linux/kernel/rcutiny.c
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   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. */
  46struct rcu_ctrlblk;
  47static void invoke_rcu_callbacks(void);
  48static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
  49static void rcu_process_callbacks(struct softirq_action *unused);
  50static 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
  56static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
  57
  58/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
  59static void rcu_idle_enter_common(long long oldval)
  60{
  61        if (rcu_dynticks_nesting) {
  62                RCU_TRACE(trace_rcu_dyntick("--=",
  63                                            oldval, rcu_dynticks_nesting));
  64                return;
  65        }
  66        RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
  67        if (!is_idle_task(current)) {
  68                struct task_struct *idle = idle_task(smp_processor_id());
  69
  70                RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
  71                                            oldval, rcu_dynticks_nesting));
  72                ftrace_dump(DUMP_ALL);
  73                WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
  74                          current->pid, current->comm,
  75                          idle->pid, idle->comm); /* must be idle task! */
  76        }
  77        rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
  78}
  79
  80/*
  81 * Enter idle, which is an extended quiescent state if we have fully
  82 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
  83 */
  84void rcu_idle_enter(void)
  85{
  86        unsigned long flags;
  87        long long oldval;
  88
  89        local_irq_save(flags);
  90        oldval = rcu_dynticks_nesting;
  91        rcu_dynticks_nesting = 0;
  92        rcu_idle_enter_common(oldval);
  93        local_irq_restore(flags);
  94}
  95
  96/*
  97 * Exit an interrupt handler towards idle.
  98 */
  99void rcu_irq_exit(void)
 100{
 101        unsigned long flags;
 102        long long oldval;
 103
 104        local_irq_save(flags);
 105        oldval = rcu_dynticks_nesting;
 106        rcu_dynticks_nesting--;
 107        WARN_ON_ONCE(rcu_dynticks_nesting < 0);
 108        rcu_idle_enter_common(oldval);
 109        local_irq_restore(flags);
 110}
 111
 112/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
 113static void rcu_idle_exit_common(long long oldval)
 114{
 115        if (oldval) {
 116                RCU_TRACE(trace_rcu_dyntick("++=",
 117                                            oldval, rcu_dynticks_nesting));
 118                return;
 119        }
 120        RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
 121        if (!is_idle_task(current)) {
 122                struct task_struct *idle = idle_task(smp_processor_id());
 123
 124                RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
 125                          oldval, rcu_dynticks_nesting));
 126                ftrace_dump(DUMP_ALL);
 127                WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
 128                          current->pid, current->comm,
 129                          idle->pid, idle->comm); /* must be idle task! */
 130        }
 131}
 132
 133/*
 134 * Exit idle, so that we are no longer in an extended quiescent state.
 135 */
 136void rcu_idle_exit(void)
 137{
 138        unsigned long flags;
 139        long long oldval;
 140
 141        local_irq_save(flags);
 142        oldval = rcu_dynticks_nesting;
 143        WARN_ON_ONCE(oldval != 0);
 144        rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
 145        rcu_idle_exit_common(oldval);
 146        local_irq_restore(flags);
 147}
 148
 149/*
 150 * Enter an interrupt handler, moving away from idle.
 151 */
 152void rcu_irq_enter(void)
 153{
 154        unsigned long flags;
 155        long long oldval;
 156
 157        local_irq_save(flags);
 158        oldval = rcu_dynticks_nesting;
 159        rcu_dynticks_nesting++;
 160        WARN_ON_ONCE(rcu_dynticks_nesting == 0);
 161        rcu_idle_exit_common(oldval);
 162        local_irq_restore(flags);
 163}
 164
 165#ifdef CONFIG_PROVE_RCU
 166
 167/*
 168 * Test whether RCU thinks that the current CPU is idle.
 169 */
 170int rcu_is_cpu_idle(void)
 171{
 172        return !rcu_dynticks_nesting;
 173}
 174EXPORT_SYMBOL(rcu_is_cpu_idle);
 175
 176#endif /* #ifdef CONFIG_PROVE_RCU */
 177
 178/*
 179 * Test whether the current CPU was interrupted from idle.  Nested
 180 * interrupts don't count, we must be running at the first interrupt
 181 * level.
 182 */
 183int rcu_is_cpu_rrupt_from_idle(void)
 184{
 185        return rcu_dynticks_nesting <= 0;
 186}
 187
 188/*
 189 * Helper function for rcu_sched_qs() and rcu_bh_qs().
 190 * Also irqs are disabled to avoid confusion due to interrupt handlers
 191 * invoking call_rcu().
 192 */
 193static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 194{
 195        if (rcp->rcucblist != NULL &&
 196            rcp->donetail != rcp->curtail) {
 197                rcp->donetail = rcp->curtail;
 198                return 1;
 199        }
 200
 201        return 0;
 202}
 203
 204/*
 205 * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 206 * are at it, given that any rcu quiescent state is also an rcu_bh
 207 * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 208 */
 209void rcu_sched_qs(int cpu)
 210{
 211        unsigned long flags;
 212
 213        local_irq_save(flags);
 214        if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 215            rcu_qsctr_help(&rcu_bh_ctrlblk))
 216                invoke_rcu_callbacks();
 217        local_irq_restore(flags);
 218}
 219
 220/*
 221 * Record an rcu_bh quiescent state.
 222 */
 223void rcu_bh_qs(int cpu)
 224{
 225        unsigned long flags;
 226
 227        local_irq_save(flags);
 228        if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 229                invoke_rcu_callbacks();
 230        local_irq_restore(flags);
 231}
 232
 233/*
 234 * Check to see if the scheduling-clock interrupt came from an extended
 235 * quiescent state, and, if so, tell RCU about it.  This function must
 236 * be called from hardirq context.  It is normally called from the
 237 * scheduling-clock interrupt.
 238 */
 239void rcu_check_callbacks(int cpu, int user)
 240{
 241        if (user || rcu_is_cpu_rrupt_from_idle())
 242                rcu_sched_qs(cpu);
 243        else if (!in_softirq())
 244                rcu_bh_qs(cpu);
 245        rcu_preempt_check_callbacks();
 246}
 247
 248/*
 249 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 250 * whose grace period has elapsed.
 251 */
 252static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 253{
 254        char *rn = NULL;
 255        struct rcu_head *next, *list;
 256        unsigned long flags;
 257        RCU_TRACE(int cb_count = 0);
 258
 259        /* If no RCU callbacks ready to invoke, just return. */
 260        if (&rcp->rcucblist == rcp->donetail) {
 261                RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
 262                RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
 263                                              ACCESS_ONCE(rcp->rcucblist),
 264                                              need_resched(),
 265                                              is_idle_task(current),
 266                                              rcu_is_callbacks_kthread()));
 267                return;
 268        }
 269
 270        /* Move the ready-to-invoke callbacks to a local list. */
 271        local_irq_save(flags);
 272        RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
 273        list = rcp->rcucblist;
 274        rcp->rcucblist = *rcp->donetail;
 275        *rcp->donetail = NULL;
 276        if (rcp->curtail == rcp->donetail)
 277                rcp->curtail = &rcp->rcucblist;
 278        rcu_preempt_remove_callbacks(rcp);
 279        rcp->donetail = &rcp->rcucblist;
 280        local_irq_restore(flags);
 281
 282        /* Invoke the callbacks on the local list. */
 283        RCU_TRACE(rn = rcp->name);
 284        while (list) {
 285                next = list->next;
 286                prefetch(next);
 287                debug_rcu_head_unqueue(list);
 288                local_bh_disable();
 289                __rcu_reclaim(rn, list);
 290                local_bh_enable();
 291                list = next;
 292                RCU_TRACE(cb_count++);
 293        }
 294        RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 295        RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
 296                                      is_idle_task(current),
 297                                      rcu_is_callbacks_kthread()));
 298}
 299
 300static void rcu_process_callbacks(struct softirq_action *unused)
 301{
 302        __rcu_process_callbacks(&rcu_sched_ctrlblk);
 303        __rcu_process_callbacks(&rcu_bh_ctrlblk);
 304        rcu_preempt_process_callbacks();
 305}
 306
 307/*
 308 * Wait for a grace period to elapse.  But it is illegal to invoke
 309 * synchronize_sched() from within an RCU read-side critical section.
 310 * Therefore, any legal call to synchronize_sched() is a quiescent
 311 * state, and so on a UP system, synchronize_sched() need do nothing.
 312 * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 313 * benefits of doing might_sleep() to reduce latency.)
 314 *
 315 * Cool, huh?  (Due to Josh Triplett.)
 316 *
 317 * But we want to make this a static inline later.  The cond_resched()
 318 * currently makes this problematic.
 319 */
 320void synchronize_sched(void)
 321{
 322        cond_resched();
 323}
 324EXPORT_SYMBOL_GPL(synchronize_sched);
 325
 326/*
 327 * Helper function for call_rcu() and call_rcu_bh().
 328 */
 329static void __call_rcu(struct rcu_head *head,
 330                       void (*func)(struct rcu_head *rcu),
 331                       struct rcu_ctrlblk *rcp)
 332{
 333        unsigned long flags;
 334
 335        debug_rcu_head_queue(head);
 336        head->func = func;
 337        head->next = NULL;
 338
 339        local_irq_save(flags);
 340        *rcp->curtail = head;
 341        rcp->curtail = &head->next;
 342        RCU_TRACE(rcp->qlen++);
 343        local_irq_restore(flags);
 344}
 345
 346/*
 347 * Post an RCU callback to be invoked after the end of an RCU-sched grace
 348 * period.  But since we have but one CPU, that would be after any
 349 * quiescent state.
 350 */
 351void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 352{
 353        __call_rcu(head, func, &rcu_sched_ctrlblk);
 354}
 355EXPORT_SYMBOL_GPL(call_rcu_sched);
 356
 357/*
 358 * Post an RCU bottom-half callback to be invoked after any subsequent
 359 * quiescent state.
 360 */
 361void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 362{
 363        __call_rcu(head, func, &rcu_bh_ctrlblk);
 364}
 365EXPORT_SYMBOL_GPL(call_rcu_bh);
 366