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