linux/kernel/rcutree_plugin.h
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   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#include <linux/gfp.h>
  29#include <linux/oom.h>
  30#include <linux/smpboot.h>
  31#include <linux/tick.h>
  32
  33#define RCU_KTHREAD_PRIO 1
  34
  35#ifdef CONFIG_RCU_BOOST
  36#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
  37#else
  38#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
  39#endif
  40
  41#ifdef CONFIG_RCU_NOCB_CPU
  42static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
  43static bool have_rcu_nocb_mask;     /* Was rcu_nocb_mask allocated? */
  44static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */
  45static char __initdata nocb_buf[NR_CPUS * 5];
  46#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
  47
  48/*
  49 * Check the RCU kernel configuration parameters and print informative
  50 * messages about anything out of the ordinary.  If you like #ifdef, you
  51 * will love this function.
  52 */
  53static void __init rcu_bootup_announce_oddness(void)
  54{
  55#ifdef CONFIG_RCU_TRACE
  56        printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
  57#endif
  58#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
  59        printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
  60               CONFIG_RCU_FANOUT);
  61#endif
  62#ifdef CONFIG_RCU_FANOUT_EXACT
  63        printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
  64#endif
  65#ifdef CONFIG_RCU_FAST_NO_HZ
  66        printk(KERN_INFO
  67               "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
  68#endif
  69#ifdef CONFIG_PROVE_RCU
  70        printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
  71#endif
  72#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
  73        printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
  74#endif
  75#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
  76        printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
  77#endif
  78#if defined(CONFIG_RCU_CPU_STALL_INFO)
  79        printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
  80#endif
  81#if NUM_RCU_LVL_4 != 0
  82        printk(KERN_INFO "\tFour-level hierarchy is enabled.\n");
  83#endif
  84        if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
  85                printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
  86        if (nr_cpu_ids != NR_CPUS)
  87                printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
  88#ifdef CONFIG_RCU_NOCB_CPU
  89#ifndef CONFIG_RCU_NOCB_CPU_NONE
  90        if (!have_rcu_nocb_mask) {
  91                zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
  92                have_rcu_nocb_mask = true;
  93        }
  94#ifdef CONFIG_RCU_NOCB_CPU_ZERO
  95        pr_info("\tExperimental no-CBs CPU 0\n");
  96        cpumask_set_cpu(0, rcu_nocb_mask);
  97#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
  98#ifdef CONFIG_RCU_NOCB_CPU_ALL
  99        pr_info("\tExperimental no-CBs for all CPUs\n");
 100        cpumask_setall(rcu_nocb_mask);
 101#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
 102#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
 103        if (have_rcu_nocb_mask) {
 104                cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
 105                pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf);
 106                if (rcu_nocb_poll)
 107                        pr_info("\tExperimental polled no-CBs CPUs.\n");
 108        }
 109#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
 110}
 111
 112#ifdef CONFIG_TREE_PREEMPT_RCU
 113
 114struct rcu_state rcu_preempt_state =
 115        RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
 116DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
 117static struct rcu_state *rcu_state = &rcu_preempt_state;
 118
 119static int rcu_preempted_readers_exp(struct rcu_node *rnp);
 120
 121/*
 122 * Tell them what RCU they are running.
 123 */
 124static void __init rcu_bootup_announce(void)
 125{
 126        printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
 127        rcu_bootup_announce_oddness();
 128}
 129
 130/*
 131 * Return the number of RCU-preempt batches processed thus far
 132 * for debug and statistics.
 133 */
 134long rcu_batches_completed_preempt(void)
 135{
 136        return rcu_preempt_state.completed;
 137}
 138EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
 139
 140/*
 141 * Return the number of RCU batches processed thus far for debug & stats.
 142 */
 143long rcu_batches_completed(void)
 144{
 145        return rcu_batches_completed_preempt();
 146}
 147EXPORT_SYMBOL_GPL(rcu_batches_completed);
 148
 149/*
 150 * Force a quiescent state for preemptible RCU.
 151 */
 152void rcu_force_quiescent_state(void)
 153{
 154        force_quiescent_state(&rcu_preempt_state);
 155}
 156EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
 157
 158/*
 159 * Record a preemptible-RCU quiescent state for the specified CPU.  Note
 160 * that this just means that the task currently running on the CPU is
 161 * not in a quiescent state.  There might be any number of tasks blocked
 162 * while in an RCU read-side critical section.
 163 *
 164 * Unlike the other rcu_*_qs() functions, callers to this function
 165 * must disable irqs in order to protect the assignment to
 166 * ->rcu_read_unlock_special.
 167 */
 168static void rcu_preempt_qs(int cpu)
 169{
 170        struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
 171
 172        if (rdp->passed_quiesce == 0)
 173                trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
 174        rdp->passed_quiesce = 1;
 175        current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
 176}
 177
 178/*
 179 * We have entered the scheduler, and the current task might soon be
 180 * context-switched away from.  If this task is in an RCU read-side
 181 * critical section, we will no longer be able to rely on the CPU to
 182 * record that fact, so we enqueue the task on the blkd_tasks list.
 183 * The task will dequeue itself when it exits the outermost enclosing
 184 * RCU read-side critical section.  Therefore, the current grace period
 185 * cannot be permitted to complete until the blkd_tasks list entries
 186 * predating the current grace period drain, in other words, until
 187 * rnp->gp_tasks becomes NULL.
 188 *
 189 * Caller must disable preemption.
 190 */
 191static void rcu_preempt_note_context_switch(int cpu)
 192{
 193        struct task_struct *t = current;
 194        unsigned long flags;
 195        struct rcu_data *rdp;
 196        struct rcu_node *rnp;
 197
 198        if (t->rcu_read_lock_nesting > 0 &&
 199            (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 200
 201                /* Possibly blocking in an RCU read-side critical section. */
 202                rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
 203                rnp = rdp->mynode;
 204                raw_spin_lock_irqsave(&rnp->lock, flags);
 205                t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
 206                t->rcu_blocked_node = rnp;
 207
 208                /*
 209                 * If this CPU has already checked in, then this task
 210                 * will hold up the next grace period rather than the
 211                 * current grace period.  Queue the task accordingly.
 212                 * If the task is queued for the current grace period
 213                 * (i.e., this CPU has not yet passed through a quiescent
 214                 * state for the current grace period), then as long
 215                 * as that task remains queued, the current grace period
 216                 * cannot end.  Note that there is some uncertainty as
 217                 * to exactly when the current grace period started.
 218                 * We take a conservative approach, which can result
 219                 * in unnecessarily waiting on tasks that started very
 220                 * slightly after the current grace period began.  C'est
 221                 * la vie!!!
 222                 *
 223                 * But first, note that the current CPU must still be
 224                 * on line!
 225                 */
 226                WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
 227                WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
 228                if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
 229                        list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
 230                        rnp->gp_tasks = &t->rcu_node_entry;
 231#ifdef CONFIG_RCU_BOOST
 232                        if (rnp->boost_tasks != NULL)
 233                                rnp->boost_tasks = rnp->gp_tasks;
 234#endif /* #ifdef CONFIG_RCU_BOOST */
 235                } else {
 236                        list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
 237                        if (rnp->qsmask & rdp->grpmask)
 238                                rnp->gp_tasks = &t->rcu_node_entry;
 239                }
 240                trace_rcu_preempt_task(rdp->rsp->name,
 241                                       t->pid,
 242                                       (rnp->qsmask & rdp->grpmask)
 243                                       ? rnp->gpnum
 244                                       : rnp->gpnum + 1);
 245                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 246        } else if (t->rcu_read_lock_nesting < 0 &&
 247                   t->rcu_read_unlock_special) {
 248
 249                /*
 250                 * Complete exit from RCU read-side critical section on
 251                 * behalf of preempted instance of __rcu_read_unlock().
 252                 */
 253                rcu_read_unlock_special(t);
 254        }
 255
 256        /*
 257         * Either we were not in an RCU read-side critical section to
 258         * begin with, or we have now recorded that critical section
 259         * globally.  Either way, we can now note a quiescent state
 260         * for this CPU.  Again, if we were in an RCU read-side critical
 261         * section, and if that critical section was blocking the current
 262         * grace period, then the fact that the task has been enqueued
 263         * means that we continue to block the current grace period.
 264         */
 265        local_irq_save(flags);
 266        rcu_preempt_qs(cpu);
 267        local_irq_restore(flags);
 268}
 269
 270/*
 271 * Check for preempted RCU readers blocking the current grace period
 272 * for the specified rcu_node structure.  If the caller needs a reliable
 273 * answer, it must hold the rcu_node's ->lock.
 274 */
 275static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
 276{
 277        return rnp->gp_tasks != NULL;
 278}
 279
 280/*
 281 * Record a quiescent state for all tasks that were previously queued
 282 * on the specified rcu_node structure and that were blocking the current
 283 * RCU grace period.  The caller must hold the specified rnp->lock with
 284 * irqs disabled, and this lock is released upon return, but irqs remain
 285 * disabled.
 286 */
 287static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
 288        __releases(rnp->lock)
 289{
 290        unsigned long mask;
 291        struct rcu_node *rnp_p;
 292
 293        if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
 294                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 295                return;  /* Still need more quiescent states! */
 296        }
 297
 298        rnp_p = rnp->parent;
 299        if (rnp_p == NULL) {
 300                /*
 301                 * Either there is only one rcu_node in the tree,
 302                 * or tasks were kicked up to root rcu_node due to
 303                 * CPUs going offline.
 304                 */
 305                rcu_report_qs_rsp(&rcu_preempt_state, flags);
 306                return;
 307        }
 308
 309        /* Report up the rest of the hierarchy. */
 310        mask = rnp->grpmask;
 311        raw_spin_unlock(&rnp->lock);    /* irqs remain disabled. */
 312        raw_spin_lock(&rnp_p->lock);    /* irqs already disabled. */
 313        rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
 314}
 315
 316/*
 317 * Advance a ->blkd_tasks-list pointer to the next entry, instead
 318 * returning NULL if at the end of the list.
 319 */
 320static struct list_head *rcu_next_node_entry(struct task_struct *t,
 321                                             struct rcu_node *rnp)
 322{
 323        struct list_head *np;
 324
 325        np = t->rcu_node_entry.next;
 326        if (np == &rnp->blkd_tasks)
 327                np = NULL;
 328        return np;
 329}
 330
 331/*
 332 * Handle special cases during rcu_read_unlock(), such as needing to
 333 * notify RCU core processing or task having blocked during the RCU
 334 * read-side critical section.
 335 */
 336void rcu_read_unlock_special(struct task_struct *t)
 337{
 338        int empty;
 339        int empty_exp;
 340        int empty_exp_now;
 341        unsigned long flags;
 342        struct list_head *np;
 343#ifdef CONFIG_RCU_BOOST
 344        struct rt_mutex *rbmp = NULL;
 345#endif /* #ifdef CONFIG_RCU_BOOST */
 346        struct rcu_node *rnp;
 347        int special;
 348
 349        /* NMI handlers cannot block and cannot safely manipulate state. */
 350        if (in_nmi())
 351                return;
 352
 353        local_irq_save(flags);
 354
 355        /*
 356         * If RCU core is waiting for this CPU to exit critical section,
 357         * let it know that we have done so.
 358         */
 359        special = t->rcu_read_unlock_special;
 360        if (special & RCU_READ_UNLOCK_NEED_QS) {
 361                rcu_preempt_qs(smp_processor_id());
 362        }
 363
 364        /* Hardware IRQ handlers cannot block. */
 365        if (in_irq() || in_serving_softirq()) {
 366                local_irq_restore(flags);
 367                return;
 368        }
 369
 370        /* Clean up if blocked during RCU read-side critical section. */
 371        if (special & RCU_READ_UNLOCK_BLOCKED) {
 372                t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
 373
 374                /*
 375                 * Remove this task from the list it blocked on.  The
 376                 * task can migrate while we acquire the lock, but at
 377                 * most one time.  So at most two passes through loop.
 378                 */
 379                for (;;) {
 380                        rnp = t->rcu_blocked_node;
 381                        raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
 382                        if (rnp == t->rcu_blocked_node)
 383                                break;
 384                        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
 385                }
 386                empty = !rcu_preempt_blocked_readers_cgp(rnp);
 387                empty_exp = !rcu_preempted_readers_exp(rnp);
 388                smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
 389                np = rcu_next_node_entry(t, rnp);
 390                list_del_init(&t->rcu_node_entry);
 391                t->rcu_blocked_node = NULL;
 392                trace_rcu_unlock_preempted_task("rcu_preempt",
 393                                                rnp->gpnum, t->pid);
 394                if (&t->rcu_node_entry == rnp->gp_tasks)
 395                        rnp->gp_tasks = np;
 396                if (&t->rcu_node_entry == rnp->exp_tasks)
 397                        rnp->exp_tasks = np;
 398#ifdef CONFIG_RCU_BOOST
 399                if (&t->rcu_node_entry == rnp->boost_tasks)
 400                        rnp->boost_tasks = np;
 401                /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
 402                if (t->rcu_boost_mutex) {
 403                        rbmp = t->rcu_boost_mutex;
 404                        t->rcu_boost_mutex = NULL;
 405                }
 406#endif /* #ifdef CONFIG_RCU_BOOST */
 407
 408                /*
 409                 * If this was the last task on the current list, and if
 410                 * we aren't waiting on any CPUs, report the quiescent state.
 411                 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
 412                 * so we must take a snapshot of the expedited state.
 413                 */
 414                empty_exp_now = !rcu_preempted_readers_exp(rnp);
 415                if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
 416                        trace_rcu_quiescent_state_report("preempt_rcu",
 417                                                         rnp->gpnum,
 418                                                         0, rnp->qsmask,
 419                                                         rnp->level,
 420                                                         rnp->grplo,
 421                                                         rnp->grphi,
 422                                                         !!rnp->gp_tasks);
 423                        rcu_report_unblock_qs_rnp(rnp, flags);
 424                } else {
 425                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 426                }
 427
 428#ifdef CONFIG_RCU_BOOST
 429                /* Unboost if we were boosted. */
 430                if (rbmp)
 431                        rt_mutex_unlock(rbmp);
 432#endif /* #ifdef CONFIG_RCU_BOOST */
 433
 434                /*
 435                 * If this was the last task on the expedited lists,
 436                 * then we need to report up the rcu_node hierarchy.
 437                 */
 438                if (!empty_exp && empty_exp_now)
 439                        rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
 440        } else {
 441                local_irq_restore(flags);
 442        }
 443}
 444
 445#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
 446
 447/*
 448 * Dump detailed information for all tasks blocking the current RCU
 449 * grace period on the specified rcu_node structure.
 450 */
 451static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
 452{
 453        unsigned long flags;
 454        struct task_struct *t;
 455
 456        raw_spin_lock_irqsave(&rnp->lock, flags);
 457        if (!rcu_preempt_blocked_readers_cgp(rnp)) {
 458                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 459                return;
 460        }
 461        t = list_entry(rnp->gp_tasks,
 462                       struct task_struct, rcu_node_entry);
 463        list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
 464                sched_show_task(t);
 465        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 466}
 467
 468/*
 469 * Dump detailed information for all tasks blocking the current RCU
 470 * grace period.
 471 */
 472static void rcu_print_detail_task_stall(struct rcu_state *rsp)
 473{
 474        struct rcu_node *rnp = rcu_get_root(rsp);
 475
 476        rcu_print_detail_task_stall_rnp(rnp);
 477        rcu_for_each_leaf_node(rsp, rnp)
 478                rcu_print_detail_task_stall_rnp(rnp);
 479}
 480
 481#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
 482
 483static void rcu_print_detail_task_stall(struct rcu_state *rsp)
 484{
 485}
 486
 487#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
 488
 489#ifdef CONFIG_RCU_CPU_STALL_INFO
 490
 491static void rcu_print_task_stall_begin(struct rcu_node *rnp)
 492{
 493        printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
 494               rnp->level, rnp->grplo, rnp->grphi);
 495}
 496
 497static void rcu_print_task_stall_end(void)
 498{
 499        printk(KERN_CONT "\n");
 500}
 501
 502#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
 503
 504static void rcu_print_task_stall_begin(struct rcu_node *rnp)
 505{
 506}
 507
 508static void rcu_print_task_stall_end(void)
 509{
 510}
 511
 512#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
 513
 514/*
 515 * Scan the current list of tasks blocked within RCU read-side critical
 516 * sections, printing out the tid of each.
 517 */
 518static int rcu_print_task_stall(struct rcu_node *rnp)
 519{
 520        struct task_struct *t;
 521        int ndetected = 0;
 522
 523        if (!rcu_preempt_blocked_readers_cgp(rnp))
 524                return 0;
 525        rcu_print_task_stall_begin(rnp);
 526        t = list_entry(rnp->gp_tasks,
 527                       struct task_struct, rcu_node_entry);
 528        list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
 529                printk(KERN_CONT " P%d", t->pid);
 530                ndetected++;
 531        }
 532        rcu_print_task_stall_end();
 533        return ndetected;
 534}
 535
 536/*
 537 * Check that the list of blocked tasks for the newly completed grace
 538 * period is in fact empty.  It is a serious bug to complete a grace
 539 * period that still has RCU readers blocked!  This function must be
 540 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
 541 * must be held by the caller.
 542 *
 543 * Also, if there are blocked tasks on the list, they automatically
 544 * block the newly created grace period, so set up ->gp_tasks accordingly.
 545 */
 546static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
 547{
 548        WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
 549        if (!list_empty(&rnp->blkd_tasks))
 550                rnp->gp_tasks = rnp->blkd_tasks.next;
 551        WARN_ON_ONCE(rnp->qsmask);
 552}
 553
 554#ifdef CONFIG_HOTPLUG_CPU
 555
 556/*
 557 * Handle tasklist migration for case in which all CPUs covered by the
 558 * specified rcu_node have gone offline.  Move them up to the root
 559 * rcu_node.  The reason for not just moving them to the immediate
 560 * parent is to remove the need for rcu_read_unlock_special() to
 561 * make more than two attempts to acquire the target rcu_node's lock.
 562 * Returns true if there were tasks blocking the current RCU grace
 563 * period.
 564 *
 565 * Returns 1 if there was previously a task blocking the current grace
 566 * period on the specified rcu_node structure.
 567 *
 568 * The caller must hold rnp->lock with irqs disabled.
 569 */
 570static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
 571                                     struct rcu_node *rnp,
 572                                     struct rcu_data *rdp)
 573{
 574        struct list_head *lp;
 575        struct list_head *lp_root;
 576        int retval = 0;
 577        struct rcu_node *rnp_root = rcu_get_root(rsp);
 578        struct task_struct *t;
 579
 580        if (rnp == rnp_root) {
 581                WARN_ONCE(1, "Last CPU thought to be offlined?");
 582                return 0;  /* Shouldn't happen: at least one CPU online. */
 583        }
 584
 585        /* If we are on an internal node, complain bitterly. */
 586        WARN_ON_ONCE(rnp != rdp->mynode);
 587
 588        /*
 589         * Move tasks up to root rcu_node.  Don't try to get fancy for
 590         * this corner-case operation -- just put this node's tasks
 591         * at the head of the root node's list, and update the root node's
 592         * ->gp_tasks and ->exp_tasks pointers to those of this node's,
 593         * if non-NULL.  This might result in waiting for more tasks than
 594         * absolutely necessary, but this is a good performance/complexity
 595         * tradeoff.
 596         */
 597        if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
 598                retval |= RCU_OFL_TASKS_NORM_GP;
 599        if (rcu_preempted_readers_exp(rnp))
 600                retval |= RCU_OFL_TASKS_EXP_GP;
 601        lp = &rnp->blkd_tasks;
 602        lp_root = &rnp_root->blkd_tasks;
 603        while (!list_empty(lp)) {
 604                t = list_entry(lp->next, typeof(*t), rcu_node_entry);
 605                raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
 606                list_del(&t->rcu_node_entry);
 607                t->rcu_blocked_node = rnp_root;
 608                list_add(&t->rcu_node_entry, lp_root);
 609                if (&t->rcu_node_entry == rnp->gp_tasks)
 610                        rnp_root->gp_tasks = rnp->gp_tasks;
 611                if (&t->rcu_node_entry == rnp->exp_tasks)
 612                        rnp_root->exp_tasks = rnp->exp_tasks;
 613#ifdef CONFIG_RCU_BOOST
 614                if (&t->rcu_node_entry == rnp->boost_tasks)
 615                        rnp_root->boost_tasks = rnp->boost_tasks;
 616#endif /* #ifdef CONFIG_RCU_BOOST */
 617                raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
 618        }
 619
 620        rnp->gp_tasks = NULL;
 621        rnp->exp_tasks = NULL;
 622#ifdef CONFIG_RCU_BOOST
 623        rnp->boost_tasks = NULL;
 624        /*
 625         * In case root is being boosted and leaf was not.  Make sure
 626         * that we boost the tasks blocking the current grace period
 627         * in this case.
 628         */
 629        raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
 630        if (rnp_root->boost_tasks != NULL &&
 631            rnp_root->boost_tasks != rnp_root->gp_tasks &&
 632            rnp_root->boost_tasks != rnp_root->exp_tasks)
 633                rnp_root->boost_tasks = rnp_root->gp_tasks;
 634        raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
 635#endif /* #ifdef CONFIG_RCU_BOOST */
 636
 637        return retval;
 638}
 639
 640#endif /* #ifdef CONFIG_HOTPLUG_CPU */
 641
 642/*
 643 * Check for a quiescent state from the current CPU.  When a task blocks,
 644 * the task is recorded in the corresponding CPU's rcu_node structure,
 645 * which is checked elsewhere.
 646 *
 647 * Caller must disable hard irqs.
 648 */
 649static void rcu_preempt_check_callbacks(int cpu)
 650{
 651        struct task_struct *t = current;
 652
 653        if (t->rcu_read_lock_nesting == 0) {
 654                rcu_preempt_qs(cpu);
 655                return;
 656        }
 657        if (t->rcu_read_lock_nesting > 0 &&
 658            per_cpu(rcu_preempt_data, cpu).qs_pending)
 659                t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 660}
 661
 662#ifdef CONFIG_RCU_BOOST
 663
 664static void rcu_preempt_do_callbacks(void)
 665{
 666        rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
 667}
 668
 669#endif /* #ifdef CONFIG_RCU_BOOST */
 670
 671/*
 672 * Queue a preemptible-RCU callback for invocation after a grace period.
 673 */
 674void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 675{
 676        __call_rcu(head, func, &rcu_preempt_state, -1, 0);
 677}
 678EXPORT_SYMBOL_GPL(call_rcu);
 679
 680/*
 681 * Queue an RCU callback for lazy invocation after a grace period.
 682 * This will likely be later named something like "call_rcu_lazy()",
 683 * but this change will require some way of tagging the lazy RCU
 684 * callbacks in the list of pending callbacks.  Until then, this
 685 * function may only be called from __kfree_rcu().
 686 */
 687void kfree_call_rcu(struct rcu_head *head,
 688                    void (*func)(struct rcu_head *rcu))
 689{
 690        __call_rcu(head, func, &rcu_preempt_state, -1, 1);
 691}
 692EXPORT_SYMBOL_GPL(kfree_call_rcu);
 693
 694/**
 695 * synchronize_rcu - wait until a grace period has elapsed.
 696 *
 697 * Control will return to the caller some time after a full grace
 698 * period has elapsed, in other words after all currently executing RCU
 699 * read-side critical sections have completed.  Note, however, that
 700 * upon return from synchronize_rcu(), the caller might well be executing
 701 * concurrently with new RCU read-side critical sections that began while
 702 * synchronize_rcu() was waiting.  RCU read-side critical sections are
 703 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
 704 *
 705 * See the description of synchronize_sched() for more detailed information
 706 * on memory ordering guarantees.
 707 */
 708void synchronize_rcu(void)
 709{
 710        rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
 711                           !lock_is_held(&rcu_lock_map) &&
 712                           !lock_is_held(&rcu_sched_lock_map),
 713                           "Illegal synchronize_rcu() in RCU read-side critical section");
 714        if (!rcu_scheduler_active)
 715                return;
 716        if (rcu_expedited)
 717                synchronize_rcu_expedited();
 718        else
 719                wait_rcu_gp(call_rcu);
 720}
 721EXPORT_SYMBOL_GPL(synchronize_rcu);
 722
 723static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
 724static unsigned long sync_rcu_preempt_exp_count;
 725static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
 726
 727/*
 728 * Return non-zero if there are any tasks in RCU read-side critical
 729 * sections blocking the current preemptible-RCU expedited grace period.
 730 * If there is no preemptible-RCU expedited grace period currently in
 731 * progress, returns zero unconditionally.
 732 */
 733static int rcu_preempted_readers_exp(struct rcu_node *rnp)
 734{
 735        return rnp->exp_tasks != NULL;
 736}
 737
 738/*
 739 * return non-zero if there is no RCU expedited grace period in progress
 740 * for the specified rcu_node structure, in other words, if all CPUs and
 741 * tasks covered by the specified rcu_node structure have done their bit
 742 * for the current expedited grace period.  Works only for preemptible
 743 * RCU -- other RCU implementation use other means.
 744 *
 745 * Caller must hold sync_rcu_preempt_exp_mutex.
 746 */
 747static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
 748{
 749        return !rcu_preempted_readers_exp(rnp) &&
 750               ACCESS_ONCE(rnp->expmask) == 0;
 751}
 752
 753/*
 754 * Report the exit from RCU read-side critical section for the last task
 755 * that queued itself during or before the current expedited preemptible-RCU
 756 * grace period.  This event is reported either to the rcu_node structure on
 757 * which the task was queued or to one of that rcu_node structure's ancestors,
 758 * recursively up the tree.  (Calm down, calm down, we do the recursion
 759 * iteratively!)
 760 *
 761 * Most callers will set the "wake" flag, but the task initiating the
 762 * expedited grace period need not wake itself.
 763 *
 764 * Caller must hold sync_rcu_preempt_exp_mutex.
 765 */
 766static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
 767                               bool wake)
 768{
 769        unsigned long flags;
 770        unsigned long mask;
 771
 772        raw_spin_lock_irqsave(&rnp->lock, flags);
 773        for (;;) {
 774                if (!sync_rcu_preempt_exp_done(rnp)) {
 775                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 776                        break;
 777                }
 778                if (rnp->parent == NULL) {
 779                        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 780                        if (wake)
 781                                wake_up(&sync_rcu_preempt_exp_wq);
 782                        break;
 783                }
 784                mask = rnp->grpmask;
 785                raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
 786                rnp = rnp->parent;
 787                raw_spin_lock(&rnp->lock); /* irqs already disabled */
 788                rnp->expmask &= ~mask;
 789        }
 790}
 791
 792/*
 793 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
 794 * grace period for the specified rcu_node structure.  If there are no such
 795 * tasks, report it up the rcu_node hierarchy.
 796 *
 797 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
 798 * CPU hotplug operations.
 799 */
 800static void
 801sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
 802{
 803        unsigned long flags;
 804        int must_wait = 0;
 805
 806        raw_spin_lock_irqsave(&rnp->lock, flags);
 807        if (list_empty(&rnp->blkd_tasks)) {
 808                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 809        } else {
 810                rnp->exp_tasks = rnp->blkd_tasks.next;
 811                rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
 812                must_wait = 1;
 813        }
 814        if (!must_wait)
 815                rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
 816}
 817
 818/**
 819 * synchronize_rcu_expedited - Brute-force RCU grace period
 820 *
 821 * Wait for an RCU-preempt grace period, but expedite it.  The basic
 822 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
 823 * the ->blkd_tasks lists and wait for this list to drain.  This consumes
 824 * significant time on all CPUs and is unfriendly to real-time workloads,
 825 * so is thus not recommended for any sort of common-case code.
 826 * In fact, if you are using synchronize_rcu_expedited() in a loop,
 827 * please restructure your code to batch your updates, and then Use a
 828 * single synchronize_rcu() instead.
 829 *
 830 * Note that it is illegal to call this function while holding any lock
 831 * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
 832 * to call this function from a CPU-hotplug notifier.  Failing to observe
 833 * these restriction will result in deadlock.
 834 */
 835void synchronize_rcu_expedited(void)
 836{
 837        unsigned long flags;
 838        struct rcu_node *rnp;
 839        struct rcu_state *rsp = &rcu_preempt_state;
 840        unsigned long snap;
 841        int trycount = 0;
 842
 843        smp_mb(); /* Caller's modifications seen first by other CPUs. */
 844        snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
 845        smp_mb(); /* Above access cannot bleed into critical section. */
 846
 847        /*
 848         * Block CPU-hotplug operations.  This means that any CPU-hotplug
 849         * operation that finds an rcu_node structure with tasks in the
 850         * process of being boosted will know that all tasks blocking
 851         * this expedited grace period will already be in the process of
 852         * being boosted.  This simplifies the process of moving tasks
 853         * from leaf to root rcu_node structures.
 854         */
 855        get_online_cpus();
 856
 857        /*
 858         * Acquire lock, falling back to synchronize_rcu() if too many
 859         * lock-acquisition failures.  Of course, if someone does the
 860         * expedited grace period for us, just leave.
 861         */
 862        while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
 863                if (ULONG_CMP_LT(snap,
 864                    ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
 865                        put_online_cpus();
 866                        goto mb_ret; /* Others did our work for us. */
 867                }
 868                if (trycount++ < 10) {
 869                        udelay(trycount * num_online_cpus());
 870                } else {
 871                        put_online_cpus();
 872                        wait_rcu_gp(call_rcu);
 873                        return;
 874                }
 875        }
 876        if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
 877                put_online_cpus();
 878                goto unlock_mb_ret; /* Others did our work for us. */
 879        }
 880
 881        /* force all RCU readers onto ->blkd_tasks lists. */
 882        synchronize_sched_expedited();
 883
 884        /* Initialize ->expmask for all non-leaf rcu_node structures. */
 885        rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
 886                raw_spin_lock_irqsave(&rnp->lock, flags);
 887                rnp->expmask = rnp->qsmaskinit;
 888                raw_spin_unlock_irqrestore(&rnp->lock, flags);
 889        }
 890
 891        /* Snapshot current state of ->blkd_tasks lists. */
 892        rcu_for_each_leaf_node(rsp, rnp)
 893                sync_rcu_preempt_exp_init(rsp, rnp);
 894        if (NUM_RCU_NODES > 1)
 895                sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
 896
 897        put_online_cpus();
 898
 899        /* Wait for snapshotted ->blkd_tasks lists to drain. */
 900        rnp = rcu_get_root(rsp);
 901        wait_event(sync_rcu_preempt_exp_wq,
 902                   sync_rcu_preempt_exp_done(rnp));
 903
 904        /* Clean up and exit. */
 905        smp_mb(); /* ensure expedited GP seen before counter increment. */
 906        ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
 907unlock_mb_ret:
 908        mutex_unlock(&sync_rcu_preempt_exp_mutex);
 909mb_ret:
 910        smp_mb(); /* ensure subsequent action seen after grace period. */
 911}
 912EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 913
 914/**
 915 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 916 *
 917 * Note that this primitive does not necessarily wait for an RCU grace period
 918 * to complete.  For example, if there are no RCU callbacks queued anywhere
 919 * in the system, then rcu_barrier() is within its rights to return
 920 * immediately, without waiting for anything, much less an RCU grace period.
 921 */
 922void rcu_barrier(void)
 923{
 924        _rcu_barrier(&rcu_preempt_state);
 925}
 926EXPORT_SYMBOL_GPL(rcu_barrier);
 927
 928/*
 929 * Initialize preemptible RCU's state structures.
 930 */
 931static void __init __rcu_init_preempt(void)
 932{
 933        rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
 934}
 935
 936#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 937
 938static struct rcu_state *rcu_state = &rcu_sched_state;
 939
 940/*
 941 * Tell them what RCU they are running.
 942 */
 943static void __init rcu_bootup_announce(void)
 944{
 945        printk(KERN_INFO "Hierarchical RCU implementation.\n");
 946        rcu_bootup_announce_oddness();
 947}
 948
 949/*
 950 * Return the number of RCU batches processed thus far for debug & stats.
 951 */
 952long rcu_batches_completed(void)
 953{
 954        return rcu_batches_completed_sched();
 955}
 956EXPORT_SYMBOL_GPL(rcu_batches_completed);
 957
 958/*
 959 * Force a quiescent state for RCU, which, because there is no preemptible
 960 * RCU, becomes the same as rcu-sched.
 961 */
 962void rcu_force_quiescent_state(void)
 963{
 964        rcu_sched_force_quiescent_state();
 965}
 966EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
 967
 968/*
 969 * Because preemptible RCU does not exist, we never have to check for
 970 * CPUs being in quiescent states.
 971 */
 972static void rcu_preempt_note_context_switch(int cpu)
 973{
 974}
 975
 976/*
 977 * Because preemptible RCU does not exist, there are never any preempted
 978 * RCU readers.
 979 */
 980static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
 981{
 982        return 0;
 983}
 984
 985#ifdef CONFIG_HOTPLUG_CPU
 986
 987/* Because preemptible RCU does not exist, no quieting of tasks. */
 988static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
 989{
 990        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 991}
 992
 993#endif /* #ifdef CONFIG_HOTPLUG_CPU */
 994
 995/*
 996 * Because preemptible RCU does not exist, we never have to check for
 997 * tasks blocked within RCU read-side critical sections.
 998 */
 999static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1000{
1001}
1002
1003/*
1004 * Because preemptible RCU does not exist, we never have to check for
1005 * tasks blocked within RCU read-side critical sections.
1006 */
1007static int rcu_print_task_stall(struct rcu_node *rnp)
1008{
1009        return 0;
1010}
1011
1012/*
1013 * Because there is no preemptible RCU, there can be no readers blocked,
1014 * so there is no need to check for blocked tasks.  So check only for
1015 * bogus qsmask values.
1016 */
1017static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1018{
1019        WARN_ON_ONCE(rnp->qsmask);
1020}
1021
1022#ifdef CONFIG_HOTPLUG_CPU
1023
1024/*
1025 * Because preemptible RCU does not exist, it never needs to migrate
1026 * tasks that were blocked within RCU read-side critical sections, and
1027 * such non-existent tasks cannot possibly have been blocking the current
1028 * grace period.
1029 */
1030static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1031                                     struct rcu_node *rnp,
1032                                     struct rcu_data *rdp)
1033{
1034        return 0;
1035}
1036
1037#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1038
1039/*
1040 * Because preemptible RCU does not exist, it never has any callbacks
1041 * to check.
1042 */
1043static void rcu_preempt_check_callbacks(int cpu)
1044{
1045}
1046
1047/*
1048 * Queue an RCU callback for lazy invocation after a grace period.
1049 * This will likely be later named something like "call_rcu_lazy()",
1050 * but this change will require some way of tagging the lazy RCU
1051 * callbacks in the list of pending callbacks.  Until then, this
1052 * function may only be called from __kfree_rcu().
1053 *
1054 * Because there is no preemptible RCU, we use RCU-sched instead.
1055 */
1056void kfree_call_rcu(struct rcu_head *head,
1057                    void (*func)(struct rcu_head *rcu))
1058{
1059        __call_rcu(head, func, &rcu_sched_state, -1, 1);
1060}
1061EXPORT_SYMBOL_GPL(kfree_call_rcu);
1062
1063/*
1064 * Wait for an rcu-preempt grace period, but make it happen quickly.
1065 * But because preemptible RCU does not exist, map to rcu-sched.
1066 */
1067void synchronize_rcu_expedited(void)
1068{
1069        synchronize_sched_expedited();
1070}
1071EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1072
1073#ifdef CONFIG_HOTPLUG_CPU
1074
1075/*
1076 * Because preemptible RCU does not exist, there is never any need to
1077 * report on tasks preempted in RCU read-side critical sections during
1078 * expedited RCU grace periods.
1079 */
1080static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1081                               bool wake)
1082{
1083}
1084
1085#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1086
1087/*
1088 * Because preemptible RCU does not exist, rcu_barrier() is just
1089 * another name for rcu_barrier_sched().
1090 */
1091void rcu_barrier(void)
1092{
1093        rcu_barrier_sched();
1094}
1095EXPORT_SYMBOL_GPL(rcu_barrier);
1096
1097/*
1098 * Because preemptible RCU does not exist, it need not be initialized.
1099 */
1100static void __init __rcu_init_preempt(void)
1101{
1102}
1103
1104#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1105
1106#ifdef CONFIG_RCU_BOOST
1107
1108#include "rtmutex_common.h"
1109
1110#ifdef CONFIG_RCU_TRACE
1111
1112static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1113{
1114        if (list_empty(&rnp->blkd_tasks))
1115                rnp->n_balk_blkd_tasks++;
1116        else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1117                rnp->n_balk_exp_gp_tasks++;
1118        else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1119                rnp->n_balk_boost_tasks++;
1120        else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1121                rnp->n_balk_notblocked++;
1122        else if (rnp->gp_tasks != NULL &&
1123                 ULONG_CMP_LT(jiffies, rnp->boost_time))
1124                rnp->n_balk_notyet++;
1125        else
1126                rnp->n_balk_nos++;
1127}
1128
1129#else /* #ifdef CONFIG_RCU_TRACE */
1130
1131static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1132{
1133}
1134
1135#endif /* #else #ifdef CONFIG_RCU_TRACE */
1136
1137static void rcu_wake_cond(struct task_struct *t, int status)
1138{
1139        /*
1140         * If the thread is yielding, only wake it when this
1141         * is invoked from idle
1142         */
1143        if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1144                wake_up_process(t);
1145}
1146
1147/*
1148 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1149 * or ->boost_tasks, advancing the pointer to the next task in the
1150 * ->blkd_tasks list.
1151 *
1152 * Note that irqs must be enabled: boosting the task can block.
1153 * Returns 1 if there are more tasks needing to be boosted.
1154 */
1155static int rcu_boost(struct rcu_node *rnp)
1156{
1157        unsigned long flags;
1158        struct rt_mutex mtx;
1159        struct task_struct *t;
1160        struct list_head *tb;
1161
1162        if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1163                return 0;  /* Nothing left to boost. */
1164
1165        raw_spin_lock_irqsave(&rnp->lock, flags);
1166
1167        /*
1168         * Recheck under the lock: all tasks in need of boosting
1169         * might exit their RCU read-side critical sections on their own.
1170         */
1171        if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1172                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1173                return 0;
1174        }
1175
1176        /*
1177         * Preferentially boost tasks blocking expedited grace periods.
1178         * This cannot starve the normal grace periods because a second
1179         * expedited grace period must boost all blocked tasks, including
1180         * those blocking the pre-existing normal grace period.
1181         */
1182        if (rnp->exp_tasks != NULL) {
1183                tb = rnp->exp_tasks;
1184                rnp->n_exp_boosts++;
1185        } else {
1186                tb = rnp->boost_tasks;
1187                rnp->n_normal_boosts++;
1188        }
1189        rnp->n_tasks_boosted++;
1190
1191        /*
1192         * We boost task t by manufacturing an rt_mutex that appears to
1193         * be held by task t.  We leave a pointer to that rt_mutex where
1194         * task t can find it, and task t will release the mutex when it
1195         * exits its outermost RCU read-side critical section.  Then
1196         * simply acquiring this artificial rt_mutex will boost task
1197         * t's priority.  (Thanks to tglx for suggesting this approach!)
1198         *
1199         * Note that task t must acquire rnp->lock to remove itself from
1200         * the ->blkd_tasks list, which it will do from exit() if from
1201         * nowhere else.  We therefore are guaranteed that task t will
1202         * stay around at least until we drop rnp->lock.  Note that
1203         * rnp->lock also resolves races between our priority boosting
1204         * and task t's exiting its outermost RCU read-side critical
1205         * section.
1206         */
1207        t = container_of(tb, struct task_struct, rcu_node_entry);
1208        rt_mutex_init_proxy_locked(&mtx, t);
1209        t->rcu_boost_mutex = &mtx;
1210        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1211        rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
1212        rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
1213
1214        return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1215               ACCESS_ONCE(rnp->boost_tasks) != NULL;
1216}
1217
1218/*
1219 * Priority-boosting kthread.  One per leaf rcu_node and one for the
1220 * root rcu_node.
1221 */
1222static int rcu_boost_kthread(void *arg)
1223{
1224        struct rcu_node *rnp = (struct rcu_node *)arg;
1225        int spincnt = 0;
1226        int more2boost;
1227
1228        trace_rcu_utilization("Start boost kthread@init");
1229        for (;;) {
1230                rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1231                trace_rcu_utilization("End boost kthread@rcu_wait");
1232                rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1233                trace_rcu_utilization("Start boost kthread@rcu_wait");
1234                rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1235                more2boost = rcu_boost(rnp);
1236                if (more2boost)
1237                        spincnt++;
1238                else
1239                        spincnt = 0;
1240                if (spincnt > 10) {
1241                        rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1242                        trace_rcu_utilization("End boost kthread@rcu_yield");
1243                        schedule_timeout_interruptible(2);
1244                        trace_rcu_utilization("Start boost kthread@rcu_yield");
1245                        spincnt = 0;
1246                }
1247        }
1248        /* NOTREACHED */
1249        trace_rcu_utilization("End boost kthread@notreached");
1250        return 0;
1251}
1252
1253/*
1254 * Check to see if it is time to start boosting RCU readers that are
1255 * blocking the current grace period, and, if so, tell the per-rcu_node
1256 * kthread to start boosting them.  If there is an expedited grace
1257 * period in progress, it is always time to boost.
1258 *
1259 * The caller must hold rnp->lock, which this function releases.
1260 * The ->boost_kthread_task is immortal, so we don't need to worry
1261 * about it going away.
1262 */
1263static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1264{
1265        struct task_struct *t;
1266
1267        if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1268                rnp->n_balk_exp_gp_tasks++;
1269                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1270                return;
1271        }
1272        if (rnp->exp_tasks != NULL ||
1273            (rnp->gp_tasks != NULL &&
1274             rnp->boost_tasks == NULL &&
1275             rnp->qsmask == 0 &&
1276             ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1277                if (rnp->exp_tasks == NULL)
1278                        rnp->boost_tasks = rnp->gp_tasks;
1279                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1280                t = rnp->boost_kthread_task;
1281                if (t)
1282                        rcu_wake_cond(t, rnp->boost_kthread_status);
1283        } else {
1284                rcu_initiate_boost_trace(rnp);
1285                raw_spin_unlock_irqrestore(&rnp->lock, flags);
1286        }
1287}
1288
1289/*
1290 * Wake up the per-CPU kthread to invoke RCU callbacks.
1291 */
1292static void invoke_rcu_callbacks_kthread(void)
1293{
1294        unsigned long flags;
1295
1296        local_irq_save(flags);
1297        __this_cpu_write(rcu_cpu_has_work, 1);
1298        if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1299            current != __this_cpu_read(rcu_cpu_kthread_task)) {
1300                rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1301                              __this_cpu_read(rcu_cpu_kthread_status));
1302        }
1303        local_irq_restore(flags);
1304}
1305
1306/*
1307 * Is the current CPU running the RCU-callbacks kthread?
1308 * Caller must have preemption disabled.
1309 */
1310static bool rcu_is_callbacks_kthread(void)
1311{
1312        return __get_cpu_var(rcu_cpu_kthread_task) == current;
1313}
1314
1315#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1316
1317/*
1318 * Do priority-boost accounting for the start of a new grace period.
1319 */
1320static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1321{
1322        rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1323}
1324
1325/*
1326 * Create an RCU-boost kthread for the specified node if one does not
1327 * already exist.  We only create this kthread for preemptible RCU.
1328 * Returns zero if all is well, a negated errno otherwise.
1329 */
1330static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1331                                                 struct rcu_node *rnp)
1332{
1333        int rnp_index = rnp - &rsp->node[0];
1334        unsigned long flags;
1335        struct sched_param sp;
1336        struct task_struct *t;
1337
1338        if (&rcu_preempt_state != rsp)
1339                return 0;
1340
1341        if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
1342                return 0;
1343
1344        rsp->boost = 1;
1345        if (rnp->boost_kthread_task != NULL)
1346                return 0;
1347        t = kthread_create(rcu_boost_kthread, (void *)rnp,
1348                           "rcub/%d", rnp_index);
1349        if (IS_ERR(t))
1350                return PTR_ERR(t);
1351        raw_spin_lock_irqsave(&rnp->lock, flags);
1352        rnp->boost_kthread_task = t;
1353        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1354        sp.sched_priority = RCU_BOOST_PRIO;
1355        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1356        wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1357        return 0;
1358}
1359
1360static void rcu_kthread_do_work(void)
1361{
1362        rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
1363        rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1364        rcu_preempt_do_callbacks();
1365}
1366
1367static void rcu_cpu_kthread_setup(unsigned int cpu)
1368{
1369        struct sched_param sp;
1370
1371        sp.sched_priority = RCU_KTHREAD_PRIO;
1372        sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1373}
1374
1375static void rcu_cpu_kthread_park(unsigned int cpu)
1376{
1377        per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1378}
1379
1380static int rcu_cpu_kthread_should_run(unsigned int cpu)
1381{
1382        return __get_cpu_var(rcu_cpu_has_work);
1383}
1384
1385/*
1386 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1387 * RCU softirq used in flavors and configurations of RCU that do not
1388 * support RCU priority boosting.
1389 */
1390static void rcu_cpu_kthread(unsigned int cpu)
1391{
1392        unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status);
1393        char work, *workp = &__get_cpu_var(rcu_cpu_has_work);
1394        int spincnt;
1395
1396        for (spincnt = 0; spincnt < 10; spincnt++) {
1397                trace_rcu_utilization("Start CPU kthread@rcu_wait");
1398                local_bh_disable();
1399                *statusp = RCU_KTHREAD_RUNNING;
1400                this_cpu_inc(rcu_cpu_kthread_loops);
1401                local_irq_disable();
1402                work = *workp;
1403                *workp = 0;
1404                local_irq_enable();
1405                if (work)
1406                        rcu_kthread_do_work();
1407                local_bh_enable();
1408                if (*workp == 0) {
1409                        trace_rcu_utilization("End CPU kthread@rcu_wait");
1410                        *statusp = RCU_KTHREAD_WAITING;
1411                        return;
1412                }
1413        }
1414        *statusp = RCU_KTHREAD_YIELDING;
1415        trace_rcu_utilization("Start CPU kthread@rcu_yield");
1416        schedule_timeout_interruptible(2);
1417        trace_rcu_utilization("End CPU kthread@rcu_yield");
1418        *statusp = RCU_KTHREAD_WAITING;
1419}
1420
1421/*
1422 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1423 * served by the rcu_node in question.  The CPU hotplug lock is still
1424 * held, so the value of rnp->qsmaskinit will be stable.
1425 *
1426 * We don't include outgoingcpu in the affinity set, use -1 if there is
1427 * no outgoing CPU.  If there are no CPUs left in the affinity set,
1428 * this function allows the kthread to execute on any CPU.
1429 */
1430static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1431{
1432        struct task_struct *t = rnp->boost_kthread_task;
1433        unsigned long mask = rnp->qsmaskinit;
1434        cpumask_var_t cm;
1435        int cpu;
1436
1437        if (!t)
1438                return;
1439        if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1440                return;
1441        for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1442                if ((mask & 0x1) && cpu != outgoingcpu)
1443                        cpumask_set_cpu(cpu, cm);
1444        if (cpumask_weight(cm) == 0) {
1445                cpumask_setall(cm);
1446                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1447                        cpumask_clear_cpu(cpu, cm);
1448                WARN_ON_ONCE(cpumask_weight(cm) == 0);
1449        }
1450        set_cpus_allowed_ptr(t, cm);
1451        free_cpumask_var(cm);
1452}
1453
1454static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1455        .store                  = &rcu_cpu_kthread_task,
1456        .thread_should_run      = rcu_cpu_kthread_should_run,
1457        .thread_fn              = rcu_cpu_kthread,
1458        .thread_comm            = "rcuc/%u",
1459        .setup                  = rcu_cpu_kthread_setup,
1460        .park                   = rcu_cpu_kthread_park,
1461};
1462
1463/*
1464 * Spawn all kthreads -- called as soon as the scheduler is running.
1465 */
1466static int __init rcu_spawn_kthreads(void)
1467{
1468        struct rcu_node *rnp;
1469        int cpu;
1470
1471        rcu_scheduler_fully_active = 1;
1472        for_each_possible_cpu(cpu)
1473                per_cpu(rcu_cpu_has_work, cpu) = 0;
1474        BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1475        rnp = rcu_get_root(rcu_state);
1476        (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1477        if (NUM_RCU_NODES > 1) {
1478                rcu_for_each_leaf_node(rcu_state, rnp)
1479                        (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1480        }
1481        return 0;
1482}
1483early_initcall(rcu_spawn_kthreads);
1484
1485static void __cpuinit rcu_prepare_kthreads(int cpu)
1486{
1487        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1488        struct rcu_node *rnp = rdp->mynode;
1489
1490        /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1491        if (rcu_scheduler_fully_active)
1492                (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1493}
1494
1495#else /* #ifdef CONFIG_RCU_BOOST */
1496
1497static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1498{
1499        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1500}
1501
1502static void invoke_rcu_callbacks_kthread(void)
1503{
1504        WARN_ON_ONCE(1);
1505}
1506
1507static bool rcu_is_callbacks_kthread(void)
1508{
1509        return false;
1510}
1511
1512static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1513{
1514}
1515
1516static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1517{
1518}
1519
1520static int __init rcu_scheduler_really_started(void)
1521{
1522        rcu_scheduler_fully_active = 1;
1523        return 0;
1524}
1525early_initcall(rcu_scheduler_really_started);
1526
1527static void __cpuinit rcu_prepare_kthreads(int cpu)
1528{
1529}
1530
1531#endif /* #else #ifdef CONFIG_RCU_BOOST */
1532
1533#if !defined(CONFIG_RCU_FAST_NO_HZ)
1534
1535/*
1536 * Check to see if any future RCU-related work will need to be done
1537 * by the current CPU, even if none need be done immediately, returning
1538 * 1 if so.  This function is part of the RCU implementation; it is -not-
1539 * an exported member of the RCU API.
1540 *
1541 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1542 * any flavor of RCU.
1543 */
1544int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1545{
1546        *delta_jiffies = ULONG_MAX;
1547        return rcu_cpu_has_callbacks(cpu, NULL);
1548}
1549
1550/*
1551 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1552 * after it.
1553 */
1554static void rcu_cleanup_after_idle(int cpu)
1555{
1556}
1557
1558/*
1559 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1560 * is nothing.
1561 */
1562static void rcu_prepare_for_idle(int cpu)
1563{
1564}
1565
1566/*
1567 * Don't bother keeping a running count of the number of RCU callbacks
1568 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1569 */
1570static void rcu_idle_count_callbacks_posted(void)
1571{
1572}
1573
1574#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1575
1576/*
1577 * This code is invoked when a CPU goes idle, at which point we want
1578 * to have the CPU do everything required for RCU so that it can enter
1579 * the energy-efficient dyntick-idle mode.  This is handled by a
1580 * state machine implemented by rcu_prepare_for_idle() below.
1581 *
1582 * The following three proprocessor symbols control this state machine:
1583 *
1584 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1585 *      to sleep in dyntick-idle mode with RCU callbacks pending.  This
1586 *      is sized to be roughly one RCU grace period.  Those energy-efficiency
1587 *      benchmarkers who might otherwise be tempted to set this to a large
1588 *      number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1589 *      system.  And if you are -that- concerned about energy efficiency,
1590 *      just power the system down and be done with it!
1591 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1592 *      permitted to sleep in dyntick-idle mode with only lazy RCU
1593 *      callbacks pending.  Setting this too high can OOM your system.
1594 *
1595 * The values below work well in practice.  If future workloads require
1596 * adjustment, they can be converted into kernel config parameters, though
1597 * making the state machine smarter might be a better option.
1598 */
1599#define RCU_IDLE_GP_DELAY 4             /* Roughly one grace period. */
1600#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1601
1602static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1603module_param(rcu_idle_gp_delay, int, 0644);
1604static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1605module_param(rcu_idle_lazy_gp_delay, int, 0644);
1606
1607extern int tick_nohz_enabled;
1608
1609/*
1610 * Try to advance callbacks for all flavors of RCU on the current CPU.
1611 * Afterwards, if there are any callbacks ready for immediate invocation,
1612 * return true.
1613 */
1614static bool rcu_try_advance_all_cbs(void)
1615{
1616        bool cbs_ready = false;
1617        struct rcu_data *rdp;
1618        struct rcu_node *rnp;
1619        struct rcu_state *rsp;
1620
1621        for_each_rcu_flavor(rsp) {
1622                rdp = this_cpu_ptr(rsp->rda);
1623                rnp = rdp->mynode;
1624
1625                /*
1626                 * Don't bother checking unless a grace period has
1627                 * completed since we last checked and there are
1628                 * callbacks not yet ready to invoke.
1629                 */
1630                if (rdp->completed != rnp->completed &&
1631                    rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1632                        rcu_process_gp_end(rsp, rdp);
1633
1634                if (cpu_has_callbacks_ready_to_invoke(rdp))
1635                        cbs_ready = true;
1636        }
1637        return cbs_ready;
1638}
1639
1640/*
1641 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1642 * to invoke.  If the CPU has callbacks, try to advance them.  Tell the
1643 * caller to set the timeout based on whether or not there are non-lazy
1644 * callbacks.
1645 *
1646 * The caller must have disabled interrupts.
1647 */
1648int rcu_needs_cpu(int cpu, unsigned long *dj)
1649{
1650        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1651
1652        /* Snapshot to detect later posting of non-lazy callback. */
1653        rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1654
1655        /* If no callbacks, RCU doesn't need the CPU. */
1656        if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
1657                *dj = ULONG_MAX;
1658                return 0;
1659        }
1660
1661        /* Attempt to advance callbacks. */
1662        if (rcu_try_advance_all_cbs()) {
1663                /* Some ready to invoke, so initiate later invocation. */
1664                invoke_rcu_core();
1665                return 1;
1666        }
1667        rdtp->last_accelerate = jiffies;
1668
1669        /* Request timer delay depending on laziness, and round. */
1670        if (!rdtp->all_lazy) {
1671                *dj = round_up(rcu_idle_gp_delay + jiffies,
1672                               rcu_idle_gp_delay) - jiffies;
1673        } else {
1674                *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1675        }
1676        return 0;
1677}
1678
1679/*
1680 * Prepare a CPU for idle from an RCU perspective.  The first major task
1681 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1682 * The second major task is to check to see if a non-lazy callback has
1683 * arrived at a CPU that previously had only lazy callbacks.  The third
1684 * major task is to accelerate (that is, assign grace-period numbers to)
1685 * any recently arrived callbacks.
1686 *
1687 * The caller must have disabled interrupts.
1688 */
1689static void rcu_prepare_for_idle(int cpu)
1690{
1691        struct rcu_data *rdp;
1692        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1693        struct rcu_node *rnp;
1694        struct rcu_state *rsp;
1695        int tne;
1696
1697        /* Handle nohz enablement switches conservatively. */
1698        tne = ACCESS_ONCE(tick_nohz_enabled);
1699        if (tne != rdtp->tick_nohz_enabled_snap) {
1700                if (rcu_cpu_has_callbacks(cpu, NULL))
1701                        invoke_rcu_core(); /* force nohz to see update. */
1702                rdtp->tick_nohz_enabled_snap = tne;
1703                return;
1704        }
1705        if (!tne)
1706                return;
1707
1708        /* If this is a no-CBs CPU, no callbacks, just return. */
1709        if (rcu_is_nocb_cpu(cpu))
1710                return;
1711
1712        /*
1713         * If a non-lazy callback arrived at a CPU having only lazy
1714         * callbacks, invoke RCU core for the side-effect of recalculating
1715         * idle duration on re-entry to idle.
1716         */
1717        if (rdtp->all_lazy &&
1718            rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1719                invoke_rcu_core();
1720                return;
1721        }
1722
1723        /*
1724         * If we have not yet accelerated this jiffy, accelerate all
1725         * callbacks on this CPU.
1726         */
1727        if (rdtp->last_accelerate == jiffies)
1728                return;
1729        rdtp->last_accelerate = jiffies;
1730        for_each_rcu_flavor(rsp) {
1731                rdp = per_cpu_ptr(rsp->rda, cpu);
1732                if (!*rdp->nxttail[RCU_DONE_TAIL])
1733                        continue;
1734                rnp = rdp->mynode;
1735                raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1736                rcu_accelerate_cbs(rsp, rnp, rdp);
1737                raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1738        }
1739}
1740
1741/*
1742 * Clean up for exit from idle.  Attempt to advance callbacks based on
1743 * any grace periods that elapsed while the CPU was idle, and if any
1744 * callbacks are now ready to invoke, initiate invocation.
1745 */
1746static void rcu_cleanup_after_idle(int cpu)
1747{
1748        struct rcu_data *rdp;
1749        struct rcu_state *rsp;
1750
1751        if (rcu_is_nocb_cpu(cpu))
1752                return;
1753        rcu_try_advance_all_cbs();
1754        for_each_rcu_flavor(rsp) {
1755                rdp = per_cpu_ptr(rsp->rda, cpu);
1756                if (cpu_has_callbacks_ready_to_invoke(rdp))
1757                        invoke_rcu_core();
1758        }
1759}
1760
1761/*
1762 * Keep a running count of the number of non-lazy callbacks posted
1763 * on this CPU.  This running counter (which is never decremented) allows
1764 * rcu_prepare_for_idle() to detect when something out of the idle loop
1765 * posts a callback, even if an equal number of callbacks are invoked.
1766 * Of course, callbacks should only be posted from within a trace event
1767 * designed to be called from idle or from within RCU_NONIDLE().
1768 */
1769static void rcu_idle_count_callbacks_posted(void)
1770{
1771        __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1772}
1773
1774/*
1775 * Data for flushing lazy RCU callbacks at OOM time.
1776 */
1777static atomic_t oom_callback_count;
1778static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1779
1780/*
1781 * RCU OOM callback -- decrement the outstanding count and deliver the
1782 * wake-up if we are the last one.
1783 */
1784static void rcu_oom_callback(struct rcu_head *rhp)
1785{
1786        if (atomic_dec_and_test(&oom_callback_count))
1787                wake_up(&oom_callback_wq);
1788}
1789
1790/*
1791 * Post an rcu_oom_notify callback on the current CPU if it has at
1792 * least one lazy callback.  This will unnecessarily post callbacks
1793 * to CPUs that already have a non-lazy callback at the end of their
1794 * callback list, but this is an infrequent operation, so accept some
1795 * extra overhead to keep things simple.
1796 */
1797static void rcu_oom_notify_cpu(void *unused)
1798{
1799        struct rcu_state *rsp;
1800        struct rcu_data *rdp;
1801
1802        for_each_rcu_flavor(rsp) {
1803                rdp = __this_cpu_ptr(rsp->rda);
1804                if (rdp->qlen_lazy != 0) {
1805                        atomic_inc(&oom_callback_count);
1806                        rsp->call(&rdp->oom_head, rcu_oom_callback);
1807                }
1808        }
1809}
1810
1811/*
1812 * If low on memory, ensure that each CPU has a non-lazy callback.
1813 * This will wake up CPUs that have only lazy callbacks, in turn
1814 * ensuring that they free up the corresponding memory in a timely manner.
1815 * Because an uncertain amount of memory will be freed in some uncertain
1816 * timeframe, we do not claim to have freed anything.
1817 */
1818static int rcu_oom_notify(struct notifier_block *self,
1819                          unsigned long notused, void *nfreed)
1820{
1821        int cpu;
1822
1823        /* Wait for callbacks from earlier instance to complete. */
1824        wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1825
1826        /*
1827         * Prevent premature wakeup: ensure that all increments happen
1828         * before there is a chance of the counter reaching zero.
1829         */
1830        atomic_set(&oom_callback_count, 1);
1831
1832        get_online_cpus();
1833        for_each_online_cpu(cpu) {
1834                smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1835                cond_resched();
1836        }
1837        put_online_cpus();
1838
1839        /* Unconditionally decrement: no need to wake ourselves up. */
1840        atomic_dec(&oom_callback_count);
1841
1842        return NOTIFY_OK;
1843}
1844
1845static struct notifier_block rcu_oom_nb = {
1846        .notifier_call = rcu_oom_notify
1847};
1848
1849static int __init rcu_register_oom_notifier(void)
1850{
1851        register_oom_notifier(&rcu_oom_nb);
1852        return 0;
1853}
1854early_initcall(rcu_register_oom_notifier);
1855
1856#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1857
1858#ifdef CONFIG_RCU_CPU_STALL_INFO
1859
1860#ifdef CONFIG_RCU_FAST_NO_HZ
1861
1862static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1863{
1864        struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1865        unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1866
1867        sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1868                rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1869                ulong2long(nlpd),
1870                rdtp->all_lazy ? 'L' : '.',
1871                rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1872}
1873
1874#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1875
1876static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1877{
1878        *cp = '\0';
1879}
1880
1881#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1882
1883/* Initiate the stall-info list. */
1884static void print_cpu_stall_info_begin(void)
1885{
1886        printk(KERN_CONT "\n");
1887}
1888
1889/*
1890 * Print out diagnostic information for the specified stalled CPU.
1891 *
1892 * If the specified CPU is aware of the current RCU grace period
1893 * (flavor specified by rsp), then print the number of scheduling
1894 * clock interrupts the CPU has taken during the time that it has
1895 * been aware.  Otherwise, print the number of RCU grace periods
1896 * that this CPU is ignorant of, for example, "1" if the CPU was
1897 * aware of the previous grace period.
1898 *
1899 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1900 */
1901static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1902{
1903        char fast_no_hz[72];
1904        struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1905        struct rcu_dynticks *rdtp = rdp->dynticks;
1906        char *ticks_title;
1907        unsigned long ticks_value;
1908
1909        if (rsp->gpnum == rdp->gpnum) {
1910                ticks_title = "ticks this GP";
1911                ticks_value = rdp->ticks_this_gp;
1912        } else {
1913                ticks_title = "GPs behind";
1914                ticks_value = rsp->gpnum - rdp->gpnum;
1915        }
1916        print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1917        printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1918               cpu, ticks_value, ticks_title,
1919               atomic_read(&rdtp->dynticks) & 0xfff,
1920               rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1921               rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1922               fast_no_hz);
1923}
1924
1925/* Terminate the stall-info list. */
1926static void print_cpu_stall_info_end(void)
1927{
1928        printk(KERN_ERR "\t");
1929}
1930
1931/* Zero ->ticks_this_gp for all flavors of RCU. */
1932static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1933{
1934        rdp->ticks_this_gp = 0;
1935        rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1936}
1937
1938/* Increment ->ticks_this_gp for all flavors of RCU. */
1939static void increment_cpu_stall_ticks(void)
1940{
1941        struct rcu_state *rsp;
1942
1943        for_each_rcu_flavor(rsp)
1944                __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
1945}
1946
1947#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1948
1949static void print_cpu_stall_info_begin(void)
1950{
1951        printk(KERN_CONT " {");
1952}
1953
1954static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1955{
1956        printk(KERN_CONT " %d", cpu);
1957}
1958
1959static void print_cpu_stall_info_end(void)
1960{
1961        printk(KERN_CONT "} ");
1962}
1963
1964static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1965{
1966}
1967
1968static void increment_cpu_stall_ticks(void)
1969{
1970}
1971
1972#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
1973
1974#ifdef CONFIG_RCU_NOCB_CPU
1975
1976/*
1977 * Offload callback processing from the boot-time-specified set of CPUs
1978 * specified by rcu_nocb_mask.  For each CPU in the set, there is a
1979 * kthread created that pulls the callbacks from the corresponding CPU,
1980 * waits for a grace period to elapse, and invokes the callbacks.
1981 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1982 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1983 * has been specified, in which case each kthread actively polls its
1984 * CPU.  (Which isn't so great for energy efficiency, but which does
1985 * reduce RCU's overhead on that CPU.)
1986 *
1987 * This is intended to be used in conjunction with Frederic Weisbecker's
1988 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1989 * running CPU-bound user-mode computations.
1990 *
1991 * Offloading of callback processing could also in theory be used as
1992 * an energy-efficiency measure because CPUs with no RCU callbacks
1993 * queued are more aggressive about entering dyntick-idle mode.
1994 */
1995
1996
1997/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1998static int __init rcu_nocb_setup(char *str)
1999{
2000        alloc_bootmem_cpumask_var(&rcu_nocb_mask);
2001        have_rcu_nocb_mask = true;
2002        cpulist_parse(str, rcu_nocb_mask);
2003        return 1;
2004}
2005__setup("rcu_nocbs=", rcu_nocb_setup);
2006
2007static int __init parse_rcu_nocb_poll(char *arg)
2008{
2009        rcu_nocb_poll = 1;
2010        return 0;
2011}
2012early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
2013
2014/*
2015 * Do any no-CBs CPUs need another grace period?
2016 *
2017 * Interrupts must be disabled.  If the caller does not hold the root
2018 * rnp_node structure's ->lock, the results are advisory only.
2019 */
2020static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2021{
2022        struct rcu_node *rnp = rcu_get_root(rsp);
2023
2024        return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
2025}
2026
2027/*
2028 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2029 * grace period.
2030 */
2031static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2032{
2033        wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2034}
2035
2036/*
2037 * Set the root rcu_node structure's ->need_future_gp field
2038 * based on the sum of those of all rcu_node structures.  This does
2039 * double-count the root rcu_node structure's requests, but this
2040 * is necessary to handle the possibility of a rcu_nocb_kthread()
2041 * having awakened during the time that the rcu_node structures
2042 * were being updated for the end of the previous grace period.
2043 */
2044static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2045{
2046        rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2047}
2048
2049static void rcu_init_one_nocb(struct rcu_node *rnp)
2050{
2051        init_waitqueue_head(&rnp->nocb_gp_wq[0]);
2052        init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2053}
2054
2055/* Is the specified CPU a no-CPUs CPU? */
2056bool rcu_is_nocb_cpu(int cpu)
2057{
2058        if (have_rcu_nocb_mask)
2059                return cpumask_test_cpu(cpu, rcu_nocb_mask);
2060        return false;
2061}
2062
2063/*
2064 * Enqueue the specified string of rcu_head structures onto the specified
2065 * CPU's no-CBs lists.  The CPU is specified by rdp, the head of the
2066 * string by rhp, and the tail of the string by rhtp.  The non-lazy/lazy
2067 * counts are supplied by rhcount and rhcount_lazy.
2068 *
2069 * If warranted, also wake up the kthread servicing this CPUs queues.
2070 */
2071static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2072                                    struct rcu_head *rhp,
2073                                    struct rcu_head **rhtp,
2074                                    int rhcount, int rhcount_lazy)
2075{
2076        int len;
2077        struct rcu_head **old_rhpp;
2078        struct task_struct *t;
2079
2080        /* Enqueue the callback on the nocb list and update counts. */
2081        old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2082        ACCESS_ONCE(*old_rhpp) = rhp;
2083        atomic_long_add(rhcount, &rdp->nocb_q_count);
2084        atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2085
2086        /* If we are not being polled and there is a kthread, awaken it ... */
2087        t = ACCESS_ONCE(rdp->nocb_kthread);
2088        if (rcu_nocb_poll | !t)
2089                return;
2090        len = atomic_long_read(&rdp->nocb_q_count);
2091        if (old_rhpp == &rdp->nocb_head) {
2092                wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */
2093                rdp->qlen_last_fqs_check = 0;
2094        } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2095                wake_up_process(t); /* ... or if many callbacks queued. */
2096                rdp->qlen_last_fqs_check = LONG_MAX / 2;
2097        }
2098        return;
2099}
2100
2101/*
2102 * This is a helper for __call_rcu(), which invokes this when the normal
2103 * callback queue is inoperable.  If this is not a no-CBs CPU, this
2104 * function returns failure back to __call_rcu(), which can complain
2105 * appropriately.
2106 *
2107 * Otherwise, this function queues the callback where the corresponding
2108 * "rcuo" kthread can find it.
2109 */
2110static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2111                            bool lazy)
2112{
2113
2114        if (!rcu_is_nocb_cpu(rdp->cpu))
2115                return 0;
2116        __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
2117        if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2118                trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2119                                         (unsigned long)rhp->func,
2120                                         rdp->qlen_lazy, rdp->qlen);
2121        else
2122                trace_rcu_callback(rdp->rsp->name, rhp,
2123                                   rdp->qlen_lazy, rdp->qlen);
2124        return 1;
2125}
2126
2127/*
2128 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2129 * not a no-CBs CPU.
2130 */
2131static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2132                                                     struct rcu_data *rdp)
2133{
2134        long ql = rsp->qlen;
2135        long qll = rsp->qlen_lazy;
2136
2137        /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2138        if (!rcu_is_nocb_cpu(smp_processor_id()))
2139                return 0;
2140        rsp->qlen = 0;
2141        rsp->qlen_lazy = 0;
2142
2143        /* First, enqueue the donelist, if any.  This preserves CB ordering. */
2144        if (rsp->orphan_donelist != NULL) {
2145                __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
2146                                        rsp->orphan_donetail, ql, qll);
2147                ql = qll = 0;
2148                rsp->orphan_donelist = NULL;
2149                rsp->orphan_donetail = &rsp->orphan_donelist;
2150        }
2151        if (rsp->orphan_nxtlist != NULL) {
2152                __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
2153                                        rsp->orphan_nxttail, ql, qll);
2154                ql = qll = 0;
2155                rsp->orphan_nxtlist = NULL;
2156                rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2157        }
2158        return 1;
2159}
2160
2161/*
2162 * If necessary, kick off a new grace period, and either way wait
2163 * for a subsequent grace period to complete.
2164 */
2165static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2166{
2167        unsigned long c;
2168        bool d;
2169        unsigned long flags;
2170        struct rcu_node *rnp = rdp->mynode;
2171
2172        raw_spin_lock_irqsave(&rnp->lock, flags);
2173        c = rcu_start_future_gp(rnp, rdp);
2174        raw_spin_unlock_irqrestore(&rnp->lock, flags);
2175
2176        /*
2177         * Wait for the grace period.  Do so interruptibly to avoid messing
2178         * up the load average.
2179         */
2180        trace_rcu_future_gp(rnp, rdp, c, "StartWait");
2181        for (;;) {
2182                wait_event_interruptible(
2183                        rnp->nocb_gp_wq[c & 0x1],
2184                        (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2185                if (likely(d))
2186                        break;
2187                flush_signals(current);
2188                trace_rcu_future_gp(rnp, rdp, c, "ResumeWait");
2189        }
2190        trace_rcu_future_gp(rnp, rdp, c, "EndWait");
2191        smp_mb(); /* Ensure that CB invocation happens after GP end. */
2192}
2193
2194/*
2195 * Per-rcu_data kthread, but only for no-CBs CPUs.  Each kthread invokes
2196 * callbacks queued by the corresponding no-CBs CPU.
2197 */
2198static int rcu_nocb_kthread(void *arg)
2199{
2200        int c, cl;
2201        struct rcu_head *list;
2202        struct rcu_head *next;
2203        struct rcu_head **tail;
2204        struct rcu_data *rdp = arg;
2205
2206        /* Each pass through this loop invokes one batch of callbacks */
2207        for (;;) {
2208                /* If not polling, wait for next batch of callbacks. */
2209                if (!rcu_nocb_poll)
2210                        wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
2211                list = ACCESS_ONCE(rdp->nocb_head);
2212                if (!list) {
2213                        schedule_timeout_interruptible(1);
2214                        flush_signals(current);
2215                        continue;
2216                }
2217
2218                /*
2219                 * Extract queued callbacks, update counts, and wait
2220                 * for a grace period to elapse.
2221                 */
2222                ACCESS_ONCE(rdp->nocb_head) = NULL;
2223                tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2224                c = atomic_long_xchg(&rdp->nocb_q_count, 0);
2225                cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
2226                ACCESS_ONCE(rdp->nocb_p_count) += c;
2227                ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
2228                rcu_nocb_wait_gp(rdp);
2229
2230                /* Each pass through the following loop invokes a callback. */
2231                trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
2232                c = cl = 0;
2233                while (list) {
2234                        next = list->next;
2235                        /* Wait for enqueuing to complete, if needed. */
2236                        while (next == NULL && &list->next != tail) {
2237                                schedule_timeout_interruptible(1);
2238                                next = list->next;
2239                        }
2240                        debug_rcu_head_unqueue(list);
2241                        local_bh_disable();
2242                        if (__rcu_reclaim(rdp->rsp->name, list))
2243                                cl++;
2244                        c++;
2245                        local_bh_enable();
2246                        list = next;
2247                }
2248                trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2249                ACCESS_ONCE(rdp->nocb_p_count) -= c;
2250                ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
2251                rdp->n_nocbs_invoked += c;
2252        }
2253        return 0;
2254}
2255
2256/* Initialize per-rcu_data variables for no-CBs CPUs. */
2257static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2258{
2259        rdp->nocb_tail = &rdp->nocb_head;
2260        init_waitqueue_head(&rdp->nocb_wq);
2261}
2262
2263/* Create a kthread for each RCU flavor for each no-CBs CPU. */
2264static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2265{
2266        int cpu;
2267        struct rcu_data *rdp;
2268        struct task_struct *t;
2269
2270        if (rcu_nocb_mask == NULL)
2271                return;
2272        for_each_cpu(cpu, rcu_nocb_mask) {
2273                rdp = per_cpu_ptr(rsp->rda, cpu);
2274                t = kthread_run(rcu_nocb_kthread, rdp,
2275                                "rcuo%c/%d", rsp->abbr, cpu);
2276                BUG_ON(IS_ERR(t));
2277                ACCESS_ONCE(rdp->nocb_kthread) = t;
2278        }
2279}
2280
2281/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2282static bool init_nocb_callback_list(struct rcu_data *rdp)
2283{
2284        if (rcu_nocb_mask == NULL ||
2285            !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2286                return false;
2287        rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2288        return true;
2289}
2290
2291#else /* #ifdef CONFIG_RCU_NOCB_CPU */
2292
2293static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2294{
2295        return 0;
2296}
2297
2298static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2299{
2300}
2301
2302static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2303{
2304}
2305
2306static void rcu_init_one_nocb(struct rcu_node *rnp)
2307{
2308}
2309
2310static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2311                            bool lazy)
2312{
2313        return 0;
2314}
2315
2316static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2317                                                     struct rcu_data *rdp)
2318{
2319        return 0;
2320}
2321
2322static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2323{
2324}
2325
2326static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2327{
2328}
2329
2330static bool init_nocb_callback_list(struct rcu_data *rdp)
2331{
2332        return false;
2333}
2334
2335#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2336
2337/*
2338 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2339 * arbitrarily long period of time with the scheduling-clock tick turned
2340 * off.  RCU will be paying attention to this CPU because it is in the
2341 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2342 * machine because the scheduling-clock tick has been disabled.  Therefore,
2343 * if an adaptive-ticks CPU is failing to respond to the current grace
2344 * period and has not be idle from an RCU perspective, kick it.
2345 */
2346static void rcu_kick_nohz_cpu(int cpu)
2347{
2348#ifdef CONFIG_NO_HZ_FULL
2349        if (tick_nohz_full_cpu(cpu))
2350                smp_send_reschedule(cpu);
2351#endif /* #ifdef CONFIG_NO_HZ_FULL */
2352}
2353
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