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 __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
  48static void rcu_process_callbacks(struct softirq_action *unused);
  49static void __call_rcu(struct rcu_head *head,
  50                       void (*func)(struct rcu_head *rcu),
  51                       struct rcu_ctrlblk *rcp);
  52
  53static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
  54
  55#include "rcutiny_plugin.h"
  56
  57/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
  58static void rcu_idle_enter_common(long long newval)
  59{
  60        if (newval) {
  61                RCU_TRACE(trace_rcu_dyntick("--=",
  62                                            rcu_dynticks_nesting, newval));
  63                rcu_dynticks_nesting = newval;
  64                return;
  65        }
  66        RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval));
  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                                            rcu_dynticks_nesting, newval));
  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        barrier();
  79        rcu_dynticks_nesting = newval;
  80}
  81
  82/*
  83 * Enter idle, which is an extended quiescent state if we have fully
  84 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
  85 */
  86void rcu_idle_enter(void)
  87{
  88        unsigned long flags;
  89        long long newval;
  90
  91        local_irq_save(flags);
  92        WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
  93        if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
  94            DYNTICK_TASK_NEST_VALUE)
  95                newval = 0;
  96        else
  97                newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
  98        rcu_idle_enter_common(newval);
  99        local_irq_restore(flags);
 100}
 101EXPORT_SYMBOL_GPL(rcu_idle_enter);
 102
 103/*
 104 * Exit an interrupt handler towards idle.
 105 */
 106void rcu_irq_exit(void)
 107{
 108        unsigned long flags;
 109        long long newval;
 110
 111        local_irq_save(flags);
 112        newval = rcu_dynticks_nesting - 1;
 113        WARN_ON_ONCE(newval < 0);
 114        rcu_idle_enter_common(newval);
 115        local_irq_restore(flags);
 116}
 117EXPORT_SYMBOL_GPL(rcu_irq_exit);
 118
 119/* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
 120static void rcu_idle_exit_common(long long oldval)
 121{
 122        if (oldval) {
 123                RCU_TRACE(trace_rcu_dyntick("++=",
 124                                            oldval, rcu_dynticks_nesting));
 125                return;
 126        }
 127        RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
 128        if (!is_idle_task(current)) {
 129                struct task_struct *idle = idle_task(smp_processor_id());
 130
 131                RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
 132                          oldval, rcu_dynticks_nesting));
 133                ftrace_dump(DUMP_ALL);
 134                WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
 135                          current->pid, current->comm,
 136                          idle->pid, idle->comm); /* must be idle task! */
 137        }
 138}
 139
 140/*
 141 * Exit idle, so that we are no longer in an extended quiescent state.
 142 */
 143void rcu_idle_exit(void)
 144{
 145        unsigned long flags;
 146        long long oldval;
 147
 148        local_irq_save(flags);
 149        oldval = rcu_dynticks_nesting;
 150        WARN_ON_ONCE(rcu_dynticks_nesting < 0);
 151        if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
 152                rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
 153        else
 154                rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
 155        rcu_idle_exit_common(oldval);
 156        local_irq_restore(flags);
 157}
 158EXPORT_SYMBOL_GPL(rcu_idle_exit);
 159
 160/*
 161 * Enter an interrupt handler, moving away from idle.
 162 */
 163void rcu_irq_enter(void)
 164{
 165        unsigned long flags;
 166        long long oldval;
 167
 168        local_irq_save(flags);
 169        oldval = rcu_dynticks_nesting;
 170        rcu_dynticks_nesting++;
 171        WARN_ON_ONCE(rcu_dynticks_nesting == 0);
 172        rcu_idle_exit_common(oldval);
 173        local_irq_restore(flags);
 174}
 175EXPORT_SYMBOL_GPL(rcu_irq_enter);
 176
 177#ifdef CONFIG_DEBUG_LOCK_ALLOC
 178
 179/*
 180 * Test whether RCU thinks that the current CPU is idle.
 181 */
 182int rcu_is_cpu_idle(void)
 183{
 184        return !rcu_dynticks_nesting;
 185}
 186EXPORT_SYMBOL(rcu_is_cpu_idle);
 187
 188#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 189
 190/*
 191 * Test whether the current CPU was interrupted from idle.  Nested
 192 * interrupts don't count, we must be running at the first interrupt
 193 * level.
 194 */
 195static int rcu_is_cpu_rrupt_from_idle(void)
 196{
 197        return rcu_dynticks_nesting <= 1;
 198}
 199
 200/*
 201 * Helper function for rcu_sched_qs() and rcu_bh_qs().
 202 * Also irqs are disabled to avoid confusion due to interrupt handlers
 203 * invoking call_rcu().
 204 */
 205static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 206{
 207        RCU_TRACE(reset_cpu_stall_ticks(rcp));
 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                raise_softirq(RCU_SOFTIRQ);
 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                raise_softirq(RCU_SOFTIRQ);
 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        RCU_TRACE(check_cpu_stalls());
 255        if (user || rcu_is_cpu_rrupt_from_idle())
 256                rcu_sched_qs(cpu);
 257        else if (!in_softirq())
 258                rcu_bh_qs(cpu);
 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        const 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                                              false));
 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        rcp->donetail = &rcp->rcucblist;
 292        local_irq_restore(flags);
 293
 294        /* Invoke the callbacks on the local list. */
 295        RCU_TRACE(rn = rcp->name);
 296        while (list) {
 297                next = list->next;
 298                prefetch(next);
 299                debug_rcu_head_unqueue(list);
 300                local_bh_disable();
 301                __rcu_reclaim(rn, list);
 302                local_bh_enable();
 303                list = next;
 304                RCU_TRACE(cb_count++);
 305        }
 306        RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 307        RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
 308                                      is_idle_task(current),
 309                                      false));
 310}
 311
 312static void rcu_process_callbacks(struct softirq_action *unused)
 313{
 314        __rcu_process_callbacks(&rcu_sched_ctrlblk);
 315        __rcu_process_callbacks(&rcu_bh_ctrlblk);
 316}
 317
 318/*
 319 * Wait for a grace period to elapse.  But it is illegal to invoke
 320 * synchronize_sched() from within an RCU read-side critical section.
 321 * Therefore, any legal call to synchronize_sched() is a quiescent
 322 * state, and so on a UP system, synchronize_sched() need do nothing.
 323 * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 324 * benefits of doing might_sleep() to reduce latency.)
 325 *
 326 * Cool, huh?  (Due to Josh Triplett.)
 327 *
 328 * But we want to make this a static inline later.  The cond_resched()
 329 * currently makes this problematic.
 330 */
 331void synchronize_sched(void)
 332{
 333        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 334                           !lock_is_held(&rcu_lock_map) &&
 335                           !lock_is_held(&rcu_sched_lock_map),
 336                           "Illegal synchronize_sched() in RCU read-side critical section");
 337        cond_resched();
 338}
 339EXPORT_SYMBOL_GPL(synchronize_sched);
 340
 341/*
 342 * Helper function for call_rcu() and call_rcu_bh().
 343 */
 344static void __call_rcu(struct rcu_head *head,
 345                       void (*func)(struct rcu_head *rcu),
 346                       struct rcu_ctrlblk *rcp)
 347{
 348        unsigned long flags;
 349
 350        debug_rcu_head_queue(head);
 351        head->func = func;
 352        head->next = NULL;
 353
 354        local_irq_save(flags);
 355        *rcp->curtail = head;
 356        rcp->curtail = &head->next;
 357        RCU_TRACE(rcp->qlen++);
 358        local_irq_restore(flags);
 359}
 360
 361/*
 362 * Post an RCU callback to be invoked after the end of an RCU-sched grace
 363 * period.  But since we have but one CPU, that would be after any
 364 * quiescent state.
 365 */
 366void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 367{
 368        __call_rcu(head, func, &rcu_sched_ctrlblk);
 369}
 370EXPORT_SYMBOL_GPL(call_rcu_sched);
 371
 372/*
 373 * Post an RCU bottom-half callback to be invoked after any subsequent
 374 * quiescent state.
 375 */
 376void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 377{
 378        __call_rcu(head, func, &rcu_bh_ctrlblk);
 379}
 380EXPORT_SYMBOL_GPL(call_rcu_bh);
 381
 382void rcu_init(void)
 383{
 384        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 385}
 386
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