_irq_save(flags);
 204         *rcp->curtail = head;
 205         rcp->curtail = &head->next;
 206         local_irq_restore(flags);
 207
 208         if (unlikely(is_idle_task(current))) {
 209                 /* force scheduling for rcu_sched_qs() */
 210                 resched_cpu(0);
 211         }
 212 }
 213
 214 /*
 215  * Post an RCU callback to be invoked after the end of an RCU-sched grace
 216  * period.  But since we have but one CPU, that would be after any
 217  * quiescent state.
 218  */
 219 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
 220 {
 221         __call_rcu(head, func, &rcu_sched_ctrlblk);
 222 }
 223 EXPORT_SYMBOL_GPL(call_rcu_sched);
 224
 225 /*
 226  * Post an RCU bottom-half callback to be invoked after any subsequent
 227  * quiescent state.
 228  */
 229 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
 230 {
 231         __call_rcu(head, func, &rcu_bh_ctrlblk);
 232 }
 233 EXPORT_SYMBOL_GPL(call_rcu_bh);
 234
 235 void __init rcu_init(void)
 236 {
 237         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 238         rcu_early_boot_tests();
 239 }