linux/kernel/rcutree_plugin.h
<<
>>
Prefs
   1/*
   2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
   3 * Internal non-public definitions that provide either classic
   4 * or preemptible semantics.
   5 *
   6 * This program is free software; you can redistribute it and/or modify
   7 * it under the terms of the GNU General Public License as published by
   8 * the Free Software Foundation; either version 2 of the License, or
   9 * (at your option) any later version.
  10 *
  11 * This program is distributed in the hope that it will be useful,
  12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 * GNU General Public License for more details.
  15 *
  16 * You should have received a copy of the GNU General Public License
  17 * along with this program; if not, write to the Free Software
  18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  19 *
  20 * Copyright Red Hat, 2009
  21 * Copyright IBM Corporation, 2009
  22 *
  23 * Author: Ingo Molnar <mingo@elte.hu>
  24 *         Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  25 */
  26
  27#include <linux/delay.h>
  28
  29#define RCU_KTHREAD_PRIO 1
  30
  31#ifdef CONFIG_RCU_BOOST
  32#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
  33#else
  34#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
  35#endif
  36
  37/*
  38 * Check the RCU kernel configuration parameters and print informative
  39 * messages about anything out of the ordinary.  If you like #ifdef, you
  40 * will love this function.
  41 */
  42static void __init rcu_bootup_announce_oddness(void)
  43{
  44#ifdef CONFIG_RCU_TRACE
  45        printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
  46#endif
  47#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
  48        printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
  49               CONFIG_RCU_FANOUT);
  50#endif
  51#ifdef CONFIG_RCU_FANOUT_EXACT
  52        printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
  53#endif
  54#ifdef CONFIG_RCU_FAST_NO_HZ
  55        printk(KERN_INFO
  56               "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
  57#endif
  58#ifdef CONFIG_PROVE_RCU
  59        printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
  60#endif
  61#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
  62        printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
  63#endif
  64#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
  65        printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
  66#endif
  67#if defined(CONFIG_RCU_CPU_STALL_INFO)
  68        printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
  69#endif
  70#if NUM_RCU_LVL_4 != 0
  71        printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n");
  72#endif
  73}
  74
  75#ifdef CONFIG_TREE_PREEMPT_RCU
  76
  77struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt);
  78DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
  79static struct rcu_state *rcu_state = &rcu_preempt_state;
  80
  81static void rcu_read_unlock_special(struct task_struct *t);
  82static int rcu_preempted_readers_exp(struct rcu_node *rnp);
  83
  84/*
  85 * Tell them what RCU they are running.
  86 */
  87static void __init rcu_bootup_announce(void)
  88{
  89        printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
  90        rcu_bootup_announce_oddness();
  91}
  92
  93/*
  94 * Return the number of RCU-preempt batches processed thus far
  95 * for debug and statistics.
  96 */
  97long rcu_batches_completed_preempt(void)
  98{
  99        return rcu_preempt_state.completed;
 100}
 101EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
 102
 103/*
 104 * Return the number of RCU batches processed thus far for debug & stats.
 105 */
 106long rcu_batches_completed(void)
 107{
 108        return rcu_batches_completed_preempt();
 109}
 110EXPORT_SYMBOL_GPL(rcu_batches_completed);
 111
 112/*
 113 * Force a quiescent state for preemptible RCU.
 114 */
 115void rcu_force_quiescent_state(void)
 116{
 117        force_quiescent_state(&rcu_preempt_state, 0);
 118}
 119EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
 120
 121/*
 122 * Record a preemptible-RCU quiescent state for the specified CPU.  Note
 123 * that this just means that the task currently running on the CPU is
 124 * not in a quiescent state.  There might be any number of tasks blocked
 125 * while in an RCU read-side critical section.
 126 *
 127 * Unlike the other rcu_*_qs() functions, callers to this function
 128 * must disable irqs in order to protect the assignment to
 129 * ->rcu_read_unlock_special.
 130 */
 131static void rcu_preempt_qs(int cpu)
 132{
 133        struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
 134
 135        rdp->passed_quiesce_gpnum = rdp->gpnum;
 136        barrier();
 137        if (rdp->passed_quiesce == 0)
 138                trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
 139        rdp->passed_quiesce = 1;
 140        current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
 141}
 142
 143/*
 144 * We have entered the scheduler, and the current task might soon be
 145 * context-switched away from.  If this task is in an RCU read-side
 146 * critical section, we will no longer be able to rely on the CPU to
 147 * record that fact, so we enqueue the task on the blkd_tasks list.
 148 * The task will dequeue itself when it exits the outermost enclosing
 149 * RCU read-side critical section.  Therefore, the current grace period
 150 * cannot be permitted to complete until the blkd_tasks list entries
 151 * predating the current grace period drain, in other words, until
 152 * rnp->gp_tasks becomes NULL.
 153 *
 154 * Caller must disable preemption.
 155 */
 156static void rcu_preempt_note_context_switch(int cpu)
 157{
 158        struct task_struct *t = current;
 159        unsigned long flags;
 160        struct rcu_data *rdp;
 161        struct rcu_node *rnp;
 162
 163        if (t->rcu_read_lock_nesting > 0 &&
 164            (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 165
 166                /* Possibly blocking in an RCU read-side critical section. */
 167                rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
 168                rnp = rdp->mynode;
 169                raw_spin_lock_irqsave(&rnp->lock, flags);
 170                t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
 171                t->rcu_blocked_node = rnp;
 172
 173                /*
 174                 * If this CPU has already checked in, then this task
 175                 * will hold up the next grace period rather than the
 176                 * current grace period.  Queue the task accordingly.
 177                 * If the task is queued for the current grace period
 178                 * (i.e., this CPU has not yet passed through a quiescent
 179                 * state for the current grace period), then as long
 180                 * as that task remains queued, the current grace period
 181                 * cannot end.  Note that there is some uncertainty as
 182                 * to exactly when the current grace period started.
 183                 * We take a conservative approach, which can result
 184                 * in unnecessarily waiting on tasks that started very
 185                 * slightly after the current grace period began.  C'est
 186                 * la vie!!!
 187                 *
 188                 * But first, note that the current CPU must still be
 189                 * on line!
 190                 */
 191                WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
 192                WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
 193                if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
 194                        list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
 195                        rnp->gp_tasks = &t->rcu_node_entry;
 196#ifdef CONFIG_RCU_BOOST
 197                        if (rnp->boost_tasks != NULL)
 198                                rnp->boost_tasks = rnp->gp_tasks;
 199#endif /* #ifdef CONFIG_RCU_BOOST */
 200                } else {
 201                        list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
 202                        if (rnp->qsmask & rdp->grpmask)
 203                                rnp->gp_tasks = &t->rcu_node_entry;
 204                }
 205                trace_rcu_preempt_task(rdp->rsp->name,
 206                                       t->pid,
 207                                       (rnp->qsmask & rdp->grpmask)
 208                                       ? rnp->gpnum
 209                                       : rnp->gpnum + 1);
 210                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 211        } else if (t->rcu_read_lock_nesting < 0 &&
 212                   t->rcu_read_unlock_special) {
 213
 214                /*
 215                 * Complete exit from RCU read-side critical section on
 216                 * behalf of preempted instance of __rcu_read_unlock().
 217                 */
 218                rcu_read_unlock_special(t);
 219        }
 220
 221        /*
 222         * Either we were not in an RCU read-side critical section to
 223         * begin with, or we have now recorded that critical section
 224         * globally.  Either way, we can now note a quiescent state
 225         * for this CPU.  Again, if we were in an RCU read-side critical
 226         * section, and if that critical section was blocking the current
 227         * grace period, then the fact that the task has been enqueued
 228         * means that we continue to block the current grace period.
 229         */
 230        local_irq_save(flags);
 231        rcu_preempt_qs(cpu);
 232        local_irq_restore(flags);
 233}
 234
 235/*
 236 * Tree-preemptible RCU implementation for rcu_read_lock().
 237 * Just increment ->rcu_read_lock_nesting, shared state will be updated
 238 * if we block.
 239 */
 240void __rcu_read_lock(void)
 241{
 242        current->rcu_read_lock_nesting++;
 243        barrier();  /* needed if we ever invoke rcu_read_lock in rcutree.c */
 244}
 245EXPORT_SYMBOL_GPL(__rcu_read_lock);
 246
 247/*
 248 * Check for preempted RCU readers blocking the current grace period
 249 * for the specified rcu_node structure.  If the caller needs a reliable
 250 * answer, it must hold the rcu_node's ->lock.
 251 */
 252static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
 253{
 254        return rnp->gp_tasks != NULL;
 255}
 256
 257/*
 258 * Record a quiescent state for all tasks that were previously queued
 259 * on the specified rcu_node structure and that were blocking the current
 260 * RCU grace period.  The caller must hold the specified rnp->lock with
 261 * irqs disabled, and this lock is released upon return, but irqs remain
 262 * disabled.
 263 */
 264static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
 265        __releases(rnp->lock)
 266{
 267        unsigned long mask;
 268        struct rcu_node *rnp_p;
 269
 270        if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
 271                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 272                return;  /* Still need more quiescent states! */
 273        }
 274
 275        rnp_p = rnp->parent;
 276        if (rnp_p == NULL) {
 277                /*
 278                 * Either there is only one rcu_node in the tree,
 279                 * or tasks were kicked up to root rcu_node due to
 280                 * CPUs going offline.
 281                 */
 282                rcu_report_qs_rsp(&rcu_preempt_state, flags);
 283                return;
 284        }
 285
 286        /* Report up the rest of the hierarchy. */
 287        mask = rnp->grpmask;
 288        raw_spin_unlock(&rnp->lock);    /* irqs remain disabled. */
 289        raw_spin_lock(&rnp_p->lock);    /* irqs already disabled. */
 290        rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
 291}
 292
 293/*
 294 * Advance a ->blkd_tasks-list pointer to the next entry, instead
 295 * returning NULL if at the end of the list.
 296 */
 297static struct list_head *rcu_next_node_entry(struct task_struct *t,
 298                                             struct rcu_node *rnp)
 299{
 300        struct list_head *np;
 301
 302        np = t->rcu_node_entry.next;
 303        if (np == &rnp->blkd_tasks)
 304                np = NULL;
 305        return np;
 306}
 307
 308/*
 309 * Handle special cases during rcu_read_unlock(), such as needing to
 310 * notify RCU core processing or task having blocked during the RCU
 311 * read-side critical section.
 312 */
 313static noinline void rcu_read_unlock_special(struct task_struct *t)
 314{
 315        int empty;
 316        int empty_exp;
 317        int empty_exp_now;
 318        unsigned long flags;
 319        struct list_head *np;
 320#ifdef CONFIG_RCU_BOOST
 321        struct rt_mutex *rbmp = NULL;
 322#endif /* #ifdef CONFIG_RCU_BOOST */
 323        struct rcu_node *rnp;
 324        int special;
 325
 326        /* NMI handlers cannot block and cannot safely manipulate state. */
 327        if (in_nmi())
 328                return;
 329
 330        local_irq_save(flags);
 331
 332        /*
 333         * If RCU core is waiting for this CPU to exit critical section,
 334         * let it know that we have done so.
 335         */
 336        special = t->rcu_read_unlock_special;
 337        if (special & RCU_READ_UNLOCK_NEED_QS) {
 338                rcu_preempt_qs(smp_processor_id());
 339        }
 340
 341        /* Hardware IRQ handlers cannot block. */
 342        if (in_irq() || in_serving_softirq()) {
 343                local_irq_restore(flags);
 344                return;
 345        }
 346
 347        /* Clean up if blocked during RCU read-side critical section. */
 348        if (special & RCU_READ_UNLOCK_BLOCKED) {
 349                t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
 350
 351                /*
 352                 * Remove this task from the list it blocked on.  The
 353                 * task can migrate while we acquire the lock, but at
 354                 * most one time.  So at most two passes through loop.
 355                 */
 356                for (;;) {
 357                        rnp = t->rcu_blocked_node;
 358                        raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
 359                        if (rnp == t->rcu_blocked_node)
 360                                break;
 361                        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
 362                }
 363                empty = !rcu_preempt_blocked_readers_cgp(rnp);
 364                empty_exp = !rcu_preempted_readers_exp(rnp);
 365                smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
 366                np = rcu_next_node_entry(t, rnp);
 367                list_del_init(&t->rcu_node_entry);
 368                t->rcu_blocked_node = NULL;
 369                trace_rcu_unlock_preempted_task("rcu_preempt",
 370                                                rnp->gpnum, t->pid);
 371                if (&t->rcu_node_entry == rnp->gp_tasks)
 372                        rnp->gp_tasks = np;
 373                if (&t->rcu_node_entry == rnp->exp_tasks)
 374                        rnp->exp_tasks = np;
 375#ifdef CONFIG_RCU_BOOST
 376                if (&t->rcu_node_entry == rnp->boost_tasks)
 377                        rnp->boost_tasks = np;
 378                /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
 379                if (t->rcu_boost_mutex) {
 380                        rbmp = t->rcu_boost_mutex;
 381                        t->rcu_boost_mutex = NULL;
 382                }
 383#endif /* #ifdef CONFIG_RCU_BOOST */
 384
 385                /*
 386                 * If this was the last task on the current list, and if
 387                 * we aren't waiting on any CPUs, report the quiescent state.
 388                 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
 389                 * so we must take a snapshot of the expedited state.
 390                 */
 391                empty_exp_now = !rcu_preempted_readers_exp(rnp);
 392                if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
 393                        trace_rcu_quiescent_state_report("preempt_rcu",
 394                                                         rnp->gpnum,
 395                                                         0, rnp->qsmask,
 396                                                         rnp->level,
 397                                                         rnp->grplo,
 398                                                         rnp->grphi,
 399                                                         !!rnp->gp_tasks);
 400                        rcu_report_unblock_qs_rnp(rnp, flags);
 401                } else
 402                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 403
 404#ifdef CONFIG_RCU_BOOST
 405                /* Unboost if we were boosted. */
 406                if (rbmp)
 407                        rt_mutex_unlock(rbmp);
 408#endif /* #ifdef CONFIG_RCU_BOOST */
 409
 410                /*
 411                 * If this was the last task on the expedited lists,
 412                 * then we need to report up the rcu_node hierarchy.
 413                 */
 414                if (!empty_exp && empty_exp_now)
 415                        rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
 416        } else {
 417                local_irq_restore(flags);
 418        }
 419}
 420
 421/*
 422 * Tree-preemptible RCU implementation for rcu_read_unlock().
 423 * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
 424 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
 425 * invoke rcu_read_unlock_special() to clean up after a context switch
 426 * in an RCU read-side critical section and other special cases.
 427 */
 428void __rcu_read_unlock(void)
 429{
 430        struct task_struct *t = current;
 431
 432        if (t->rcu_read_lock_nesting != 1)
 433                --t->rcu_read_lock_nesting;
 434        else {
 435                barrier();  /* critical section before exit code. */
 436                t->rcu_read_lock_nesting = INT_MIN;
 437                barrier();  /* assign before ->rcu_read_unlock_special load */
 438                if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
 439                        rcu_read_unlock_special(t);
 440                barrier();  /* ->rcu_read_unlock_special load before assign */
 441                t->rcu_read_lock_nesting = 0;
 442        }
 443#ifdef CONFIG_PROVE_LOCKING
 444        {
 445                int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
 446
 447                WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
 448        }
 449#endif /* #ifdef CONFIG_PROVE_LOCKING */
 450}
 451EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 452
 453#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
 454
 455/*
 456 * Dump detailed information for all tasks blocking the current RCU
 457 * grace period on the specified rcu_node structure.
 458 */
 459static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
 460{
 461        unsigned long flags;
 462        struct task_struct *t;
 463
 464        if (!rcu_preempt_blocked_readers_cgp(rnp))
 465                return;
 466        raw_spin_lock_irqsave(&rnp->lock, flags);
 467        t = list_entry(rnp->gp_tasks,
 468                       struct task_struct, rcu_node_entry);
 469        list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
 470                sched_show_task(t);
 471        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 472}
 473
 474/*
 475 * Dump detailed information for all tasks blocking the current RCU
 476 * grace period.
 477 */
 478static void rcu_print_detail_task_stall(struct rcu_state *rsp)
 479{
 480        struct rcu_node *rnp = rcu_get_root(rsp);
 481
 482        rcu_print_detail_task_stall_rnp(rnp);
 483        rcu_for_each_leaf_node(rsp, rnp)
 484                rcu_print_detail_task_stall_rnp(rnp);
 485}
 486
 487#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
 488
 489static void rcu_print_detail_task_stall(struct rcu_state *rsp)
 490{
 491}
 492
 493#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
 494
 495#ifdef CONFIG_RCU_CPU_STALL_INFO
 496
 497static void rcu_print_task_stall_begin(struct rcu_node *rnp)
 498{
 499        printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
 500               rnp->level, rnp->grplo, rnp->grphi);
 501}
 502
 503static void rcu_print_task_stall_end(void)
 504{
 505        printk(KERN_CONT "\n");
 506}
 507
 508#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
 509
 510static void rcu_print_task_stall_begin(struct rcu_node *rnp)
 511{
 512}
 513
 514static void rcu_print_task_stall_end(void)
 515{
 516}
 517
 518#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
 519
 520/*
 521 * Scan the current list of tasks blocked within RCU read-side critical
 522 * sections, printing out the tid of each.
 523 */
 524static int rcu_print_task_stall(struct rcu_node *rnp)
 525{
 526        struct task_struct *t;
 527        int ndetected = 0;
 528
 529        if (!rcu_preempt_blocked_readers_cgp(rnp))
 530                return 0;
 531        rcu_print_task_stall_begin(rnp);
 532        t = list_entry(rnp->gp_tasks,
 533                       struct task_struct, rcu_node_entry);
 534        list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 535                printk(KERN_CONT " P%d", t->pid);
 536                ndetected++;
 537        }
 538        rcu_print_task_stall_end();
 539        return ndetected;
 540}
 541
 542/*
 543 * Suppress preemptible RCU's CPU stall warnings by pushing the
 544 * time of the next stall-warning message comfortably far into the
 545 * future.
 546 */
 547static void rcu_preempt_stall_reset(void)
 548{
 549        rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
 550}
 551
 552/*
 553 * Check that the list of blocked tasks for the newly completed grace
 554 * period is in fact empty.  It is a serious bug to complete a grace
 555 * period that still has RCU readers blocked!  This function must be
 556 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
 557 * must be held by the caller.
 558 *
 559 * Also, if there are blocked tasks on the list, they automatically
 560 * block the newly created grace period, so set up ->gp_tasks accordingly.
 561 */
 562static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
 563{
 564        WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
 565        if (!list_empty(&rnp->blkd_tasks))
 566                rnp->gp_tasks = rnp->blkd_tasks.next;
 567        WARN_ON_ONCE(rnp->qsmask);
 568}
 569
 570#ifdef CONFIG_HOTPLUG_CPU
 571
 572/*
 573 * Handle tasklist migration for case in which all CPUs covered by the
 574 * specified rcu_node have gone offline.  Move them up to the root
 575 * rcu_node.  The reason for not just moving them to the immediate
 576 * parent is to remove the need for rcu_read_unlock_special() to
 577 * make more than two attempts to acquire the target rcu_node's lock.
 578 * Returns true if there were tasks blocking the current RCU grace
 579 * period.
 580 *
 581 * Returns 1 if there was previously a task blocking the current grace
 582 * period on the specified rcu_node structure.
 583 *
 584 * The caller must hold rnp->lock with irqs disabled.
 585 */
 586static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
 587                                     struct rcu_node *rnp,
 588                                     struct rcu_data *rdp)
 589{
 590        struct list_head *lp;
 591        struct list_head *lp_root;
 592        int retval = 0;
 593        struct rcu_node *rnp_root = rcu_get_root(rsp);
 594        struct task_struct *t;
 595
 596        if (rnp == rnp_root) {
 597                WARN_ONCE(1, "Last CPU thought to be offlined?");
 598                return 0;  /* Shouldn't happen: at least one CPU online. */
 599        }
 600
 601        /* If we are on an internal node, complain bitterly. */
 602        WARN_ON_ONCE(rnp != rdp->mynode);
 603
 604        /*
 605         * Move tasks up to root rcu_node.  Don't try to get fancy for
 606         * this corner-case operation -- just put this node's tasks
 607         * at the head of the root node's list, and update the root node's
 608         * ->gp_tasks and ->exp_tasks pointers to those of this node's,
 609         * if non-NULL.  This might result in waiting for more tasks than
 610         * absolutely necessary, but this is a good performance/complexity
 611         * tradeoff.
 612         */
 613        if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
 614                retval |= RCU_OFL_TASKS_NORM_GP;
 615        if (rcu_preempted_readers_exp(rnp))
 616                retval |= RCU_OFL_TASKS_EXP_GP;
 617        lp = &rnp->blkd_tasks;
 618        lp_root = &rnp_root->blkd_tasks;
 619        while (!list_empty(lp)) {
 620                t = list_entry(lp->next, typeof(*t), rcu_node_entry);
 621                raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
 622                list_del(&t->rcu_node_entry);
 623                t->rcu_blocked_node = rnp_root;
 624                list_add(&t->rcu_node_entry, lp_root);
 625                if (&t->rcu_node_entry == rnp->gp_tasks)
 626                        rnp_root->gp_tasks = rnp->gp_tasks;
 627                if (&t->rcu_node_entry == rnp->exp_tasks)
 628                        rnp_root->exp_tasks = rnp->exp_tasks;
 629#ifdef CONFIG_RCU_BOOST
 630                if (&t->rcu_node_entry == rnp->boost_tasks)
 631                        rnp_root->boost_tasks = rnp->boost_tasks;
 632#endif /* #ifdef CONFIG_RCU_BOOST */
 633                raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
 634        }
 635
 636#ifdef CONFIG_RCU_BOOST
 637        /* In case root is being boosted and leaf is not. */
 638        raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
 639        if (rnp_root->boost_tasks != NULL &&
 640            rnp_root->boost_tasks != rnp_root->gp_tasks)
 641                rnp_root->boost_tasks = rnp_root->gp_tasks;
 642        raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
 643#endif /* #ifdef CONFIG_RCU_BOOST */
 644
 645        rnp->gp_tasks = NULL;
 646        rnp->exp_tasks = NULL;
 647        return retval;
 648}
 649
 650#endif /* #ifdef CONFIG_HOTPLUG_CPU */
 651
 652/*
 653 * Do CPU-offline processing for preemptible RCU.
 654 */
 655static void rcu_preempt_cleanup_dead_cpu(int cpu)
 656{
 657        rcu_cleanup_dead_cpu(cpu, &rcu_preempt_state);
 658}
 659
 660/*
 661 * Check for a quiescent state from the current CPU.  When a task blocks,
 662 * the task is recorded in the corresponding CPU's rcu_node structure,
 663 * which is checked elsewhere.
 664 *
 665 * Caller must disable hard irqs.
 666 */
 667static void rcu_preempt_check_callbacks(int cpu)
 668{
 669        struct task_struct *t = current;
 670
 671        if (t->rcu_read_lock_nesting == 0) {
 672                rcu_preempt_qs(cpu);
 673                return;
 674        }
 675        if (t->rcu_read_lock_nesting > 0 &&
 676            per_cpu(rcu_preempt_data, cpu).qs_pending)
 677                t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 678}
 679
 680/*
 681 * Process callbacks for preemptible RCU.
 682 */
 683static void rcu_preempt_process_callbacks(void)
 684{
 685        __rcu_process_callbacks(&rcu_preempt_state,
 686                                &__get_cpu_var(rcu_preempt_data));
 687}
 688
 689#ifdef CONFIG_RCU_BOOST
 690
 691static void rcu_preempt_do_callbacks(void)
 692{
 693        rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
 694}
 695
 696#endif /* #ifdef CONFIG_RCU_BOOST */
 697
 698/*
 699 * Queue a preemptible-RCU callback for invocation after a grace period.
 700 */
 701void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 702{
 703        __call_rcu(head, func, &rcu_preempt_state, 0);
 704}
 705EXPORT_SYMBOL_GPL(call_rcu);
 706
 707/*
 708 * Queue an RCU callback for lazy invocation after a grace period.
 709 * This will likely be later named something like "call_rcu_lazy()",
 710 * but this change will require some way of tagging the lazy RCU
 711 * callbacks in the list of pending callbacks.  Until then, this
 712 * function may only be called from __kfree_rcu().
 713 */
 714void kfree_call_rcu(struct rcu_head *head,
 715                    void (*func)(struct rcu_head *rcu))
 716{
 717        __call_rcu(head, func, &rcu_preempt_state, 1);
 718}
 719EXPORT_SYMBOL_GPL(kfree_call_rcu);
 720
 721/**
 722 * synchronize_rcu - wait until a grace period has elapsed.
 723 *
 724 * Control will return to the caller some time after a full grace
 725 * period has elapsed, in other words after all currently executing RCU
 726 * read-side critical sections have completed.  Note, however, that
 727 * upon return from synchronize_rcu(), the caller might well be executing
 728 * concurrently with new RCU read-side critical sections that began while
 729 * synchronize_rcu() was waiting.  RCU read-side critical sections are
 730 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
 731 */
 732void synchronize_rcu(void)
 733{
 734        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 735                           !lock_is_held(&rcu_lock_map) &&
 736                           !lock_is_held(&rcu_sched_lock_map),
 737                           "Illegal synchronize_rcu() in RCU read-side critical section");
 738        if (!rcu_scheduler_active)
 739                return;
 740        wait_rcu_gp(call_rcu);
 741}
 742EXPORT_SYMBOL_GPL(synchronize_rcu);
 743
 744static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
 745static long sync_rcu_preempt_exp_count;
 746static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
 747
 748/*
 749 * Return non-zero if there are any tasks in RCU read-side critical
 750 * sections blocking the current preemptible-RCU expedited grace period.
 751 * If there is no preemptible-RCU expedited grace period currently in
 752 * progress, returns zero unconditionally.
 753 */
 754static int rcu_preempted_readers_exp(struct rcu_node *rnp)
 755{
 756        return rnp->exp_tasks != NULL;
 757}
 758
 759/*
 760 * return non-zero if there is no RCU expedited grace period in progress
 761 * for the specified rcu_node structure, in other words, if all CPUs and
 762 * tasks covered by the specified rcu_node structure have done their bit
 763 * for the current expedited grace period.  Works only for preemptible
 764 * RCU -- other RCU implementation use other means.
 765 *
 766 * Caller must hold sync_rcu_preempt_exp_mutex.
 767 */
 768static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
 769{
 770        return !rcu_preempted_readers_exp(rnp) &&
 771               ACCESS_ONCE(rnp->expmask) == 0;
 772}
 773
 774/*
 775 * Report the exit from RCU read-side critical section for the last task
 776 * that queued itself during or before the current expedited preemptible-RCU
 777 * grace period.  This event is reported either to the rcu_node structure on
 778 * which the task was queued or to one of that rcu_node structure's ancestors,
 779 * recursively up the tree.  (Calm down, calm down, we do the recursion
 780 * iteratively!)
 781 *
 782 * Most callers will set the "wake" flag, but the task initiating the
 783 * expedited grace period need not wake itself.
 784 *
 785 * Caller must hold sync_rcu_preempt_exp_mutex.
 786 */
 787static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
 788                               bool wake)
 789{
 790        unsigned long flags;
 791        unsigned long mask;
 792
 793        raw_spin_lock_irqsave(&rnp->lock, flags);
 794        for (;;) {
 795                if (!sync_rcu_preempt_exp_done(rnp)) {
 796                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 797                        break;
 798                }
 799                if (rnp->parent == NULL) {
 800                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 801                        if (wake)
 802                                wake_up(&sync_rcu_preempt_exp_wq);
 803                        break;
 804                }
 805                mask = rnp->grpmask;
 806                raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
 807                rnp = rnp->parent;
 808                raw_spin_lock(&rnp->lock); /* irqs already disabled */
 809                rnp->expmask &= ~mask;
 810        }
 811}
 812
 813/*
 814 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
 815 * grace period for the specified rcu_node structure.  If there are no such
 816 * tasks, report it up the rcu_node hierarchy.
 817 *
 818 * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
 819 */
 820static void
 821sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
 822{
 823        unsigned long flags;
 824        int must_wait = 0;
 825
 826        raw_spin_lock_irqsave(&rnp->lock, flags);
 827        if (list_empty(&rnp->blkd_tasks))
 828                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 829        else {
 830                rnp->exp_tasks = rnp->blkd_tasks.next;
 831                rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
 832                must_wait = 1;
 833        }
 834        if (!must_wait)
 835                rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
 836}
 837
 838/**
 839 * synchronize_rcu_expedited - Brute-force RCU grace period
 840 *
 841 * Wait for an RCU-preempt grace period, but expedite it.  The basic
 842 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
 843 * the ->blkd_tasks lists and wait for this list to drain.  This consumes
 844 * significant time on all CPUs and is unfriendly to real-time workloads,
 845 * so is thus not recommended for any sort of common-case code.
 846 * In fact, if you are using synchronize_rcu_expedited() in a loop,
 847 * please restructure your code to batch your updates, and then Use a
 848 * single synchronize_rcu() instead.
 849 *
 850 * Note that it is illegal to call this function while holding any lock
 851 * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
 852 * to call this function from a CPU-hotplug notifier.  Failing to observe
 853 * these restriction will result in deadlock.
 854 */
 855void synchronize_rcu_expedited(void)
 856{
 857        unsigned long flags;
 858        struct rcu_node *rnp;
 859        struct rcu_state *rsp = &rcu_preempt_state;
 860        long snap;
 861        int trycount = 0;
 862
 863        smp_mb(); /* Caller's modifications seen first by other CPUs. */
 864        snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
 865        smp_mb(); /* Above access cannot bleed into critical section. */
 866
 867        /*
 868         * Acquire lock, falling back to synchronize_rcu() if too many
 869         * lock-acquisition failures.  Of course, if someone does the
 870         * expedited grace period for us, just leave.
 871         */
 872        while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
 873                if (trycount++ < 10)
 874                        udelay(trycount * num_online_cpus());
 875                else {
 876                        synchronize_rcu();
 877                        return;
 878                }
 879                if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
 880                        goto mb_ret; /* Others did our work for us. */
 881        }
 882        if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
 883                goto unlock_mb_ret; /* Others did our work for us. */
 884
 885        /* force all RCU readers onto ->blkd_tasks lists. */
 886        synchronize_sched_expedited();
 887
 888        raw_spin_lock_irqsave(&rsp->onofflock, flags);
 889
 890        /* Initialize ->expmask for all non-leaf rcu_node structures. */
 891        rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
 892                raw_spin_lock(&rnp->lock); /* irqs already disabled. */
 893                rnp->expmask = rnp->qsmaskinit;
 894                raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
 895        }
 896
 897        /* Snapshot current state of ->blkd_tasks lists. */
 898        rcu_for_each_leaf_node(rsp, rnp)
 899                sync_rcu_preempt_exp_init(rsp, rnp);
 900        if (NUM_RCU_NODES > 1)
 901                sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
 902
 903        raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
 904
 905        /* Wait for snapshotted ->blkd_tasks lists to drain. */
 906        rnp = rcu_get_root(rsp);
 907        wait_event(sync_rcu_preempt_exp_wq,
 908                   sync_rcu_preempt_exp_done(rnp));
 909
 910        /* Clean up and exit. */
 911        smp_mb(); /* ensure expedited GP seen before counter increment. */
 912        ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
 913unlock_mb_ret:
 914        mutex_unlock(&sync_rcu_preempt_exp_mutex);
 915mb_ret:
 916        smp_mb(); /* ensure subsequent action seen after grace period. */
 917}
 918EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 919
 920/*
 921 * Check to see if there is any immediate preemptible-RCU-related work
 922 * to be done.
 923 */
 924static int rcu_preempt_pending(int cpu)
 925{
 926        return __rcu_pending(&rcu_preempt_state,
 927                             &per_cpu(rcu_preempt_data, cpu));
 928}
 929
 930/*
 931 * Does preemptible RCU have callbacks on this CPU?
 932 */
 933static int rcu_preempt_cpu_has_callbacks(int cpu)
 934{
 935        return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
 936}
 937
 938/**
 939 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 940 */
 941void rcu_barrier(void)
 942{
 943        _rcu_barrier(&rcu_preempt_state, call_rcu);
 944}
 945EXPORT_SYMBOL_GPL(rcu_barrier);
 946
 947/*
 948 * Initialize preemptible RCU's per-CPU data.
 949 */
 950static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
 951{
 952        rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
 953}
 954
 955/*
 956 * Move preemptible RCU's callbacks from dying CPU to other online CPU
 957 * and record a quiescent state.
 958 */
 959static void rcu_preempt_cleanup_dying_cpu(void)
 960{
 961        rcu_cleanup_dying_cpu(&rcu_preempt_state);
 962}
 963
 964/*
 965 * Initialize preemptible RCU's state structures.
 966 */
 967static void __init __rcu_init_preempt(void)
 968{
 969        rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
 970}
 971
 972#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 973
 974static struct rcu_state *rcu_state = &rcu_sched_state;
 975
 976/*
 977 * Tell them what RCU they are running.
 978 */
 979static void __init rcu_bootup_announce(void)
 980{
 981        printk(KERN_INFO "Hierarchical RCU implementation.\n");
 982        rcu_bootup_announce_oddness();
 983}
 984
 985/*
 986 * Return the number of RCU batches processed thus far for debug & stats.
 987 */
 988long rcu_batches_completed(void)
 989{
 990        return rcu_batches_completed_sched();
 991}
 992EXPORT_SYMBOL_GPL(rcu_batches_completed);
 993
 994/*
 995 * Force a quiescent state for RCU, which, because there is no preemptible
 996 * RCU, becomes the same as rcu-sched.
 997 */
 998void rcu_force_quiescent_state(void)
 999{
1000        rcu_sched_force_quiescent_state();
1001}
1002EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
1003
1004/*
1005 * Because preemptible RCU does not exist, we never have to check for
1006 * CPUs being in quiescent states.
1007 */
1008static void rcu_preempt_note_context_switch(int cpu)
1009{
1010}
1011
1012/*
1013 * Because preemptible RCU does not exist, there are never any preempted
1014 * RCU readers.
1015 */
1016static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
1017{
1018        return 0;
1019}
1020
1021#ifdef CONFIG_HOTPLUG_CPU
1022
1023/* Because preemptible RCU does not exist, no quieting of tasks. */
1024static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1025{
1026        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1027}
1028
1029#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1030
1031/*
1032 * Because preemptible RCU does not exist, we never have to check for
1033 * tasks blocked within RCU read-side critical sections.
1034 */
1035static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1036{
1037}
1038
1039/*
1040 * Because preemptible RCU does not exist, we never have to check for
1041 * tasks blocked within RCU read-side critical sections.
1042 */
1043static int rcu_print_task_stall(struct rcu_node *rnp)
1044{
1045        return 0;
1046}
1047
1048/*
1049 * Because preemptible RCU does not exist, there is no need to suppress
1050 * its CPU stall warnings.
1051 */
1052static void rcu_preempt_stall_reset(void)
1053{
1054}
1055
1056/*
1057 * Because there is no preemptible RCU, there can be no readers blocked,
1058 * so there is no need to check for blocked tasks.  So check only for
1059 * bogus qsmask values.
1060 */
1061static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1062{
1063        WARN_ON_ONCE(rnp->qsmask);
1064}
1065
1066#ifdef CONFIG_HOTPLUG_CPU
1067
1068/*
1069 * Because preemptible RCU does not exist, it never needs to migrate
1070 * tasks that were blocked within RCU read-side critical sections, and
1071 * such non-existent tasks cannot possibly have been blocking the current
1072 * grace period.
1073 */
1074static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1075                                     struct rcu_node *rnp,
1076                                     struct rcu_data *rdp)
1077{
1078        return 0;
1079}
1080
1081#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1082
1083/*
1084 * Because preemptible RCU does not exist, it never needs CPU-offline
1085 * processing.
1086 */
1087static void rcu_preempt_cleanup_dead_cpu(int cpu)
1088{
1089}
1090
1091/*
1092 * Because preemptible RCU does not exist, it never has any callbacks
1093 * to check.
1094 */
1095static void rcu_preempt_check_callbacks(int cpu)
1096{
1097}
1098
1099/*
1100 * Because preemptible RCU does not exist, it never has any callbacks
1101 * to process.
1102 */
1103static void rcu_preempt_process_callbacks(void)
1104{
1105}
1106
1107/*
1108 * Queue an RCU callback for lazy invocation after a grace period.
1109 * This will likely be later named something like "call_rcu_lazy()",
1110 * but this change will require some way of tagging the lazy RCU
1111 * callbacks in the list of pending callbacks.  Until then, this
1112 * function may only be called from __kfree_rcu().
1113 *
1114 * Because there is no preemptible RCU, we use RCU-sched instead.
1115 */
1116void kfree_call_rcu(struct rcu_head *head,
1117                    void (*func)(struct rcu_head *rcu))
1118{
1119        __call_rcu(head, func, &rcu_sched_state, 1);
1120}
1121EXPORT_SYMBOL_GPL(kfree_call_rcu);
1122
1123/*
1124 * Wait for an rcu-preempt grace period, but make it happen quickly.
1125 * But because preemptible RCU does not exist, map to rcu-sched.
1126 */
1127void synchronize_rcu_expedited(void)
1128{
1129        synchronize_sched_expedited();
1130}
1131EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1132
1133#ifdef CONFIG_HOTPLUG_CPU
1134
1135/*
1136 * Because preemptible RCU does not exist, there is never any need to
1137 * report on tasks preempted in RCU read-side critical sections during
1138 * expedited RCU grace periods.
1139 */
1140static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1141                               bool wake)
1142{
1143}
1144
1145#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1146
1147/*
1148 * Because preemptible RCU does not exist, it never has any work to do.
1149 */
1150static int rcu_preempt_pending(int cpu)
1151{
1152        return 0;
1153}
1154
1155/*
1156 * Because preemptible RCU does not exist, it never has callbacks
1157 */
1158static int rcu_preempt_cpu_has_callbacks(int cpu)
1159{
1160        return 0;
1161}
1162
1163/*
1164 * Because preemptible RCU does not exist, rcu_barrier() is just
1165 * another name for rcu_barrier_sched().
1166 */
1167void rcu_barrier(void)
1168{
1169        rcu_barrier_sched();
1170}
1171EXPORT_SYMBOL_GPL(rcu_barrier);
1172
1173/*
1174 * Because preemptible RCU does not exist, there is no per-CPU
1175 * data to initialize.
1176 */
1177static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
1178{
1179}
1180
1181/*
1182 * Because there is no preemptible RCU, there is no cleanup to do.
1183 */
1184static void rcu_preempt_cleanup_dying_cpu(void)
1185{
1186}
1187
1188/*
1189 * Because preemptible RCU does not exist, it need not be initialized.
1190 */
1191static void __init __rcu_init_preempt(void)
1192{
1193}
1194
1195#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1196
1197#ifdef CONFIG_RCU_BOOST
1198
1199#include "rtmutex_common.h"
1200
1201#ifdef CONFIG_RCU_TRACE
1202
1203static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1204{
1205        if (list_empty(&rnp->blkd_tasks))
1206                rnp->n_balk_blkd_tasks++;
1207        else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1208                rnp->n_balk_exp_gp_tasks++;
1209        else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1210                rnp->n_balk_boost_tasks++;
1211        else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1212                rnp->n_balk_notblocked++;
1213        else if (rnp->gp_tasks != NULL &&
1214                 ULONG_CMP_LT(jiffies, rnp->boost_time))
1215                rnp->n_balk_notyet++;
1216        else
1217                rnp->n_balk_nos++;
1218}
1219
1220#else /* #ifdef CONFIG_RCU_TRACE */
1221
1222static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1223{
1224}
1225
1226#endif /* #else #ifdef CONFIG_RCU_TRACE */
1227
1228/*
1229 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1230 * or ->boost_tasks, advancing the pointer to the next task in the
1231 * ->blkd_tasks list.
1232 *
1233 * Note that irqs must be enabled: boosting the task can block.
1234 * Returns 1 if there are more tasks needing to be boosted.
1235 */
1236static int rcu_boost(struct rcu_node *rnp)
1237{
1238        unsigned long flags;
1239        struct rt_mutex mtx;
1240        struct task_struct *t;
1241        struct list_head *tb;
1242
1243        if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1244                return 0;  /* Nothing left to boost. */
1245
1246        raw_spin_lock_irqsave(&rnp->lock, flags);
1247
1248        /*
1249         * Recheck under the lock: all tasks in need of boosting
1250         * might exit their RCU read-side critical sections on their own.
1251         */
1252        if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1253                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1254                return 0;
1255        }
1256
1257        /*
1258         * Preferentially boost tasks blocking expedited grace periods.
1259         * This cannot starve the normal grace periods because a second
1260         * expedited grace period must boost all blocked tasks, including
1261         * those blocking the pre-existing normal grace period.
1262         */
1263        if (rnp->exp_tasks != NULL) {
1264                tb = rnp->exp_tasks;
1265                rnp->n_exp_boosts++;
1266        } else {
1267                tb = rnp->boost_tasks;
1268                rnp->n_normal_boosts++;
1269        }
1270        rnp->n_tasks_boosted++;
1271
1272        /*
1273         * We boost task t by manufacturing an rt_mutex that appears to
1274         * be held by task t.  We leave a pointer to that rt_mutex where
1275         * task t can find it, and task t will release the mutex when it
1276         * exits its outermost RCU read-side critical section.  Then
1277         * simply acquiring this artificial rt_mutex will boost task
1278         * t's priority.  (Thanks to tglx for suggesting this approach!)
1279         *
1280         * Note that task t must acquire rnp->lock to remove itself from
1281         * the ->blkd_tasks list, which it will do from exit() if from
1282         * nowhere else.  We therefore are guaranteed that task t will
1283         * stay around at least until we drop rnp->lock.  Note that
1284         * rnp->lock also resolves races between our priority boosting
1285         * and task t's exiting its outermost RCU read-side critical
1286         * section.
1287         */
1288        t = container_of(tb, struct task_struct, rcu_node_entry);
1289        rt_mutex_init_proxy_locked(&mtx, t);
1290        t->rcu_boost_mutex = &mtx;
1291        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1292        rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
1293        rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
1294
1295        return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1296               ACCESS_ONCE(rnp->boost_tasks) != NULL;
1297}
1298
1299/*
1300 * Timer handler to initiate waking up of boost kthreads that
1301 * have yielded the CPU due to excessive numbers of tasks to
1302 * boost.  We wake up the per-rcu_node kthread, which in turn
1303 * will wake up the booster kthread.
1304 */
1305static void rcu_boost_kthread_timer(unsigned long arg)
1306{
1307        invoke_rcu_node_kthread((struct rcu_node *)arg);
1308}
1309
1310/*
1311 * Priority-boosting kthread.  One per leaf rcu_node and one for the
1312 * root rcu_node.
1313 */
1314static int rcu_boost_kthread(void *arg)
1315{
1316        struct rcu_node *rnp = (struct rcu_node *)arg;
1317        int spincnt = 0;
1318        int more2boost;
1319
1320        trace_rcu_utilization("Start boost kthread@init");
1321        for (;;) {
1322                rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1323                trace_rcu_utilization("End boost kthread@rcu_wait");
1324                rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1325                trace_rcu_utilization("Start boost kthread@rcu_wait");
1326                rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1327                more2boost = rcu_boost(rnp);
1328                if (more2boost)
1329                        spincnt++;
1330                else
1331                        spincnt = 0;
1332                if (spincnt > 10) {
1333                        trace_rcu_utilization("End boost kthread@rcu_yield");
1334                        rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp);
1335                        trace_rcu_utilization("Start boost kthread@rcu_yield");
1336                        spincnt = 0;
1337                }
1338        }
1339        /* NOTREACHED */
1340        trace_rcu_utilization("End boost kthread@notreached");
1341        return 0;
1342}
1343
1344/*
1345 * Check to see if it is time to start boosting RCU readers that are
1346 * blocking the current grace period, and, if so, tell the per-rcu_node
1347 * kthread to start boosting them.  If there is an expedited grace
1348 * period in progress, it is always time to boost.
1349 *
1350 * The caller must hold rnp->lock, which this function releases,
1351 * but irqs remain disabled.  The ->boost_kthread_task is immortal,
1352 * so we don't need to worry about it going away.
1353 */
1354static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1355{
1356        struct task_struct *t;
1357
1358        if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1359                rnp->n_balk_exp_gp_tasks++;
1360                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1361                return;
1362        }
1363        if (rnp->exp_tasks != NULL ||
1364            (rnp->gp_tasks != NULL &&
1365             rnp->boost_tasks == NULL &&
1366             rnp->qsmask == 0 &&
1367             ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1368                if (rnp->exp_tasks == NULL)
1369                        rnp->boost_tasks = rnp->gp_tasks;
1370                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1371                t = rnp->boost_kthread_task;
1372                if (t != NULL)
1373                        wake_up_process(t);
1374        } else {
1375                rcu_initiate_boost_trace(rnp);
1376                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1377        }
1378}
1379
1380/*
1381 * Wake up the per-CPU kthread to invoke RCU callbacks.
1382 */
1383static void invoke_rcu_callbacks_kthread(void)
1384{
1385        unsigned long flags;
1386
1387        local_irq_save(flags);
1388        __this_cpu_write(rcu_cpu_has_work, 1);
1389        if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1390            current != __this_cpu_read(rcu_cpu_kthread_task))
1391                wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
1392        local_irq_restore(flags);
1393}
1394
1395/*
1396 * Is the current CPU running the RCU-callbacks kthread?
1397 * Caller must have preemption disabled.
1398 */
1399static bool rcu_is_callbacks_kthread(void)
1400{
1401        return __get_cpu_var(rcu_cpu_kthread_task) == current;
1402}
1403
1404/*
1405 * Set the affinity of the boost kthread.  The CPU-hotplug locks are
1406 * held, so no one should be messing with the existence of the boost
1407 * kthread.
1408 */
1409static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
1410                                          cpumask_var_t cm)
1411{
1412        struct task_struct *t;
1413
1414        t = rnp->boost_kthread_task;
1415        if (t != NULL)
1416                set_cpus_allowed_ptr(rnp->boost_kthread_task, cm);
1417}
1418
1419#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1420
1421/*
1422 * Do priority-boost accounting for the start of a new grace period.
1423 */
1424static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1425{
1426        rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1427}
1428
1429/*
1430 * Create an RCU-boost kthread for the specified node if one does not
1431 * already exist.  We only create this kthread for preemptible RCU.
1432 * Returns zero if all is well, a negated errno otherwise.
1433 */
1434static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1435                                                 struct rcu_node *rnp,
1436                                                 int rnp_index)
1437{
1438        unsigned long flags;
1439        struct sched_param sp;
1440        struct task_struct *t;
1441
1442        if (&rcu_preempt_state != rsp)
1443                return 0;
1444        rsp->boost = 1;
1445        if (rnp->boost_kthread_task != NULL)
1446                return 0;
1447        t = kthread_create(rcu_boost_kthread, (void *)rnp,
1448                           "rcub/%d", rnp_index);
1449        if (IS_ERR(t))
1450                return PTR_ERR(t);
1451        raw_spin_lock_irqsave(&rnp->lock, flags);
1452        rnp->boost_kthread_task = t;
1453        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1454        sp.sched_priority = RCU_BOOST_PRIO;
1455        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1456        wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1457        return 0;
1458}
1459
1460#ifdef CONFIG_HOTPLUG_CPU
1461
1462/*
1463 * Stop the RCU's per-CPU kthread when its CPU goes offline,.
1464 */
1465static void rcu_stop_cpu_kthread(int cpu)
1466{
1467        struct task_struct *t;
1468
1469        /* Stop the CPU's kthread. */
1470        t = per_cpu(rcu_cpu_kthread_task, cpu);
1471        if (t != NULL) {
1472                per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
1473                kthread_stop(t);
1474        }
1475}
1476
1477#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1478
1479static void rcu_kthread_do_work(void)
1480{
1481        rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
1482        rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1483        rcu_preempt_do_callbacks();
1484}
1485
1486/*
1487 * Wake up the specified per-rcu_node-structure kthread.
1488 * Because the per-rcu_node kthreads are immortal, we don't need
1489 * to do anything to keep them alive.
1490 */
1491static void invoke_rcu_node_kthread(struct rcu_node *rnp)
1492{
1493        struct task_struct *t;
1494
1495        t = rnp->node_kthread_task;
1496        if (t != NULL)
1497                wake_up_process(t);
1498}
1499
1500/*
1501 * Set the specified CPU's kthread to run RT or not, as specified by
1502 * the to_rt argument.  The CPU-hotplug locks are held, so the task
1503 * is not going away.
1504 */
1505static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
1506{
1507        int policy;
1508        struct sched_param sp;
1509        struct task_struct *t;
1510
1511        t = per_cpu(rcu_cpu_kthread_task, cpu);
1512        if (t == NULL)
1513                return;
1514        if (to_rt) {
1515                policy = SCHED_FIFO;
1516                sp.sched_priority = RCU_KTHREAD_PRIO;
1517        } else {
1518                policy = SCHED_NORMAL;
1519                sp.sched_priority = 0;
1520        }
1521        sched_setscheduler_nocheck(t, policy, &sp);
1522}
1523
1524/*
1525 * Timer handler to initiate the waking up of per-CPU kthreads that
1526 * have yielded the CPU due to excess numbers of RCU callbacks.
1527 * We wake up the per-rcu_node kthread, which in turn will wake up
1528 * the booster kthread.
1529 */
1530static void rcu_cpu_kthread_timer(unsigned long arg)
1531{
1532        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
1533        struct rcu_node *rnp = rdp->mynode;
1534
1535        atomic_or(rdp->grpmask, &rnp->wakemask);
1536        invoke_rcu_node_kthread(rnp);
1537}
1538
1539/*
1540 * Drop to non-real-time priority and yield, but only after posting a
1541 * timer that will cause us to regain our real-time priority if we
1542 * remain preempted.  Either way, we restore our real-time priority
1543 * before returning.
1544 */
1545static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
1546{
1547        struct sched_param sp;
1548        struct timer_list yield_timer;
1549        int prio = current->rt_priority;
1550
1551        setup_timer_on_stack(&yield_timer, f, arg);
1552        mod_timer(&yield_timer, jiffies + 2);
1553        sp.sched_priority = 0;
1554        sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
1555        set_user_nice(current, 19);
1556        schedule();
1557        set_user_nice(current, 0);
1558        sp.sched_priority = prio;
1559        sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1560        del_timer(&yield_timer);
1561}
1562
1563/*
1564 * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
1565 * This can happen while the corresponding CPU is either coming online
1566 * or going offline.  We cannot wait until the CPU is fully online
1567 * before starting the kthread, because the various notifier functions
1568 * can wait for RCU grace periods.  So we park rcu_cpu_kthread() until
1569 * the corresponding CPU is online.
1570 *
1571 * Return 1 if the kthread needs to stop, 0 otherwise.
1572 *
1573 * Caller must disable bh.  This function can momentarily enable it.
1574 */
1575static int rcu_cpu_kthread_should_stop(int cpu)
1576{
1577        while (cpu_is_offline(cpu) ||
1578               !cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)) ||
1579               smp_processor_id() != cpu) {
1580                if (kthread_should_stop())
1581                        return 1;
1582                per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1583                per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
1584                local_bh_enable();
1585                schedule_timeout_uninterruptible(1);
1586                if (!cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)))
1587                        set_cpus_allowed_ptr(current, cpumask_of(cpu));
1588                local_bh_disable();
1589        }
1590        per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
1591        return 0;
1592}
1593
1594/*
1595 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1596 * RCU softirq used in flavors and configurations of RCU that do not
1597 * support RCU priority boosting.
1598 */
1599static int rcu_cpu_kthread(void *arg)
1600{
1601        int cpu = (int)(long)arg;
1602        unsigned long flags;
1603        int spincnt = 0;
1604        unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
1605        char work;
1606        char *workp = &per_cpu(rcu_cpu_has_work, cpu);
1607
1608        trace_rcu_utilization("Start CPU kthread@init");
1609        for (;;) {
1610                *statusp = RCU_KTHREAD_WAITING;
1611                trace_rcu_utilization("End CPU kthread@rcu_wait");
1612                rcu_wait(*workp != 0 || kthread_should_stop());
1613                trace_rcu_utilization("Start CPU kthread@rcu_wait");
1614                local_bh_disable();
1615                if (rcu_cpu_kthread_should_stop(cpu)) {
1616                        local_bh_enable();
1617                        break;
1618                }
1619                *statusp = RCU_KTHREAD_RUNNING;
1620                per_cpu(rcu_cpu_kthread_loops, cpu)++;
1621                local_irq_save(flags);
1622                work = *workp;
1623                *workp = 0;
1624                local_irq_restore(flags);
1625                if (work)
1626                        rcu_kthread_do_work();
1627                local_bh_enable();
1628                if (*workp != 0)
1629                        spincnt++;
1630                else
1631                        spincnt = 0;
1632                if (spincnt > 10) {
1633                        *statusp = RCU_KTHREAD_YIELDING;
1634                        trace_rcu_utilization("End CPU kthread@rcu_yield");
1635                        rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
1636                        trace_rcu_utilization("Start CPU kthread@rcu_yield");
1637                        spincnt = 0;
1638                }
1639        }
1640        *statusp = RCU_KTHREAD_STOPPED;
1641        trace_rcu_utilization("End CPU kthread@term");
1642        return 0;
1643}
1644
1645/*
1646 * Spawn a per-CPU kthread, setting up affinity and priority.
1647 * Because the CPU hotplug lock is held, no other CPU will be attempting
1648 * to manipulate rcu_cpu_kthread_task.  There might be another CPU
1649 * attempting to access it during boot, but the locking in kthread_bind()
1650 * will enforce sufficient ordering.
1651 *
1652 * Please note that we cannot simply refuse to wake up the per-CPU
1653 * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
1654 * which can result in softlockup complaints if the task ends up being
1655 * idle for more than a couple of minutes.
1656 *
1657 * However, please note also that we cannot bind the per-CPU kthread to its
1658 * CPU until that CPU is fully online.  We also cannot wait until the
1659 * CPU is fully online before we create its per-CPU kthread, as this would
1660 * deadlock the system when CPU notifiers tried waiting for grace
1661 * periods.  So we bind the per-CPU kthread to its CPU only if the CPU
1662 * is online.  If its CPU is not yet fully online, then the code in
1663 * rcu_cpu_kthread() will wait until it is fully online, and then do
1664 * the binding.
1665 */
1666static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
1667{
1668        struct sched_param sp;
1669        struct task_struct *t;
1670
1671        if (!rcu_scheduler_fully_active ||
1672            per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
1673                return 0;
1674        t = kthread_create_on_node(rcu_cpu_kthread,
1675                                   (void *)(long)cpu,
1676                                   cpu_to_node(cpu),
1677                                   "rcuc/%d", cpu);
1678        if (IS_ERR(t))
1679                return PTR_ERR(t);
1680        if (cpu_online(cpu))
1681                kthread_bind(t, cpu);
1682        per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
1683        WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
1684        sp.sched_priority = RCU_KTHREAD_PRIO;
1685        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1686        per_cpu(rcu_cpu_kthread_task, cpu) = t;
1687        wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
1688        return 0;
1689}
1690
1691/*
1692 * Per-rcu_node kthread, which is in charge of waking up the per-CPU
1693 * kthreads when needed.  We ignore requests to wake up kthreads
1694 * for offline CPUs, which is OK because force_quiescent_state()
1695 * takes care of this case.
1696 */
1697static int rcu_node_kthread(void *arg)
1698{
1699        int cpu;
1700        unsigned long flags;
1701        unsigned long mask;
1702        struct rcu_node *rnp = (struct rcu_node *)arg;
1703        struct sched_param sp;
1704        struct task_struct *t;
1705
1706        for (;;) {
1707                rnp->node_kthread_status = RCU_KTHREAD_WAITING;
1708                rcu_wait(atomic_read(&rnp->wakemask) != 0);
1709                rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
1710                raw_spin_lock_irqsave(&rnp->lock, flags);
1711                mask = atomic_xchg(&rnp->wakemask, 0);
1712                rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
1713                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
1714                        if ((mask & 0x1) == 0)
1715                                continue;
1716                        preempt_disable();
1717                        t = per_cpu(rcu_cpu_kthread_task, cpu);
1718                        if (!cpu_online(cpu) || t == NULL) {
1719                                preempt_enable();
1720                                continue;
1721                        }
1722                        per_cpu(rcu_cpu_has_work, cpu) = 1;
1723                        sp.sched_priority = RCU_KTHREAD_PRIO;
1724                        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1725                        preempt_enable();
1726                }
1727        }
1728        /* NOTREACHED */
1729        rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
1730        return 0;
1731}
1732
1733/*
1734 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1735 * served by the rcu_node in question.  The CPU hotplug lock is still
1736 * held, so the value of rnp->qsmaskinit will be stable.
1737 *
1738 * We don't include outgoingcpu in the affinity set, use -1 if there is
1739 * no outgoing CPU.  If there are no CPUs left in the affinity set,
1740 * this function allows the kthread to execute on any CPU.
1741 */
1742static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1743{
1744        cpumask_var_t cm;
1745        int cpu;
1746        unsigned long mask = rnp->qsmaskinit;
1747
1748        if (rnp->node_kthread_task == NULL)
1749                return;
1750        if (!alloc_cpumask_var(&cm, GFP_KERNEL))
1751                return;
1752        cpumask_clear(cm);
1753        for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1754                if ((mask & 0x1) && cpu != outgoingcpu)
1755                        cpumask_set_cpu(cpu, cm);
1756        if (cpumask_weight(cm) == 0) {
1757                cpumask_setall(cm);
1758                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1759                        cpumask_clear_cpu(cpu, cm);
1760                WARN_ON_ONCE(cpumask_weight(cm) == 0);
1761        }
1762        set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
1763        rcu_boost_kthread_setaffinity(rnp, cm);
1764        free_cpumask_var(cm);
1765}
1766
1767/*
1768 * Spawn a per-rcu_node kthread, setting priority and affinity.
1769 * Called during boot before online/offline can happen, or, if
1770 * during runtime, with the main CPU-hotplug locks held.  So only
1771 * one of these can be executing at a time.
1772 */
1773static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
1774                                                struct rcu_node *rnp)
1775{
1776        unsigned long flags;
1777        int rnp_index = rnp - &rsp->node[0];
1778        struct sched_param sp;
1779        struct task_struct *t;
1780
1781        if (!rcu_scheduler_fully_active ||
1782            rnp->qsmaskinit == 0)
1783                return 0;
1784        if (rnp->node_kthread_task == NULL) {
1785                t = kthread_create(rcu_node_kthread, (void *)rnp,
1786                                   "rcun/%d", rnp_index);
1787                if (IS_ERR(t))
1788                        return PTR_ERR(t);
1789                raw_spin_lock_irqsave(&rnp->lock, flags);
1790                rnp->node_kthread_task = t;
1791                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1792                sp.sched_priority = 99;
1793                sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1794                wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1795        }
1796        return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
1797}
1798
1799/*
1800 * Spawn all kthreads -- called as soon as the scheduler is running.
1801 */
1802static int __init rcu_spawn_kthreads(void)
1803{
1804        int cpu;
1805        struct rcu_node *rnp;
1806
1807        rcu_scheduler_fully_active = 1;
1808        for_each_possible_cpu(cpu) {
1809                per_cpu(rcu_cpu_has_work, cpu) = 0;
1810                if (cpu_online(cpu))
1811                        (void)rcu_spawn_one_cpu_kthread(cpu);
1812        }
1813        rnp = rcu_get_root(rcu_state);
1814        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
1815        if (NUM_RCU_NODES > 1) {
1816                rcu_for_each_leaf_node(rcu_state, rnp)
1817                        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
1818        }
1819        return 0;
1820}
1821early_initcall(rcu_spawn_kthreads);
1822
1823static void __cpuinit rcu_prepare_kthreads(int cpu)
1824{
1825        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1826        struct rcu_node *rnp = rdp->mynode;
1827
1828        /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1829        if (rcu_scheduler_fully_active) {
1830                (void)rcu_spawn_one_cpu_kthread(cpu);
1831                if (rnp->node_kthread_task == NULL)
1832                        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
1833        }
1834}
1835
1836#else /* #ifdef CONFIG_RCU_BOOST */
1837
1838static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1839{
1840        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1841}
1842
1843static void invoke_rcu_callbacks_kthread(void)
1844{
1845        WARN_ON_ONCE(1);
1846}
1847
1848static bool rcu_is_callbacks_kthread(void)
1849{
1850        return false;
1851}
1852
1853static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1854{
1855}
1856
1857#ifdef CONFIG_HOTPLUG_CPU
1858
1859static void rcu_stop_cpu_kthread(int cpu)
1860{
1861}
1862
1863#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1864
1865static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1866{
1867}
1868
1869static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
1870{
1871}
1872
1873static int __init rcu_scheduler_really_started(void)
1874{
1875        rcu_scheduler_fully_active = 1;
1876        return 0;
1877}
1878early_initcall(rcu_scheduler_really_started);
1879
1880static void __cpuinit rcu_prepare_kthreads(int cpu)
1881{
1882}
1883
1884#endif /* #else #ifdef CONFIG_RCU_BOOST */
1885
1886#if !defined(CONFIG_RCU_FAST_NO_HZ)
1887
1888/*
1889 * Check to see if any future RCU-related work will need to be done
1890 * by the current CPU, even if none need be done immediately, returning
1891 * 1 if so.  This function is part of the RCU implementation; it is -not-
1892 * an exported member of the RCU API.
1893 *
1894 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1895 * any flavor of RCU.
1896 */
1897int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1898{
1899        *delta_jiffies = ULONG_MAX;
1900        return rcu_cpu_has_callbacks(cpu);
1901}
1902
1903/*
1904 * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
1905 */
1906static void rcu_prepare_for_idle_init(int cpu)
1907{
1908}
1909
1910/*
1911 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1912 * after it.
1913 */
1914static void rcu_cleanup_after_idle(int cpu)
1915{
1916}
1917
1918/*
1919 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1920 * is nothing.
1921 */
1922static void rcu_prepare_for_idle(int cpu)
1923{
1924}
1925
1926/*
1927 * Don't bother keeping a running count of the number of RCU callbacks
1928 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1929 */
1930static void rcu_idle_count_callbacks_posted(void)
1931{
1932}
1933
1934#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1935
1936/*
1937 * This code is invoked when a CPU goes idle, at which point we want
1938 * to have the CPU do everything required for RCU so that it can enter
1939 * the energy-efficient dyntick-idle mode.  This is handled by a
1940 * state machine implemented by rcu_prepare_for_idle() below.
1941 *
1942 * The following three proprocessor symbols control this state machine:
1943 *
1944 * RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt
1945 *      to satisfy RCU.  Beyond this point, it is better to incur a periodic
1946 *      scheduling-clock interrupt than to loop through the state machine
1947 *      at full power.
1948 * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are
1949 *      optional if RCU does not need anything immediately from this
1950 *      CPU, even if this CPU still has RCU callbacks queued.  The first
1951 *      times through the state machine are mandatory: we need to give
1952 *      the state machine a chance to communicate a quiescent state
1953 *      to the RCU core.
1954 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1955 *      to sleep in dyntick-idle mode with RCU callbacks pending.  This
1956 *      is sized to be roughly one RCU grace period.  Those energy-efficiency
1957 *      benchmarkers who might otherwise be tempted to set this to a large
1958 *      number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1959 *      system.  And if you are -that- concerned about energy efficiency,
1960 *      just power the system down and be done with it!
1961 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1962 *      permitted to sleep in dyntick-idle mode with only lazy RCU
1963 *      callbacks pending.  Setting this too high can OOM your system.
1964 *
1965 * The values below work well in practice.  If future workloads require
1966 * adjustment, they can be converted into kernel config parameters, though
1967 * making the state machine smarter might be a better option.
1968 */
1969#define RCU_IDLE_FLUSHES 5              /* Number of dyntick-idle tries. */
1970#define RCU_IDLE_OPT_FLUSHES 3          /* Optional dyntick-idle tries. */
1971#define RCU_IDLE_GP_DELAY 6             /* Roughly one grace period. */
1972#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1973
1974/*
1975 * Does the specified flavor of RCU have non-lazy callbacks pending on
1976 * the specified CPU?  Both RCU flavor and CPU are specified by the
1977 * rcu_data structure.
1978 */
1979static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
1980{
1981        return rdp->qlen != rdp->qlen_lazy;
1982}
1983
1984#ifdef CONFIG_TREE_PREEMPT_RCU
1985
1986/*
1987 * Are there non-lazy RCU-preempt callbacks?  (There cannot be if there
1988 * is no RCU-preempt in the kernel.)
1989 */
1990static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
1991{
1992        struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
1993
1994        return __rcu_cpu_has_nonlazy_callbacks(rdp);
1995}
1996
1997#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
1998
1999static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
2000{
2001        return 0;
2002}
2003
2004#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
2005
2006/*
2007 * Does any flavor of RCU have non-lazy callbacks on the specified CPU?
2008 */
2009static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
2010{
2011        return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
2012               __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
2013               rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
2014}
2015
2016/*
2017 * Allow the CPU to enter dyntick-idle mode if either: (1) There are no
2018 * callbacks on this CPU, (2) this CPU has not yet attempted to enter
2019 * dyntick-idle mode, or (3) this CPU is in the process of attempting to
2020 * enter dyntick-idle mode.  Otherwise, if we have recently tried and failed
2021 * to enter dyntick-idle mode, we refuse to try to enter it.  After all,
2022 * it is better to incur scheduling-clock interrupts than to spin
2023 * continuously for the same time duration!
2024 *
2025 * The delta_jiffies argument is used to store the time when RCU is
2026 * going to need the CPU again if it still has callbacks.  The reason
2027 * for this is that rcu_prepare_for_idle() might need to post a timer,
2028 * but if so, it will do so after tick_nohz_stop_sched_tick() has set
2029 * the wakeup time for this CPU.  This means that RCU's timer can be
2030 * delayed until the wakeup time, which defeats the purpose of posting
2031 * a timer.
2032 */
2033int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
2034{
2035        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
2036
2037        /* Flag a new idle sojourn to the idle-entry state machine. */
2038        rdtp->idle_first_pass = 1;
2039        /* If no callbacks, RCU doesn't need the CPU. */
2040        if (!rcu_cpu_has_callbacks(cpu)) {
2041                *delta_jiffies = ULONG_MAX;
2042                return 0;
2043        }
2044        if (rdtp->dyntick_holdoff == jiffies) {
2045                /* RCU recently tried and failed, so don't try again. */
2046                *delta_jiffies = 1;
2047                return 1;
2048        }
2049        /* Set up for the possibility that RCU will post a timer. */
2050        if (rcu_cpu_has_nonlazy_callbacks(cpu))
2051                *delta_jiffies = RCU_IDLE_GP_DELAY;
2052        else
2053                *delta_jiffies = RCU_IDLE_LAZY_GP_DELAY;
2054        return 0;
2055}
2056
2057/*
2058 * Handler for smp_call_function_single().  The only point of this
2059 * handler is to wake the CPU up, so the handler does only tracing.
2060 */
2061void rcu_idle_demigrate(void *unused)
2062{
2063        trace_rcu_prep_idle("Demigrate");
2064}
2065
2066/*
2067 * Timer handler used to force CPU to start pushing its remaining RCU
2068 * callbacks in the case where it entered dyntick-idle mode with callbacks
2069 * pending.  The hander doesn't really need to do anything because the
2070 * real work is done upon re-entry to idle, or by the next scheduling-clock
2071 * interrupt should idle not be re-entered.
2072 *
2073 * One special case: the timer gets migrated without awakening the CPU
2074 * on which the timer was scheduled on.  In this case, we must wake up
2075 * that CPU.  We do so with smp_call_function_single().
2076 */
2077static void rcu_idle_gp_timer_func(unsigned long cpu_in)
2078{
2079        int cpu = (int)cpu_in;
2080
2081        trace_rcu_prep_idle("Timer");
2082        if (cpu != smp_processor_id())
2083                smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0);
2084        else
2085                WARN_ON_ONCE(1); /* Getting here can hang the system... */
2086}
2087
2088/*
2089 * Initialize the timer used to pull CPUs out of dyntick-idle mode.
2090 */
2091static void rcu_prepare_for_idle_init(int cpu)
2092{
2093        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
2094
2095        rdtp->dyntick_holdoff = jiffies - 1;
2096        setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu);
2097        rdtp->idle_gp_timer_expires = jiffies - 1;
2098        rdtp->idle_first_pass = 1;
2099}
2100
2101/*
2102 * Clean up for exit from idle.  Because we are exiting from idle, there
2103 * is no longer any point to ->idle_gp_timer, so cancel it.  This will
2104 * do nothing if this timer is not active, so just cancel it unconditionally.
2105 */
2106static void rcu_cleanup_after_idle(int cpu)
2107{
2108        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
2109
2110        del_timer(&rdtp->idle_gp_timer);
2111        trace_rcu_prep_idle("Cleanup after idle");
2112}
2113
2114/*
2115 * Check to see if any RCU-related work can be done by the current CPU,
2116 * and if so, schedule a softirq to get it done.  This function is part
2117 * of the RCU implementation; it is -not- an exported member of the RCU API.
2118 *
2119 * The idea is for the current CPU to clear out all work required by the
2120 * RCU core for the current grace period, so that this CPU can be permitted
2121 * to enter dyntick-idle mode.  In some cases, it will need to be awakened
2122 * at the end of the grace period by whatever CPU ends the grace period.
2123 * This allows CPUs to go dyntick-idle more quickly, and to reduce the
2124 * number of wakeups by a modest integer factor.
2125 *
2126 * Because it is not legal to invoke rcu_process_callbacks() with irqs
2127 * disabled, we do one pass of force_quiescent_state(), then do a
2128 * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
2129 * later.  The ->dyntick_drain field controls the sequencing.
2130 *
2131 * The caller must have disabled interrupts.
2132 */
2133static void rcu_prepare_for_idle(int cpu)
2134{
2135        struct timer_list *tp;
2136        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
2137
2138        /*
2139         * If this is an idle re-entry, for example, due to use of
2140         * RCU_NONIDLE() or the new idle-loop tracing API within the idle
2141         * loop, then don't take any state-machine actions, unless the
2142         * momentary exit from idle queued additional non-lazy callbacks.
2143         * Instead, repost the ->idle_gp_timer if this CPU has callbacks
2144         * pending.
2145         */
2146        if (!rdtp->idle_first_pass &&
2147            (rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) {
2148                if (rcu_cpu_has_callbacks(cpu)) {
2149                        tp = &rdtp->idle_gp_timer;
2150                        mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
2151                }
2152                return;
2153        }
2154        rdtp->idle_first_pass = 0;
2155        rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1;
2156
2157        /*
2158         * If there are no callbacks on this CPU, enter dyntick-idle mode.
2159         * Also reset state to avoid prejudicing later attempts.
2160         */
2161        if (!rcu_cpu_has_callbacks(cpu)) {
2162                rdtp->dyntick_holdoff = jiffies - 1;
2163                rdtp->dyntick_drain = 0;
2164                trace_rcu_prep_idle("No callbacks");
2165                return;
2166        }
2167
2168        /*
2169         * If in holdoff mode, just return.  We will presumably have
2170         * refrained from disabling the scheduling-clock tick.
2171         */
2172        if (rdtp->dyntick_holdoff == jiffies) {
2173                trace_rcu_prep_idle("In holdoff");
2174                return;
2175        }
2176
2177        /* Check and update the ->dyntick_drain sequencing. */
2178        if (rdtp->dyntick_drain <= 0) {
2179                /* First time through, initialize the counter. */
2180                rdtp->dyntick_drain = RCU_IDLE_FLUSHES;
2181        } else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&
2182                   !rcu_pending(cpu) &&
2183                   !local_softirq_pending()) {
2184                /* Can we go dyntick-idle despite still having callbacks? */
2185                rdtp->dyntick_drain = 0;
2186                rdtp->dyntick_holdoff = jiffies;
2187                if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
2188                        trace_rcu_prep_idle("Dyntick with callbacks");
2189                        rdtp->idle_gp_timer_expires =
2190                                           jiffies + RCU_IDLE_GP_DELAY;
2191                } else {
2192                        rdtp->idle_gp_timer_expires =
2193                                           jiffies + RCU_IDLE_LAZY_GP_DELAY;
2194                        trace_rcu_prep_idle("Dyntick with lazy callbacks");
2195                }
2196                tp = &rdtp->idle_gp_timer;
2197                mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
2198                rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
2199                return; /* Nothing more to do immediately. */
2200        } else if (--(rdtp->dyntick_drain) <= 0) {
2201                /* We have hit the limit, so time to give up. */
2202                rdtp->dyntick_holdoff = jiffies;
2203                trace_rcu_prep_idle("Begin holdoff");
2204                invoke_rcu_core();  /* Force the CPU out of dyntick-idle. */
2205                return;
2206        }
2207
2208        /*
2209         * Do one step of pushing the remaining RCU callbacks through
2210         * the RCU core state machine.
2211         */
2212#ifdef CONFIG_TREE_PREEMPT_RCU
2213        if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
2214                rcu_preempt_qs(cpu);
2215                force_quiescent_state(&rcu_preempt_state, 0);
2216        }
2217#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
2218        if (per_cpu(rcu_sched_data, cpu).nxtlist) {
2219                rcu_sched_qs(cpu);
2220                force_quiescent_state(&rcu_sched_state, 0);
2221        }
2222        if (per_cpu(rcu_bh_data, cpu).nxtlist) {
2223                rcu_bh_qs(cpu);
2224                force_quiescent_state(&rcu_bh_state, 0);
2225        }
2226
2227        /*
2228         * If RCU callbacks are still pending, RCU still needs this CPU.
2229         * So try forcing the callbacks through the grace period.
2230         */
2231        if (rcu_cpu_has_callbacks(cpu)) {
2232                trace_rcu_prep_idle("More callbacks");
2233                invoke_rcu_core();
2234        } else
2235                trace_rcu_prep_idle("Callbacks drained");
2236}
2237
2238/*
2239 * Keep a running count of the number of non-lazy callbacks posted
2240 * on this CPU.  This running counter (which is never decremented) allows
2241 * rcu_prepare_for_idle() to detect when something out of the idle loop
2242 * posts a callback, even if an equal number of callbacks are invoked.
2243 * Of course, callbacks should only be posted from within a trace event
2244 * designed to be called from idle or from within RCU_NONIDLE().
2245 */
2246static void rcu_idle_count_callbacks_posted(void)
2247{
2248        __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
2249}
2250
2251#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
2252
2253#ifdef CONFIG_RCU_CPU_STALL_INFO
2254
2255#ifdef CONFIG_RCU_FAST_NO_HZ
2256
2257static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
2258{
2259        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
2260        struct timer_list *tltp = &rdtp->idle_gp_timer;
2261
2262        sprintf(cp, "drain=%d %c timer=%lu",
2263                rdtp->dyntick_drain,
2264                rdtp->dyntick_holdoff == jiffies ? 'H' : '.',
2265                timer_pending(tltp) ? tltp->expires - jiffies : -1);
2266}
2267
2268#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
2269
2270static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
2271{
2272}
2273
2274#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
2275
2276/* Initiate the stall-info list. */
2277static void print_cpu_stall_info_begin(void)
2278{
2279        printk(KERN_CONT "\n");
2280}
2281
2282/*
2283 * Print out diagnostic information for the specified stalled CPU.
2284 *
2285 * If the specified CPU is aware of the current RCU grace period
2286 * (flavor specified by rsp), then print the number of scheduling
2287 * clock interrupts the CPU has taken during the time that it has
2288 * been aware.  Otherwise, print the number of RCU grace periods
2289 * that this CPU is ignorant of, for example, "1" if the CPU was
2290 * aware of the previous grace period.
2291 *
2292 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
2293 */
2294static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
2295{
2296        char fast_no_hz[72];
2297        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2298        struct rcu_dynticks *rdtp = rdp->dynticks;
2299        char *ticks_title;
2300        unsigned long ticks_value;
2301
2302        if (rsp->gpnum == rdp->gpnum) {
2303                ticks_title = "ticks this GP";
2304                ticks_value = rdp->ticks_this_gp;
2305        } else {
2306                ticks_title = "GPs behind";
2307                ticks_value = rsp->gpnum - rdp->gpnum;
2308        }
2309        print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
2310        printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
2311               cpu, ticks_value, ticks_title,
2312               atomic_read(&rdtp->dynticks) & 0xfff,
2313               rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
2314               fast_no_hz);
2315}
2316
2317/* Terminate the stall-info list. */
2318static void print_cpu_stall_info_end(void)
2319{
2320        printk(KERN_ERR "\t");
2321}
2322
2323/* Zero ->ticks_this_gp for all flavors of RCU. */
2324static void zero_cpu_stall_ticks(struct rcu_data *rdp)
2325{
2326        rdp->ticks_this_gp = 0;
2327}
2328
2329/* Increment ->ticks_this_gp for all flavors of RCU. */
2330static void increment_cpu_stall_ticks(void)
2331{
2332        __get_cpu_var(rcu_sched_data).ticks_this_gp++;
2333        __get_cpu_var(rcu_bh_data).ticks_this_gp++;
2334#ifdef CONFIG_TREE_PREEMPT_RCU
2335        __get_cpu_var(rcu_preempt_data).ticks_this_gp++;
2336#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
2337}
2338
2339#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
2340
2341static void print_cpu_stall_info_begin(void)
2342{
2343        printk(KERN_CONT " {");
2344}
2345
2346static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
2347{
2348        printk(KERN_CONT " %d", cpu);
2349}
2350
2351static void print_cpu_stall_info_end(void)
2352{
2353        printk(KERN_CONT "} ");
2354}
2355
2356static void zero_cpu_stall_ticks(struct rcu_data *rdp)
2357{
2358}
2359
2360static void increment_cpu_stall_ticks(void)
2361{
2362}
2363
2364#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
2365
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.