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 __call_rcu(struct rcu_head *head,
  45                        rcu_callback_t func,
  46                        struct rcu_ctrlblk *rcp);
  47
  48 #include "tiny_plugin.h"
  49
  50 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
  51
  52 /*
  53  * Test whether RCU thinks that the current CPU is idle.
  54  */
  55 bool notrace __rcu_is_watching(void)
  56 {
  57         return true;
  58 }
  59 EXPORT_SYMBOL(__rcu_is_watching);
  60
  61 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
  62
  63 /*
  64  * Helper function for rcu_sched_qs() and rcu_bh_qs().
  65  * Also irqs are disabled to avoid confusion due to interrupt handlers
  66  * invoking call_rcu().
  67  */
  68 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  69 {
  70         RCU_TRACE(reset_cpu_stall_ticks(rcp));
  71         if (rcp->donetail != rcp->curtail) {
  72                 rcp->donetail = rcp->curtail;
  73                 return 1;
  74         }
  75
  76         return 0;
  77 }
  78
  79 /*
  80  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
  81  * are at it, given that any rcu quiescent state is also an rcu_bh
  82  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
  83  */
  84 void rcu_sched_qs(void)
  85 {
  86         unsigned long flags;
  87
  88         local_irq_save(flags);
  89         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
  90             rcu_qsctr_help(&rcu_bh_ctrlblk))
  91                 raise_softirq(RCU_SOFTIRQ);
  92         local_irq_restore(flags);
  93 }
  94
  95 /*
  96  * Record an rcu_bh quiescent state.
  97  */
  98 void rcu_bh_qs(void)
  99 {
 100         unsigned long flags;
 101
 102         local_irq_save(flags);
 103         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 104                 raise_softirq(RCU_SOFTIRQ);
 105         local_irq_restore(flags);
 106 }
 107
 108 /*
 109  * Check to see if the scheduling-clock interrupt came from an extended
 110  * quiescent state, and, if so, tell RCU about it.  This function must
 111  * be called from hardirq context.  It is normally called from the
 112  * scheduling-clock interrupt.
 113  */
 114 void rcu_check_callbacks(int user)
 115 {
 116         RCU_TRACE(check_cpu_stalls());
 117         if (user)
 118                 rcu_sched_qs();
 119         else if (!in_softirq())
 120                 rcu_bh_qs();
 121         if (user)
 122                 rcu_note_voluntary_context_switch(current);
 123 }
 124
 125 /*
 126  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 127  * whose grace period has elapsed.
 128  */
 129 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 130 {
 131         const char *rn = NULL;
 132         struct rcu_head *next, *list;
 133         unsigned long flags;
 134         RCU_TRACE(int cb_count = 0);
 135
 136         /* Move the ready-to-invoke callbacks to a local list. */
 137         local_irq_save(flags);
 138         if (rcp->donetail == &rcp->rcucblist) {
 139                 /* No callbacks ready, so just leave. */
 140                 local_irq_restore(flags);
 141                 return;
 142         }
 143         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 144         list = rcp->rcucblist;
 145         rcp->rcucblist = *rcp->donetail;
 146         *rcp->donetail = NULL;
 147         if (rcp->curtail == rcp->donetail)
 148                 rcp->curtail = &rcp->rcucblist;
 149         rcp->donetail = &rcp->rcucblist;
 150         local_irq_restore(flags);
 151
 152         /* Invoke the callbacks on the local list. */
 153         RCU_TRACE(rn = rcp->name);
 154         while (list) {
 155                 next = list->next;
 156                 prefetch(next);
 157                 debug_rcu_head_unqueue(list);
 158                 local_bh_disable();
 159                 __rcu_reclaim(rn, list);
 160                 local_bh_enable();
 161                 list = next;
 162                 RCU_TRACE(cb_count++);
 163         }
 164         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 165         RCU_TRACE(trace_rcu_batch_end(rcp->name,
 166                                       cb_count, 0, need_resched(),
 167                                       is_idle_task(current),
 168                                       false));
 169 }
 170
 171 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
 172 {
 173         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 174         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 175 }
 176
 177 /*
 178  * Wait for a grace period to elapse.  But it is illegal to invoke
 179  * synchronize_sched() from within an RCU read-side critical section.
 180  * Therefore, any legal call to synchronize_sched() is a quiescent
 181  * state, and so on a UP system, synchronize_sched() need do nothing.
 182  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 183  * benefits of doing might_sleep() to reduce latency.)
 184  *
 185  * Cool, huh?  (Due to Josh Triplett.)
 186  */
 187 void synchronize_sched(void)
 188 {
 189         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
 190                          lock_is_held(&rcu_lock_map) ||
 191                          lock_is_held(&rcu_sched_lock_map),
 192                          "Illegal synchronize_sched() in RCU read-side critical section");
 193 }
 194 EXPORT_SYMBOL_GPL(synchronize_sched);
 195
 196 /*
 197  * Helper function for call_rcu() and call_rcu_bh().
 198  */
 199 static void __call_rcu(struct rcu_head *head,
 200                        rcu_callback_t func,
 201                        struct rcu_ctrlblk *rcp)
 202 {
 203         unsigned long flags;
 204
 205         debug_rcu_head_queue(head);
 206         head->func = func;
 207         head->next = NULL;
 208
 209         local_irq_save(flags);
 210         *rcp->curtail = head;
 211         rcp->curtail = &head->next;
 212         RCU_TRACE(rcp->qlen++);
 213         local_irq_restore(flags);
 214
 215         if (unlikely(is_idle_task(current))) {
 216                 /* force scheduling for rcu_sched_qs() */
 217                 resched_cpu(0);
 218         }
 219 }
 220
 221 /*
 222  * Post an RCU callback to be invoked after the end of an RCU-sched grace
 223  * period.  But since we have but one CPU, that would be after any
 224  * quiescent state.
 225  */
 226 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
 227 {
 228         __call_rcu(head, func, &rcu_sched_ctrlblk);
 229 }
 230 EXPORT_SYMBOL_GPL(call_rcu_sched);
 231
 232 /*
 233  * Post an RCU bottom-half callback to be invoked after any subsequent
 234  * quiescent state.
 235  */
 236 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
 237 {
 238         __call_rcu(head, func, &rcu_bh_ctrlblk);
 239 }
 240 EXPORT_SYMBOL_GPL(call_rcu_bh);
 241
 242 void __init rcu_init(void)
 243 {
 244         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 245         RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
 246         RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
 247
 248         rcu_early_boot_tests();
 249 }