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->donetail != rcp->curtail) {
 107                 rcp->donetail = rcp->curtail;
 108                 return 1;
 109         }
 110
 111         return 0;
 112 }
 113
 114 /*
 115  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 116  * are at it, given that any rcu quiescent state is also an rcu_bh
 117  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 118  */
 119 void rcu_sched_qs(void)
 120 {
 121         unsigned long flags;
 122
 123         local_irq_save(flags);
 124         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 125             rcu_qsctr_help(&rcu_bh_ctrlblk))
 126                 raise_softirq(RCU_SOFTIRQ);
 127         local_irq_restore(flags);
 128 }
 129
 130 /*
 131  * Record an rcu_bh quiescent state.
 132  */
 133 void rcu_bh_qs(void)
 134 {
 135         unsigned long flags;
 136
 137         local_irq_save(flags);
 138         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 139                 raise_softirq(RCU_SOFTIRQ);
 140         local_irq_restore(flags);
 141 }
 142
 143 /*
 144  * Check to see if the scheduling-clock interrupt came from an extended
 145  * quiescent state, and, if so, tell RCU about it.  This function must
 146  * be called from hardirq context.  It is normally called from the
 147  * scheduling-clock interrupt.
 148  */
 149 void rcu_check_callbacks(int user)
 150 {
 151         RCU_TRACE(check_cpu_stalls());
 152         if (user)
 153                 rcu_sched_qs();
 154         else if (!in_softirq())
 155                 rcu_bh_qs();
 156         if (user)
 157                 rcu_note_voluntary_context_switch(current);
 158 }
 159
 160 /*
 161  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 162  * whose grace period has elapsed.
 163  */
 164 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 165 {
 166         const char *rn = NULL;
 167         struct rcu_head *next, *list;
 168         unsigned long flags;
 169         RCU_TRACE(int cb_count = 0);
 170
 171         /* Move the ready-to-invoke callbacks to a local list. */
 172         local_irq_save(flags);
 173         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 174         list = rcp->rcucblist;
 175         rcp->rcucblist = *rcp->donetail;
 176         *rcp->donetail = NULL;
 177         if (rcp->curtail == rcp->donetail)
 178                 rcp->curtail = &rcp->rcucblist;
 179         rcp->donetail = &rcp->rcucblist;
 180         local_irq_restore(flags);
 181
 182         /* Invoke the callbacks on the local list. */
 183         RCU_TRACE(rn = rcp->name);
 184         while (list) {
 185                 next = list->next;
 186                 prefetch(next);
 187                 debug_rcu_head_unqueue(list);
 188                 local_bh_disable();
 189                 __rcu_reclaim(rn, list);
 190                 local_bh_enable();
 191                 list = next;
 192                 RCU_TRACE(cb_count++);
 193         }
 194         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 195         RCU_TRACE(trace_rcu_batch_end(rcp->name,
 196                                       cb_count, 0, need_resched(),
 197                                       is_idle_task(current),
 198                                       false));
 199 }
 200
 201 static void rcu_process_callbacks(struct softirq_action *unused)
 202 {
 203         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 204         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 205 }
 206
 207 /*
 208  * Wait for a grace period to elapse.  But it is illegal to invoke
 209  * synchronize_sched() from within an RCU read-side critical section.
 210  * Therefore, any legal call to synchronize_sched() is a quiescent
 211  * state, and so on a UP system, synchronize_sched() need do nothing.
 212  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 213  * benefits of doing might_sleep() to reduce latency.)
 214  *
 215  * Cool, huh?  (Due to Josh Triplett.)
 216  *
 217  * But we want to make this a static inline later.  The cond_resched()
 218  * currently makes this problematic.
 219  */
 220 void synchronize_sched(void)
 221 {
 222         rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 223                            !lock_is_held(&rcu_lock_map) &&
 224                            !lock_is_held(&rcu_sched_lock_map),
 225                            "Illegal synchronize_sched() in RCU read-side critical section");
 226         cond_resched();
 227 }
 228 EXPORT_SYMBOL_GPL(synchronize_sched);
 229
 230 /*
 231  * Helper function for call_rcu() and call_rcu_bh().
 232  */
 233 static void __call_rcu(struct rcu_head *head,
 234                        void (*func)(struct rcu_head *rcu),
 235                        struct rcu_ctrlblk *rcp)
 236 {
 237         unsigned long flags;
 238
 239         debug_rcu_head_queue(head);
 240         head->func = func;
 241         head->next = NULL;
 242
 243         local_irq_save(flags);
 244         *rcp->curtail = head;
 245         rcp->curtail = &head->next;
 246         RCU_TRACE(rcp->qlen++);
 247         local_irq_restore(flags);
 248
 249         if (unlikely(is_idle_task(current))) {
 250                 /* force scheduling for rcu_sched_qs() */
 251                 resched_cpu(0);
 252         }
 253 }
 254
 255 /*
 256  * Post an RCU callback to be invoked after the end of an RCU-sched grace
 257  * period.  But since we have but one CPU, that would be after any
 258  * quiescent state.
 259  */
 260 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 261 {
 262         __call_rcu(head, func, &rcu_sched_ctrlblk);
 263 }
 264 EXPORT_SYMBOL_GPL(call_rcu_sched);
 265
 266 /*
 267  * Post an RCU bottom-half callback to be invoked after any subsequent
 268  * quiescent state.
 269  */
 270 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 271 {
 272         __call_rcu(head, func, &rcu_bh_ctrlblk);
 273 }
 274 EXPORT_SYMBOL_GPL(call_rcu_bh);
 275
 276 void __init rcu_init(void)
 277 {
 278         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 279         RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
 280         RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
 281
 282         rcu_early_boot_tests();
 283 }