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