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.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 #include <linux/trace_events.h>
  39
  40 #include "rcu.h"
  41
  42 /* Forward declarations for tiny_plugin.h. */
  43 struct rcu_ctrlblk;
  44 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
  45 static void rcu_process_callbacks(struct softirq_action *unused);
  46 static void __call_rcu(struct rcu_head *head,
  47                        rcu_callback_t func,
  48                        struct rcu_ctrlblk *rcp);
  49
  50 #include "tiny_plugin.h"
  51
  52 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
  53
  54 /*
  55  * Test whether RCU thinks that the current CPU is idle.
  56  */
  57 bool notrace __rcu_is_watching(void)
  58 {
  59         return true;
  60 }
  61 EXPORT_SYMBOL(__rcu_is_watching);
  62
  63 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
  64
  65 /*
  66  * Helper function for rcu_sched_qs() and rcu_bh_qs().
  67  * Also irqs are disabled to avoid confusion due to interrupt handlers
  68  * invoking call_rcu().
  69  */
  70 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  71 {
  72         RCU_TRACE(reset_cpu_stall_ticks(rcp));
  73         if (rcp->donetail != rcp->curtail) {
  74                 rcp->donetail = rcp->curtail;
  75                 return 1;
  76         }
  77
  78         return 0;
  79 }
  80
  81 /*
  82  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
  83  * are at it, given that any rcu quiescent state is also an rcu_bh
  84  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
  85  */
  86 void rcu_sched_qs(void)
  87 {
  88         unsigned long flags;
  89
  90         local_irq_save(flags);
  91         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
  92             rcu_qsctr_help(&rcu_bh_ctrlblk))
  93                 raise_softirq(RCU_SOFTIRQ);
  94         local_irq_restore(flags);
  95 }
  96
  97 /*
  98  * Record an rcu_bh quiescent state.
  99  */
 100 void rcu_bh_qs(void)
 101 {
 102         unsigned long flags;
 103
 104         local_irq_save(flags);
 105         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 106                 raise_softirq(RCU_SOFTIRQ);
 107         local_irq_restore(flags);
 108 }
 109
 110 /*
 111  * Check to see if the scheduling-clock interrupt came from an extended
 112  * quiescent state, and, if so, tell RCU about it.  This function must
 113  * be called from hardirq context.  It is normally called from the
 114  * scheduling-clock interrupt.
 115  */
 116 void rcu_check_callbacks(int user)
 117 {
 118         RCU_TRACE(check_cpu_stalls());
 119         if (user)
 120                 rcu_sched_qs();
 121         else if (!in_softirq())
 122                 rcu_bh_qs();
 123         if (user)
 124                 rcu_note_voluntary_context_switch(current);
 125 }
 126
 127 /*
 128  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 129  * whose grace period has elapsed.
 130  */
 131 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 132 {
 133         const char *rn = NULL;
 134         struct rcu_head *next, *list;
 135         unsigned long flags;
 136         RCU_TRACE(int cb_count = 0);
 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         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 146         list = rcp->rcucblist;
 147         rcp->rcucblist = *rcp->donetail;
 148         *rcp->donetail = NULL;
 149         if (rcp->curtail == rcp->donetail)
 150                 rcp->curtail = &rcp->rcucblist;
 151         rcp->donetail = &rcp->rcucblist;
 152         local_irq_restore(flags);
 153
 154         /* Invoke the callbacks on the local list. */
 155         RCU_TRACE(rn = rcp->name);
 156         while (list) {
 157                 next = list->next;
 158                 prefetch(next);
 159                 debug_rcu_head_unqueue(list);
 160                 local_bh_disable();
 161                 __rcu_reclaim(rn, list);
 162                 local_bh_enable();
 163                 list = next;
 164                 RCU_TRACE(cb_count++);
 165         }
 166         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 167         RCU_TRACE(trace_rcu_batch_end(rcp->name,
 168                                       cb_count, 0, need_resched(),
 169                                       is_idle_task(current),
 170                                       false));
 171 }
 172
 173 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
 174 {
 175         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 176         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 177 }
 178
 179 /*
 180  * Wait for a grace period to elapse.  But it is illegal to invoke
 181  * synchronize_sched() from within an RCU read-side critical section.
 182  * Therefore, any legal call to synchronize_sched() is a quiescent
 183  * state, and so on a UP system, synchronize_sched() need do nothing.
 184  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 185  * benefits of doing might_sleep() to reduce latency.)
 186  *
 187  * Cool, huh?  (Due to Josh Triplett.)
 188  *
 189  * But we want to make this a static inline later.  The cond_resched()
 190  * currently makes this problematic.
 191  */
 192 void synchronize_sched(void)
 193 {
 194         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
 195                          lock_is_held(&rcu_lock_map) ||
 196                          lock_is_held(&rcu_sched_lock_map),
 197                          "Illegal synchronize_sched() in RCU read-side critical section");
 198         cond_resched();
 199 }
 200 EXPORT_SYMBOL_GPL(synchronize_sched);
 201
 202 /*
 203  * Helper function for call_rcu() and call_rcu_bh().
 204  */
 205 static void __call_rcu(struct rcu_head *head,
 206                        rcu_callback_t func,
 207                        struct rcu_ctrlblk *rcp)
 208 {
 209         unsigned long flags;
 210
 211         debug_rcu_head_queue(head);
 212         head->func = func;
 213         head->next = NULL;
 214
 215         local_irq_save(flags);
 216         *rcp->curtail = head;
 217         rcp->curtail = &head->next;
 218         RCU_TRACE(rcp->qlen++);
 219         local_irq_restore(flags);
 220
 221         if (unlikely(is_idle_task(current))) {
 222                 /* force scheduling for rcu_sched_qs() */
 223                 resched_cpu(0);
 224         }
 225 }
 226
 227 /*
 228  * Post an RCU callback to be invoked after the end of an RCU-sched grace
 229  * period.  But since we have but one CPU, that would be after any
 230  * quiescent state.
 231  */
 232 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
 233 {
 234         __call_rcu(head, func, &rcu_sched_ctrlblk);
 235 }
 236 EXPORT_SYMBOL_GPL(call_rcu_sched);
 237
 238 /*
 239  * Post an RCU bottom-half callback to be invoked after any subsequent
 240  * quiescent state.
 241  */
 242 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
 243 {
 244         __call_rcu(head, func, &rcu_bh_ctrlblk);
 245 }
 246 EXPORT_SYMBOL_GPL(call_rcu_bh);
 247
 248 void __init rcu_init(void)
 249 {
 250         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 251         RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
 252         RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
 253
 254         rcu_early_boot_tests();
 255 }