kernel/rcutiny.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, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  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
  39 #ifdef CONFIG_RCU_TRACE
  40 #include <trace/events/rcu.h>
  41 #endif /* #else #ifdef CONFIG_RCU_TRACE */
  42
  43 #include "rcu.h"
  44
  45 /* Forward declarations for rcutiny_plugin.h. */
  46 struct rcu_ctrlblk;
  47 static void invoke_rcu_callbacks(void);
  48 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
  49 static void rcu_process_callbacks(struct softirq_action *unused);
  50 static void __call_rcu(struct rcu_head *head,
  51                        void (*func)(struct rcu_head *rcu),
  52                        struct rcu_ctrlblk *rcp);
  53
  54 #include "rcutiny_plugin.h"
  55
  56 #ifdef CONFIG_NO_HZ
  57
  58 static long rcu_dynticks_nesting = 1;
  59
  60 /*
  61  * Enter dynticks-idle mode, which is an extended quiescent state
  62  * if we have fully entered that mode (i.e., if the new value of
  63  * dynticks_nesting is zero).
  64  */
  65 void rcu_enter_nohz(void)
  66 {
  67         if (--rcu_dynticks_nesting == 0)
  68                 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
  69 }
  70
  71 /*
  72  * Exit dynticks-idle mode, so that we are no longer in an extended
  73  * quiescent state.
  74  */
  75 void rcu_exit_nohz(void)
  76 {
  77         rcu_dynticks_nesting++;
  78 }
  79
  80 #endif /* #ifdef CONFIG_NO_HZ */
  81
  82 /*
  83  * Helper function for rcu_sched_qs() and rcu_bh_qs().
  84  * Also irqs are disabled to avoid confusion due to interrupt handlers
  85  * invoking call_rcu().
  86  */
  87 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  88 {
  89         if (rcp->rcucblist != NULL &&
  90             rcp->donetail != rcp->curtail) {
  91                 rcp->donetail = rcp->curtail;
  92                 return 1;
  93         }
  94
  95         return 0;
  96 }
  97
  98 /*
  99  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 100  * are at it, given that any rcu quiescent state is also an rcu_bh
 101  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 102  */
 103 void rcu_sched_qs(int cpu)
 104 {
 105         unsigned long flags;
 106
 107         local_irq_save(flags);
 108         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 109             rcu_qsctr_help(&rcu_bh_ctrlblk))
 110                 invoke_rcu_callbacks();
 111         local_irq_restore(flags);
 112 }
 113
 114 /*
 115  * Record an rcu_bh quiescent state.
 116  */
 117 void rcu_bh_qs(int cpu)
 118 {
 119         unsigned long flags;
 120
 121         local_irq_save(flags);
 122         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 123                 invoke_rcu_callbacks();
 124         local_irq_restore(flags);
 125 }
 126
 127 /*
 128  * Check to see if the scheduling-clock interrupt came from an extended
 129  * quiescent state, and, if so, tell RCU about it.
 130  */
 131 void rcu_check_callbacks(int cpu, int user)
 132 {
 133         if (user ||
 134             (idle_cpu(cpu) &&
 135              !in_softirq() &&
 136              hardirq_count() <= (1 << HARDIRQ_SHIFT)))
 137                 rcu_sched_qs(cpu);
 138         else if (!in_softirq())
 139                 rcu_bh_qs(cpu);
 140         rcu_preempt_check_callbacks();
 141 }
 142
 143 /*
 144  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 145  * whose grace period has elapsed.
 146  */
 147 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 148 {
 149         char *rn = NULL;
 150         struct rcu_head *next, *list;
 151         unsigned long flags;
 152         RCU_TRACE(int cb_count = 0);
 153
 154         /* If no RCU callbacks ready to invoke, just return. */
 155         if (&rcp->rcucblist == rcp->donetail) {
 156                 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
 157                 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0));
 158                 return;
 159         }
 160
 161         /* Move the ready-to-invoke callbacks to a local list. */
 162         local_irq_save(flags);
 163         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
 164         list = rcp->rcucblist;
 165         rcp->rcucblist = *rcp->donetail;
 166         *rcp->donetail = NULL;
 167         if (rcp->curtail == rcp->donetail)
 168                 rcp->curtail = &rcp->rcucblist;
 169         rcu_preempt_remove_callbacks(rcp);
 170         rcp->donetail = &rcp->rcucblist;
 171         local_irq_restore(flags);
 172
 173         /* Invoke the callbacks on the local list. */
 174         RCU_TRACE(rn = rcp->name);
 175         while (list) {
 176                 next = list->next;
 177                 prefetch(next);
 178                 debug_rcu_head_unqueue(list);
 179                 local_bh_disable();
 180                 __rcu_reclaim(rn, list);
 181                 local_bh_enable();
 182                 list = next;
 183                 RCU_TRACE(cb_count++);
 184         }
 185         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 186         RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count));
 187 }
 188
 189 static void rcu_process_callbacks(struct softirq_action *unused)
 190 {
 191         __rcu_process_callbacks(&rcu_sched_ctrlblk);
 192         __rcu_process_callbacks(&rcu_bh_ctrlblk);
 193         rcu_preempt_process_callbacks();
 194 }
 195
 196 /*
 197  * Wait for a grace period to elapse.  But it is illegal to invoke
 198  * synchronize_sched() from within an RCU read-side critical section.
 199  * Therefore, any legal call to synchronize_sched() is a quiescent
 200  * state, and so on a UP system, synchronize_sched() need do nothing.
 201  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 202  * benefits of doing might_sleep() to reduce latency.)
 203  *
 204  * Cool, huh?  (Due to Josh Triplett.)
 205  *
 206  * But we want to make this a static inline later.  The cond_resched()
 207  * currently makes this problematic.
 208  */
 209 void synchronize_sched(void)
 210 {
 211         cond_resched();
 212 }
 213 EXPORT_SYMBOL_GPL(synchronize_sched);
 214
 215 /*
 216  * Helper function for call_rcu() and call_rcu_bh().
 217  */
 218 static void __call_rcu(struct rcu_head *head,
 219                        void (*func)(struct rcu_head *rcu),
 220                        struct rcu_ctrlblk *rcp)
 221 {
 222         unsigned long flags;
 223
 224         debug_rcu_head_queue(head);
 225         head->func = func;
 226         head->next = NULL;
 227
 228         local_irq_save(flags);
 229         *rcp->curtail = head;
 230         rcp->curtail = &head->next;
 231         RCU_TRACE(rcp->qlen++);
 232         local_irq_restore(flags);
 233 }
 234
 235 /*
 236  * Post an RCU callback to be invoked after the end of an RCU-sched grace
 237  * period.  But since we have but one CPU, that would be after any
 238  * quiescent state.
 239  */
 240 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 241 {
 242         __call_rcu(head, func, &rcu_sched_ctrlblk);
 243 }
 244 EXPORT_SYMBOL_GPL(call_rcu_sched);
 245
 246 /*
 247  * Post an RCU bottom-half callback to be invoked after any subsequent
 248  * quiescent state.
 249  */
 250 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 251 {
 252         __call_rcu(head, func, &rcu_bh_ctrlblk);
 253 }
 254 EXPORT_SYMBOL_GPL(call_rcu_bh);