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_EXIT_IDLE;
  57
  58/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
  59static void rcu_idle_enter_common(long long newval)
  60{
  61        if (newval) {
  62                RCU_TRACE(trace_rcu_dyntick("--=",
  63                                            rcu_dynticks_nesting, newval));
  64                rcu_dynticks_nesting = newval;
  65                return;
  66        }
  67        RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
  68        if (!is_idle_task(current)) {
  69                struct task_struct *idle = idle_task(smp_processor_id());
  70
  71                RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
  72                                            rcu_dynticks_nesting, newval));
  73                ftrace_dump(DUMP_ALL);
  74                WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
  75                          current->pid, current->comm,
  76                          idle->pid, idle->comm); /* must be idle task! */
  77        }
  78        rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
  79        barrier();
  80        rcu_dynticks_nesting = newval;
  81}
  82
  83/*
  84 * Enter idle, which is an extended quiescent state if we have fully
  85 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
  86 */
  87void rcu_idle_enter(void)
  88{
  89        unsigned long flags;
  90        long long newval;
  91
  92        local_irq_save(flags);
  93        WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
  94        if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
  95            DYNTICK_TASK_NEST_VALUE)
  96                newval = 0;
  97        else
  98                newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
  99        rcu_idle_enter_common(newval);
 100        local_irq_restore(flags);
 101}
 102EXPORT_SYMBOL_GPL(rcu_idle_enter);
 103
 104/*
 105 * Exit an interrupt handler towards idle.
 106 */
 107void rcu_irq_exit(void)
 108{
 109        unsigned long flags;
 110        long long newval;
 111
 112        local_irq_save(flags);
 113        newval = rcu_dynticks_nesting - 1;
 114        WARN_ON_ONCE(newval < 0);
 115        rcu_idle_enter_common(newval);
 116        local_irq_restore(flags);
 117}
 118EXPORT_SYMBOL_GPL(rcu_irq_exit);
 119
 120/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
 121static void rcu_idle_exit_common(long long oldval)
 122{
 123        if (oldval) {
 124                RCU_TRACE(trace_rcu_dyntick("++=",
 125                                            oldval, rcu_dynticks_nesting));
 126                return;
 127        }
 128        RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
 129        if (!is_idle_task(current)) {
 130                struct task_struct *idle = idle_task(smp_processor_id());
 131
 132                RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
 133                          oldval, rcu_dynticks_nesting));
 134                ftrace_dump(DUMP_ALL);
 135                WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
 136                          current->pid, current->comm,
 137                          idle->pid, idle->comm); /* must be idle task! */
 138        }
 139}
 140
 141/*
 142 * Exit idle, so that we are no longer in an extended quiescent state.
 143 */
 144void rcu_idle_exit(void)
 145{
 146        unsigned long flags;
 147        long long oldval;
 148
 149        local_irq_save(flags);
 150        oldval = rcu_dynticks_nesting;
 151        WARN_ON_ONCE(rcu_dynticks_nesting < 0);
 152        if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
 153                rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
 154        else
 155                rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 156        rcu_idle_exit_common(oldval);
 157        local_irq_restore(flags);
 158}
 159EXPORT_SYMBOL_GPL(rcu_idle_exit);
 160
 161/*
 162 * Enter an interrupt handler, moving away from idle.
 163 */
 164void rcu_irq_enter(void)
 165{
 166        unsigned long flags;
 167        long long oldval;
 168
 169        local_irq_save(flags);
 170        oldval = rcu_dynticks_nesting;
 171        rcu_dynticks_nesting++;
 172        WARN_ON_ONCE(rcu_dynticks_nesting == 0);
 173        rcu_idle_exit_common(oldval);
 174        local_irq_restore(flags);
 175}
 176EXPORT_SYMBOL_GPL(rcu_irq_enter);
 177
 178#ifdef CONFIG_DEBUG_LOCK_ALLOC
 179
 180/*
 181 * Test whether RCU thinks that the current CPU is idle.
 182 */
 183int rcu_is_cpu_idle(void)
 184{
 185        return !rcu_dynticks_nesting;
 186}
 187EXPORT_SYMBOL(rcu_is_cpu_idle);
 188
 189#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 190
 191/*
 192 * Test whether the current CPU was interrupted from idle.  Nested
 193 * interrupts don't count, we must be running at the first interrupt
 194 * level.
 195 */
 196int rcu_is_cpu_rrupt_from_idle(void)
 197{
 198        return rcu_dynticks_nesting <= 1;
 199}
 200
 201/*
 202 * Helper function for rcu_sched_qs() and rcu_bh_qs().
 203 * Also irqs are disabled to avoid confusion due to interrupt handlers
 204 * invoking call_rcu().
 205 */
 206static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 207{
 208        if (rcp->rcucblist != NULL &&
 209            rcp->donetail != rcp->curtail) {
 210                rcp->donetail = rcp->curtail;
 211                return 1;
 212        }
 213
 214        return 0;
 215}
 216
 217/*
 218 * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 219 * are at it, given that any rcu quiescent state is also an rcu_bh
 220 * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 221 */
 222void rcu_sched_qs(int cpu)
 223{
 224        unsigned long flags;
 225
 226        local_irq_save(flags);
 227        if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 228            rcu_qsctr_help(&rcu_bh_ctrlblk))
 229                invoke_rcu_callbacks();
 230        local_irq_restore(flags);
 231}
 232
 233/*
 234 * Record an rcu_bh quiescent state.
 235 */
 236void rcu_bh_qs(int cpu)
 237{
 238        unsigned long flags;
 239
 240        local_irq_save(flags);
 241        if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 242                invoke_rcu_callbacks();
 243        local_irq_restore(flags);
 244}
 245
 246/*
 247 * Check to see if the scheduling-clock interrupt came from an extended
 248 * quiescent state, and, if so, tell RCU about it.  This function must
 249 * be called from hardirq context.  It is normally called from the
 250 * scheduling-clock interrupt.
 251 */
 252void rcu_check_callbacks(int cpu, int user)
 253{
 254        if (user || rcu_is_cpu_rrupt_from_idle())
 255                rcu_sched_qs(cpu);
 256        else if (!in_softirq())
 257                rcu_bh_qs(cpu);
 258        rcu_preempt_check_callbacks();
 259}
 260
 261/*
 262 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 263 * whose grace period has elapsed.
 264 */
 265static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 266{
 267        char *rn = NULL;
 268        struct rcu_head *next, *list;
 269        unsigned long flags;
 270        RCU_TRACE(int cb_count = 0);
 271
 272        /* If no RCU callbacks ready to invoke, just return. */
 273        if (&rcp->rcucblist == rcp->donetail) {
 274                RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
 275                RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
 276                                              ACCESS_ONCE(rcp->rcucblist),
 277                                              need_resched(),
 278                                              is_idle_task(current),
 279                                              rcu_is_callbacks_kthread()));
 280                return;
 281        }
 282
 283        /* Move the ready-to-invoke callbacks to a local list. */
 284        local_irq_save(flags);
 285        RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 286        list = rcp->rcucblist;
 287        rcp->rcucblist = *rcp->donetail;
 288        *rcp->donetail = NULL;
 289        if (rcp->curtail == rcp->donetail)
 290                rcp->curtail = &rcp->rcucblist;
 291        rcu_preempt_remove_callbacks(rcp);
 292        rcp->donetail = &rcp->rcucblist;
 293        local_irq_restore(flags);
 294
 295        /* Invoke the callbacks on the local list. */
 296        RCU_TRACE(rn = rcp->name);
 297        while (list) {
 298                next = list->next;
 299                prefetch(next);
 300                debug_rcu_head_unqueue(list);
 301                local_bh_disable();
 302                __rcu_reclaim(rn, list);
 303                local_bh_enable();
 304                list = next;
 305                RCU_TRACE(cb_count++);
 306        }
 307        RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 308        RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
 309                                      is_idle_task(current),
 310                                      rcu_is_callbacks_kthread()));
 311}
 312
 313static void rcu_process_callbacks(struct softirq_action *unused)
 314{
 315        __rcu_process_callbacks(&rcu_sched_ctrlblk);
 316        __rcu_process_callbacks(&rcu_bh_ctrlblk);
 317        rcu_preempt_process_callbacks();
 318}
 319
 320/*
 321 * Wait for a grace period to elapse.  But it is illegal to invoke
 322 * synchronize_sched() from within an RCU read-side critical section.
 323 * Therefore, any legal call to synchronize_sched() is a quiescent
 324 * state, and so on a UP system, synchronize_sched() need do nothing.
 325 * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 326 * benefits of doing might_sleep() to reduce latency.)
 327 *
 328 * Cool, huh?  (Due to Josh Triplett.)
 329 *
 330 * But we want to make this a static inline later.  The cond_resched()
 331 * currently makes this problematic.
 332 */
 333void synchronize_sched(void)
 334{
 335        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 336                           !lock_is_held(&rcu_lock_map) &&
 337                           !lock_is_held(&rcu_sched_lock_map),
 338                           "Illegal synchronize_sched() in RCU read-side critical section");
 339        cond_resched();
 340}
 341EXPORT_SYMBOL_GPL(synchronize_sched);
 342
 343/*
 344 * Helper function for call_rcu() and call_rcu_bh().
 345 */
 346static void __call_rcu(struct rcu_head *head,
 347                       void (*func)(struct rcu_head *rcu),
 348                       struct rcu_ctrlblk *rcp)
 349{
 350        unsigned long flags;
 351
 352        debug_rcu_head_queue(head);
 353        head->func = func;
 354        head->next = NULL;
 355
 356        local_irq_save(flags);
 357        *rcp->curtail = head;
 358        rcp->curtail = &head->next;
 359        RCU_TRACE(rcp->qlen++);
 360        local_irq_restore(flags);
 361}
 362
 363/*
 364 * Post an RCU callback to be invoked after the end of an RCU-sched grace
 365 * period.  But since we have but one CPU, that would be after any
 366 * quiescent state.
 367 */
 368void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 369{
 370        __call_rcu(head, func, &rcu_sched_ctrlblk);
 371}
 372EXPORT_SYMBOL_GPL(call_rcu_sched);
 373
 374/*
 375 * Post an RCU bottom-half callback to be invoked after any subsequent
 376 * quiescent state.
 377 */
 378void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 379{
 380        __call_rcu(head, func, &rcu_bh_ctrlblk);
 381}
 382EXPORT_SYMBOL_GPL(call_rcu_bh);
 383
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