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/ftrace_event.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                        void (*func)(struct rcu_head *rcu),
  48                        struct rcu_ctrlblk *rcp);
  49
  50 #include "tiny_plugin.h"
  51
  52 /*
  53  * Enter idle, which is an extended quiescent state if we have fully
  54  * entered that mode.
  55  */
  56 void rcu_idle_enter(void)
  57 {
  58 }
  59 EXPORT_SYMBOL_GPL(rcu_idle_enter);
  60
  61 /*
  62  * Exit an interrupt handler towards idle.
  63  */
  64 void rcu_irq_exit(void)
  65 {
  66 }
  67 EXPORT_SYMBOL_GPL(rcu_irq_exit);
  68
  69 /*
  70  * Exit idle, so that we are no longer in an extended quiescent state.
  71  */
  72 void rcu_idle_exit(void)
  73 {
  74 }
  75 EXPORT_SYMBOL_GPL(rcu_idle_exit);
  76
  77 /*
  78  * Enter an interrupt handler, moving away from idle.
  79  */
  80 void rcu_irq_enter(void)
  81 {
  82 }
  83 EXPORT_SYMBOL_GPL(rcu_irq_enter);
  84
  85 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
  86
  87 /*
  88  * Test whether RCU thinks that the current CPU is idle.
  89  */
  90 bool notrace __rcu_is_watching(void)
  91 {
  92         return true;
  93 }
  94 EXPORT_SYMBOL(__rcu_is_watching);
  95
  96 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
  97
  98 /*
  99  * Helper function for rcu_sched_qs() and rcu_bh_qs().
 100  * Also irqs are disabled to avoid confusion due to interrupt handlers
 101  * invoking call_rcu().
 102  */
 103 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 104 {
 105         RCU_TRACE(reset_cpu_stall_ticks(rcp));
 106         if (rcp->rcucblist != NULL &&
 107             rcp->donetail != rcp->curtail) {
 108                 rcp->donetail = rcp->curtail;
 109                 return 1;
 110         }
 111
 112         return 0;
 113 }
 114
 115 /*
 116  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 117  * are at it, given that any rcu quiescent state is also an rcu_bh
 118  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 119  */
 120 void rcu_sched_qs(void)
 121 {
 122         unsigned long flags;
 123
 124         local_irq_save(flags);
 125         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 126             rcu_qsctr_help(&rcu_bh_ctrlblk))
 127                 raise_softirq(RCU_SOFTIRQ);
 128         local_irq_restore(flags);
 129 }
 130
 131 /*
 132  * Record an rcu_bh quiescent state.
 133  */
 134 void rcu_bh_qs(void)
 135 {
 136         unsigned long flags;
 137
 138         local_irq_save(flags);
 139         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 140                 raise_softirq(RCU_SOFTIRQ);
 141         local_irq_restore(flags);
 142 }
 143
 144 /*
 145  * Check to see if the scheduling-clock interrupt came from an extended
 146  * quiescent state, and, if so, tell RCU about it.  This function must
 147  * be called from hardirq context.  It is normally called from the
 148  * scheduling-clock interrupt.
 149  */
 150 void rcu_check_callbacks(int user)
 151 {
 152         RCU_TRACE(check_cpu_stalls());
 153         if (user)
 154                 rcu_sched_qs();
 155         else if (!in_softirq())
 156                 rcu_bh_qs();
 157         if (user)
 158                 rcu_note_voluntary_context_switch(current);
 159 }
 160
 161 /*
 162  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 163  * whose grace period has elapsed.
 164  */
 165 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 166 {
 167         const char *rn = NULL;
 168         struct rcu_head *next, *list;
 169         unsigned long flags;
 170         RCU_TRACE(int cb_count = 0);
 171
 172         /* If no RCU callbacks ready to invoke, just return. */
 173         if (&rcp->rcucblist == rcp->donetail) {
 174                 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
 175                 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
 176                                               !!ACCESS_ONCE(rcp->rcucblist),
 177                                               need_resched(),
 178                                               is_idle_task(current),
 179                                               false));
 180                 return;
 181         }
 182
 183         /* Move the ready-to-invoke callbacks to a local list. */
 184         local_irq_save(flags);
 185         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 186         list = rcp->rcucblist;
 187         rcp->rcucblist = *rcp->donetail;
 188         *rcp->donetail = NULL;
 189         if (rcp->curtail == rcp->donetail)
 190                 rcp->curtail = &rcp->rcucblist;
 191         rcp->donetail = &rcp->rcucblist;
 192         local_irq_restore(flags);
 193
 194         /* Invoke the callbacks on the local list. */
 195         RCU_TRACE(rn = rcp->name);
 196         while (list) {
 197                 next = list->next;
 198                 prefetch(next);
 199                 debug_rcu_head_unqueue(list);
 200                 local_bh_disable();
 201                 __rcu_reclaim(rn, list);
 202                 local_bh_enable();
 203                 list = next;
 204                 RCU_TRACE(cb_count++);
 205         }
 206         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 207         RCU_TRACE(trace_rcu_batch_end(rcp->name,
 208                                       cb_count, 0, need_resched(),
 209                                       is_idle_task(current),
 210                                       false));
 211 }
 212
 213 static void rcu_process_callbacks(struct softirq_action *unused)
 214 {
 215         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 216         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 217 }
 218
 219 /*
 220  * Wait for a grace period to elapse.  But it is illegal to invoke
 221  * synchronize_sched() from within an RCU read-side critical section.
 222  * Therefore, any legal call to synchronize_sched() is a quiescent
 223  * state, and so on a UP system, synchronize_sched() need do nothing.
 224  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 225  * benefits of doing might_sleep() to reduce latency.)
 226  *
 227  * Cool, huh?  (Due to Josh Triplett.)
 228  *
 229  * But we want to make this a static inline later.  The cond_resched()
 230  * currently makes this problematic.
 231  */
 232 void synchronize_sched(void)
 233 {
 234         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 235                            !lock_is_held(&rcu_lock_map) &&
 236                            !lock_is_held(&rcu_sched_lock_map),
 237                            "Illegal synchronize_sched() in RCU read-side critical section");
 238         cond_resched();
 239 }
 240 EXPORT_SYMBOL_GPL(synchronize_sched);
 241
 242 /*
 243  * Helper function for call_rcu() and call_rcu_bh().
 244  */
 245 static void __call_rcu(struct rcu_head *head,
 246                        void (*func)(struct rcu_head *rcu),
 247                        struct rcu_ctrlblk *rcp)
 248 {
 249         unsigned long flags;
 250
 251         debug_rcu_head_queue(head);
 252         head->func = func;
 253         head->next = NULL;
 254
 255         local_irq_save(flags);
 256         *rcp->curtail = head;
 257         rcp->curtail = &head->next;
 258         RCU_TRACE(rcp->qlen++);
 259         local_irq_restore(flags);
 260
 261         if (unlikely(is_idle_task(current))) {
 262                 /* force scheduling for rcu_sched_qs() */
 263                 resched_cpu(0);
 264         }
 265 }
 266
 267 /*
 268  * Post an RCU callback to be invoked after the end of an RCU-sched grace
 269  * period.  But since we have but one CPU, that would be after any
 270  * quiescent state.
 271  */
 272 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 273 {
 274         __call_rcu(head, func, &rcu_sched_ctrlblk);
 275 }
 276 EXPORT_SYMBOL_GPL(call_rcu_sched);
 277
 278 /*
 279  * Post an RCU bottom-half callback to be invoked after any subsequent
 280  * quiescent state.
 281  */
 282 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 283 {
 284         __call_rcu(head, func, &rcu_bh_ctrlblk);
 285 }
 286 EXPORT_SYMBOL_GPL(call_rcu_bh);
 287
 288 void __init rcu_init(void)
 289 {
 290         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 291         RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
 292         RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
 293
 294         rcu_early_boot_tests();
 295 }