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
  54static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
  55
  56#include "rcutiny_plugin.h"
  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 */
 196static int 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        reset_cpu_stall_ticks(rcp);
 209        if (rcp->rcucblist != NULL &&
 210            rcp->donetail != rcp->curtail) {
 211                rcp->donetail = rcp->curtail;
 212                return 1;
 213        }
 214
 215        return 0;
 216}
 217
 218/*
 219 * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 220 * are at it, given that any rcu quiescent state is also an rcu_bh
 221 * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 222 */
 223void rcu_sched_qs(int cpu)
 224{
 225        unsigned long flags;
 226
 227        local_irq_save(flags);
 228        if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 229            rcu_qsctr_help(&rcu_bh_ctrlblk))
 230                invoke_rcu_callbacks();
 231        local_irq_restore(flags);
 232}
 233
 234/*
 235 * Record an rcu_bh quiescent state.
 236 */
 237void rcu_bh_qs(int cpu)
 238{
 239        unsigned long flags;
 240
 241        local_irq_save(flags);
 242        if (rcu_qsctr_help(&rcu_bh_ctrlblk))
 243                invoke_rcu_callbacks();
 244        local_irq_restore(flags);
 245}
 246
 247/*
 248 * Check to see if the scheduling-clock interrupt came from an extended
 249 * quiescent state, and, if so, tell RCU about it.  This function must
 250 * be called from hardirq context.  It is normally called from the
 251 * scheduling-clock interrupt.
 252 */
 253void rcu_check_callbacks(int cpu, int user)
 254{
 255        check_cpu_stalls();
 256        if (user || rcu_is_cpu_rrupt_from_idle())
 257                rcu_sched_qs(cpu);
 258        else if (!in_softirq())
 259                rcu_bh_qs(cpu);
 260        rcu_preempt_check_callbacks();
 261}
 262
 263/*
 264 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
 265 * whose grace period has elapsed.
 266 */
 267static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 268{
 269        char *rn = NULL;
 270        struct rcu_head *next, *list;
 271        unsigned long flags;
 272        RCU_TRACE(int cb_count = 0);
 273
 274        /* If no RCU callbacks ready to invoke, just return. */
 275        if (&rcp->rcucblist == rcp->donetail) {
 276                RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
 277                RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
 278                                              ACCESS_ONCE(rcp->rcucblist),
 279                                              need_resched(),
 280                                              is_idle_task(current),
 281                                              rcu_is_callbacks_kthread()));
 282                return;
 283        }
 284
 285        /* Move the ready-to-invoke callbacks to a local list. */
 286        local_irq_save(flags);
 287        RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
 288        list = rcp->rcucblist;
 289        rcp->rcucblist = *rcp->donetail;
 290        *rcp->donetail = NULL;
 291        if (rcp->curtail == rcp->donetail)
 292                rcp->curtail = &rcp->rcucblist;
 293        rcu_preempt_remove_callbacks(rcp);
 294        rcp->donetail = &rcp->rcucblist;
 295        local_irq_restore(flags);
 296
 297        /* Invoke the callbacks on the local list. */
 298        RCU_TRACE(rn = rcp->name);
 299        while (list) {
 300                next = list->next;
 301                prefetch(next);
 302                debug_rcu_head_unqueue(list);
 303                local_bh_disable();
 304                __rcu_reclaim(rn, list);
 305                local_bh_enable();
 306                list = next;
 307                RCU_TRACE(cb_count++);
 308        }
 309        RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 310        RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
 311                                      is_idle_task(current),
 312                                      rcu_is_callbacks_kthread()));
 313}
 314
 315static void rcu_process_callbacks(struct softirq_action *unused)
 316{
 317        __rcu_process_callbacks(&rcu_sched_ctrlblk);
 318        __rcu_process_callbacks(&rcu_bh_ctrlblk);
 319        rcu_preempt_process_callbacks();
 320}
 321
 322/*
 323 * Wait for a grace period to elapse.  But it is illegal to invoke
 324 * synchronize_sched() from within an RCU read-side critical section.
 325 * Therefore, any legal call to synchronize_sched() is a quiescent
 326 * state, and so on a UP system, synchronize_sched() need do nothing.
 327 * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
 328 * benefits of doing might_sleep() to reduce latency.)
 329 *
 330 * Cool, huh?  (Due to Josh Triplett.)
 331 *
 332 * But we want to make this a static inline later.  The cond_resched()
 333 * currently makes this problematic.
 334 */
 335void synchronize_sched(void)
 336{
 337        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 338                           !lock_is_held(&rcu_lock_map) &&
 339                           !lock_is_held(&rcu_sched_lock_map),
 340                           "Illegal synchronize_sched() in RCU read-side critical section");
 341        cond_resched();
 342}
 343EXPORT_SYMBOL_GPL(synchronize_sched);
 344
 345/*
 346 * Helper function for call_rcu() and call_rcu_bh().
 347 */
 348static void __call_rcu(struct rcu_head *head,
 349                       void (*func)(struct rcu_head *rcu),
 350                       struct rcu_ctrlblk *rcp)
 351{
 352        unsigned long flags;
 353
 354        debug_rcu_head_queue(head);
 355        head->func = func;
 356        head->next = NULL;
 357
 358        local_irq_save(flags);
 359        *rcp->curtail = head;
 360        rcp->curtail = &head->next;
 361        RCU_TRACE(rcp->qlen++);
 362        local_irq_restore(flags);
 363}
 364
 365/*
 366 * Post an RCU callback to be invoked after the end of an RCU-sched grace
 367 * period.  But since we have but one CPU, that would be after any
 368 * quiescent state.
 369 */
 370void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 371{
 372        __call_rcu(head, func, &rcu_sched_ctrlblk);
 373}
 374EXPORT_SYMBOL_GPL(call_rcu_sched);
 375
 376/*
 377 * Post an RCU bottom-half callback to be invoked after any subsequent
 378 * quiescent state.
 379 */
 380void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 381{
 382        __call_rcu(head, func, &rcu_bh_ctrlblk);
 383}
 384EXPORT_SYMBOL_GPL(call_rcu_bh);
 385
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