linux/kernel/rcutiny_plugin.h
<<
>>
Prefs
   1/*
   2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition
   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 (c) 2010 Linaro
  21 *
  22 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  23 */
  24
  25#include <linux/kthread.h>
  26#include <linux/debugfs.h>
  27#include <linux/seq_file.h>
  28
  29#ifdef CONFIG_RCU_TRACE
  30#define RCU_TRACE(stmt) stmt
  31#else /* #ifdef CONFIG_RCU_TRACE */
  32#define RCU_TRACE(stmt)
  33#endif /* #else #ifdef CONFIG_RCU_TRACE */
  34
  35/* Global control variables for rcupdate callback mechanism. */
  36struct rcu_ctrlblk {
  37        struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
  38        struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
  39        struct rcu_head **curtail;      /* ->next pointer of last CB. */
  40        RCU_TRACE(long qlen);           /* Number of pending CBs. */
  41};
  42
  43/* Definition for rcupdate control block. */
  44static struct rcu_ctrlblk rcu_sched_ctrlblk = {
  45        .donetail       = &rcu_sched_ctrlblk.rcucblist,
  46        .curtail        = &rcu_sched_ctrlblk.rcucblist,
  47};
  48
  49static struct rcu_ctrlblk rcu_bh_ctrlblk = {
  50        .donetail       = &rcu_bh_ctrlblk.rcucblist,
  51        .curtail        = &rcu_bh_ctrlblk.rcucblist,
  52};
  53
  54#ifdef CONFIG_DEBUG_LOCK_ALLOC
  55int rcu_scheduler_active __read_mostly;
  56EXPORT_SYMBOL_GPL(rcu_scheduler_active);
  57#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  58
  59#ifdef CONFIG_TINY_PREEMPT_RCU
  60
  61#include <linux/delay.h>
  62
  63/* Global control variables for preemptible RCU. */
  64struct rcu_preempt_ctrlblk {
  65        struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */
  66        struct rcu_head **nexttail;
  67                                /* Tasks blocked in a preemptible RCU */
  68                                /*  read-side critical section while an */
  69                                /*  preemptible-RCU grace period is in */
  70                                /*  progress must wait for a later grace */
  71                                /*  period.  This pointer points to the */
  72                                /*  ->next pointer of the last task that */
  73                                /*  must wait for a later grace period, or */
  74                                /*  to &->rcb.rcucblist if there is no */
  75                                /*  such task. */
  76        struct list_head blkd_tasks;
  77                                /* Tasks blocked in RCU read-side critical */
  78                                /*  section.  Tasks are placed at the head */
  79                                /*  of this list and age towards the tail. */
  80        struct list_head *gp_tasks;
  81                                /* Pointer to the first task blocking the */
  82                                /*  current grace period, or NULL if there */
  83                                /*  is no such task. */
  84        struct list_head *exp_tasks;
  85                                /* Pointer to first task blocking the */
  86                                /*  current expedited grace period, or NULL */
  87                                /*  if there is no such task.  If there */
  88                                /*  is no current expedited grace period, */
  89                                /*  then there cannot be any such task. */
  90#ifdef CONFIG_RCU_BOOST
  91        struct list_head *boost_tasks;
  92                                /* Pointer to first task that needs to be */
  93                                /*  priority-boosted, or NULL if no priority */
  94                                /*  boosting is needed.  If there is no */
  95                                /*  current or expedited grace period, there */
  96                                /*  can be no such task. */
  97#endif /* #ifdef CONFIG_RCU_BOOST */
  98        u8 gpnum;               /* Current grace period. */
  99        u8 gpcpu;               /* Last grace period blocked by the CPU. */
 100        u8 completed;           /* Last grace period completed. */
 101                                /*  If all three are equal, RCU is idle. */
 102#ifdef CONFIG_RCU_BOOST
 103        unsigned long boost_time; /* When to start boosting (jiffies) */
 104#endif /* #ifdef CONFIG_RCU_BOOST */
 105#ifdef CONFIG_RCU_TRACE
 106        unsigned long n_grace_periods;
 107#ifdef CONFIG_RCU_BOOST
 108        unsigned long n_tasks_boosted;
 109                                /* Total number of tasks boosted. */
 110        unsigned long n_exp_boosts;
 111                                /* Number of tasks boosted for expedited GP. */
 112        unsigned long n_normal_boosts;
 113                                /* Number of tasks boosted for normal GP. */
 114        unsigned long n_balk_blkd_tasks;
 115                                /* Refused to boost: no blocked tasks. */
 116        unsigned long n_balk_exp_gp_tasks;
 117                                /* Refused to boost: nothing blocking GP. */
 118        unsigned long n_balk_boost_tasks;
 119                                /* Refused to boost: already boosting. */
 120        unsigned long n_balk_notyet;
 121                                /* Refused to boost: not yet time. */
 122        unsigned long n_balk_nos;
 123                                /* Refused to boost: not sure why, though. */
 124                                /*  This can happen due to race conditions. */
 125#endif /* #ifdef CONFIG_RCU_BOOST */
 126#endif /* #ifdef CONFIG_RCU_TRACE */
 127};
 128
 129static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
 130        .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
 131        .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
 132        .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
 133        .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
 134};
 135
 136static int rcu_preempted_readers_exp(void);
 137static void rcu_report_exp_done(void);
 138
 139/*
 140 * Return true if the CPU has not yet responded to the current grace period.
 141 */
 142static int rcu_cpu_blocking_cur_gp(void)
 143{
 144        return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
 145}
 146
 147/*
 148 * Check for a running RCU reader.  Because there is only one CPU,
 149 * there can be but one running RCU reader at a time.  ;-)
 150 */
 151static int rcu_preempt_running_reader(void)
 152{
 153        return current->rcu_read_lock_nesting;
 154}
 155
 156/*
 157 * Check for preempted RCU readers blocking any grace period.
 158 * If the caller needs a reliable answer, it must disable hard irqs.
 159 */
 160static int rcu_preempt_blocked_readers_any(void)
 161{
 162        return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
 163}
 164
 165/*
 166 * Check for preempted RCU readers blocking the current grace period.
 167 * If the caller needs a reliable answer, it must disable hard irqs.
 168 */
 169static int rcu_preempt_blocked_readers_cgp(void)
 170{
 171        return rcu_preempt_ctrlblk.gp_tasks != NULL;
 172}
 173
 174/*
 175 * Return true if another preemptible-RCU grace period is needed.
 176 */
 177static int rcu_preempt_needs_another_gp(void)
 178{
 179        return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
 180}
 181
 182/*
 183 * Return true if a preemptible-RCU grace period is in progress.
 184 * The caller must disable hardirqs.
 185 */
 186static int rcu_preempt_gp_in_progress(void)
 187{
 188        return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
 189}
 190
 191/*
 192 * Advance a ->blkd_tasks-list pointer to the next entry, instead
 193 * returning NULL if at the end of the list.
 194 */
 195static struct list_head *rcu_next_node_entry(struct task_struct *t)
 196{
 197        struct list_head *np;
 198
 199        np = t->rcu_node_entry.next;
 200        if (np == &rcu_preempt_ctrlblk.blkd_tasks)
 201                np = NULL;
 202        return np;
 203}
 204
 205#ifdef CONFIG_RCU_TRACE
 206
 207#ifdef CONFIG_RCU_BOOST
 208static void rcu_initiate_boost_trace(void);
 209#endif /* #ifdef CONFIG_RCU_BOOST */
 210
 211/*
 212 * Dump additional statistice for TINY_PREEMPT_RCU.
 213 */
 214static void show_tiny_preempt_stats(struct seq_file *m)
 215{
 216        seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
 217                   rcu_preempt_ctrlblk.rcb.qlen,
 218                   rcu_preempt_ctrlblk.n_grace_periods,
 219                   rcu_preempt_ctrlblk.gpnum,
 220                   rcu_preempt_ctrlblk.gpcpu,
 221                   rcu_preempt_ctrlblk.completed,
 222                   "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
 223                   "N."[!rcu_preempt_ctrlblk.gp_tasks],
 224                   "E."[!rcu_preempt_ctrlblk.exp_tasks]);
 225#ifdef CONFIG_RCU_BOOST
 226        seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
 227                   "             ",
 228                   "B."[!rcu_preempt_ctrlblk.boost_tasks],
 229                   rcu_preempt_ctrlblk.n_tasks_boosted,
 230                   rcu_preempt_ctrlblk.n_exp_boosts,
 231                   rcu_preempt_ctrlblk.n_normal_boosts,
 232                   (int)(jiffies & 0xffff),
 233                   (int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
 234        seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n",
 235                   "             balk",
 236                   rcu_preempt_ctrlblk.n_balk_blkd_tasks,
 237                   rcu_preempt_ctrlblk.n_balk_exp_gp_tasks,
 238                   rcu_preempt_ctrlblk.n_balk_boost_tasks,
 239                   rcu_preempt_ctrlblk.n_balk_notyet,
 240                   rcu_preempt_ctrlblk.n_balk_nos);
 241#endif /* #ifdef CONFIG_RCU_BOOST */
 242}
 243
 244#endif /* #ifdef CONFIG_RCU_TRACE */
 245
 246#ifdef CONFIG_RCU_BOOST
 247
 248#include "rtmutex_common.h"
 249
 250/*
 251 * Carry out RCU priority boosting on the task indicated by ->boost_tasks,
 252 * and advance ->boost_tasks to the next task in the ->blkd_tasks list.
 253 */
 254static int rcu_boost(void)
 255{
 256        unsigned long flags;
 257        struct rt_mutex mtx;
 258        struct task_struct *t;
 259        struct list_head *tb;
 260
 261        if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
 262            rcu_preempt_ctrlblk.exp_tasks == NULL)
 263                return 0;  /* Nothing to boost. */
 264
 265        raw_local_irq_save(flags);
 266
 267        /*
 268         * Recheck with irqs disabled: all tasks in need of boosting
 269         * might exit their RCU read-side critical sections on their own
 270         * if we are preempted just before disabling irqs.
 271         */
 272        if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
 273            rcu_preempt_ctrlblk.exp_tasks == NULL) {
 274                raw_local_irq_restore(flags);
 275                return 0;
 276        }
 277
 278        /*
 279         * Preferentially boost tasks blocking expedited grace periods.
 280         * This cannot starve the normal grace periods because a second
 281         * expedited grace period must boost all blocked tasks, including
 282         * those blocking the pre-existing normal grace period.
 283         */
 284        if (rcu_preempt_ctrlblk.exp_tasks != NULL) {
 285                tb = rcu_preempt_ctrlblk.exp_tasks;
 286                RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
 287        } else {
 288                tb = rcu_preempt_ctrlblk.boost_tasks;
 289                RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
 290        }
 291        RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
 292
 293        /*
 294         * We boost task t by manufacturing an rt_mutex that appears to
 295         * be held by task t.  We leave a pointer to that rt_mutex where
 296         * task t can find it, and task t will release the mutex when it
 297         * exits its outermost RCU read-side critical section.  Then
 298         * simply acquiring this artificial rt_mutex will boost task
 299         * t's priority.  (Thanks to tglx for suggesting this approach!)
 300         */
 301        t = container_of(tb, struct task_struct, rcu_node_entry);
 302        rt_mutex_init_proxy_locked(&mtx, t);
 303        t->rcu_boost_mutex = &mtx;
 304        t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
 305        raw_local_irq_restore(flags);
 306        rt_mutex_lock(&mtx);
 307        rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
 308
 309        return rcu_preempt_ctrlblk.boost_tasks != NULL ||
 310               rcu_preempt_ctrlblk.exp_tasks != NULL;
 311}
 312
 313/*
 314 * Check to see if it is now time to start boosting RCU readers blocking
 315 * the current grace period, and, if so, tell the rcu_kthread_task to
 316 * start boosting them.  If there is an expedited boost in progress,
 317 * we wait for it to complete.
 318 *
 319 * If there are no blocked readers blocking the current grace period,
 320 * return 0 to let the caller know, otherwise return 1.  Note that this
 321 * return value is independent of whether or not boosting was done.
 322 */
 323static int rcu_initiate_boost(void)
 324{
 325        if (!rcu_preempt_blocked_readers_cgp() &&
 326            rcu_preempt_ctrlblk.exp_tasks == NULL) {
 327                RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++);
 328                return 0;
 329        }
 330        if (rcu_preempt_ctrlblk.exp_tasks != NULL ||
 331            (rcu_preempt_ctrlblk.gp_tasks != NULL &&
 332             rcu_preempt_ctrlblk.boost_tasks == NULL &&
 333             ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) {
 334                if (rcu_preempt_ctrlblk.exp_tasks == NULL)
 335                        rcu_preempt_ctrlblk.boost_tasks =
 336                                rcu_preempt_ctrlblk.gp_tasks;
 337                invoke_rcu_kthread();
 338        } else
 339                RCU_TRACE(rcu_initiate_boost_trace());
 340        return 1;
 341}
 342
 343#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
 344
 345/*
 346 * Do priority-boost accounting for the start of a new grace period.
 347 */
 348static void rcu_preempt_boost_start_gp(void)
 349{
 350        rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
 351}
 352
 353#else /* #ifdef CONFIG_RCU_BOOST */
 354
 355/*
 356 * If there is no RCU priority boosting, we don't boost.
 357 */
 358static int rcu_boost(void)
 359{
 360        return 0;
 361}
 362
 363/*
 364 * If there is no RCU priority boosting, we don't initiate boosting,
 365 * but we do indicate whether there are blocked readers blocking the
 366 * current grace period.
 367 */
 368static int rcu_initiate_boost(void)
 369{
 370        return rcu_preempt_blocked_readers_cgp();
 371}
 372
 373/*
 374 * If there is no RCU priority boosting, nothing to do at grace-period start.
 375 */
 376static void rcu_preempt_boost_start_gp(void)
 377{
 378}
 379
 380#endif /* else #ifdef CONFIG_RCU_BOOST */
 381
 382/*
 383 * Record a preemptible-RCU quiescent state for the specified CPU.  Note
 384 * that this just means that the task currently running on the CPU is
 385 * in a quiescent state.  There might be any number of tasks blocked
 386 * while in an RCU read-side critical section.
 387 *
 388 * Unlike the other rcu_*_qs() functions, callers to this function
 389 * must disable irqs in order to protect the assignment to
 390 * ->rcu_read_unlock_special.
 391 *
 392 * Because this is a single-CPU implementation, the only way a grace
 393 * period can end is if the CPU is in a quiescent state.  The reason is
 394 * that a blocked preemptible-RCU reader can exit its critical section
 395 * only if the CPU is running it at the time.  Therefore, when the
 396 * last task blocking the current grace period exits its RCU read-side
 397 * critical section, neither the CPU nor blocked tasks will be stopping
 398 * the current grace period.  (In contrast, SMP implementations
 399 * might have CPUs running in RCU read-side critical sections that
 400 * block later grace periods -- but this is not possible given only
 401 * one CPU.)
 402 */
 403static void rcu_preempt_cpu_qs(void)
 404{
 405        /* Record both CPU and task as having responded to current GP. */
 406        rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
 407        current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
 408
 409        /* If there is no GP then there is nothing more to do.  */
 410        if (!rcu_preempt_gp_in_progress())
 411                return;
 412        /*
 413         * Check up on boosting.  If there are readers blocking the
 414         * current grace period, leave.
 415         */
 416        if (rcu_initiate_boost())
 417                return;
 418
 419        /* Advance callbacks. */
 420        rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
 421        rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
 422        rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
 423
 424        /* If there are no blocked readers, next GP is done instantly. */
 425        if (!rcu_preempt_blocked_readers_any())
 426                rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
 427
 428        /* If there are done callbacks, cause them to be invoked. */
 429        if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
 430                invoke_rcu_kthread();
 431}
 432
 433/*
 434 * Start a new RCU grace period if warranted.  Hard irqs must be disabled.
 435 */
 436static void rcu_preempt_start_gp(void)
 437{
 438        if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) {
 439
 440                /* Official start of GP. */
 441                rcu_preempt_ctrlblk.gpnum++;
 442                RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
 443
 444                /* Any blocked RCU readers block new GP. */
 445                if (rcu_preempt_blocked_readers_any())
 446                        rcu_preempt_ctrlblk.gp_tasks =
 447                                rcu_preempt_ctrlblk.blkd_tasks.next;
 448
 449                /* Set up for RCU priority boosting. */
 450                rcu_preempt_boost_start_gp();
 451
 452                /* If there is no running reader, CPU is done with GP. */
 453                if (!rcu_preempt_running_reader())
 454                        rcu_preempt_cpu_qs();
 455        }
 456}
 457
 458/*
 459 * We have entered the scheduler, and the current task might soon be
 460 * context-switched away from.  If this task is in an RCU read-side
 461 * critical section, we will no longer be able to rely on the CPU to
 462 * record that fact, so we enqueue the task on the blkd_tasks list.
 463 * If the task started after the current grace period began, as recorded
 464 * by ->gpcpu, we enqueue at the beginning of the list.  Otherwise
 465 * before the element referenced by ->gp_tasks (or at the tail if
 466 * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element.
 467 * The task will dequeue itself when it exits the outermost enclosing
 468 * RCU read-side critical section.  Therefore, the current grace period
 469 * cannot be permitted to complete until the ->gp_tasks pointer becomes
 470 * NULL.
 471 *
 472 * Caller must disable preemption.
 473 */
 474void rcu_preempt_note_context_switch(void)
 475{
 476        struct task_struct *t = current;
 477        unsigned long flags;
 478
 479        local_irq_save(flags); /* must exclude scheduler_tick(). */
 480        if (rcu_preempt_running_reader() &&
 481            (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 482
 483                /* Possibly blocking in an RCU read-side critical section. */
 484                t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
 485
 486                /*
 487                 * If this CPU has already checked in, then this task
 488                 * will hold up the next grace period rather than the
 489                 * current grace period.  Queue the task accordingly.
 490                 * If the task is queued for the current grace period
 491                 * (i.e., this CPU has not yet passed through a quiescent
 492                 * state for the current grace period), then as long
 493                 * as that task remains queued, the current grace period
 494                 * cannot end.
 495                 */
 496                list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
 497                if (rcu_cpu_blocking_cur_gp())
 498                        rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
 499        }
 500
 501        /*
 502         * Either we were not in an RCU read-side critical section to
 503         * begin with, or we have now recorded that critical section
 504         * globally.  Either way, we can now note a quiescent state
 505         * for this CPU.  Again, if we were in an RCU read-side critical
 506         * section, and if that critical section was blocking the current
 507         * grace period, then the fact that the task has been enqueued
 508         * means that current grace period continues to be blocked.
 509         */
 510        rcu_preempt_cpu_qs();
 511        local_irq_restore(flags);
 512}
 513
 514/*
 515 * Tiny-preemptible RCU implementation for rcu_read_lock().
 516 * Just increment ->rcu_read_lock_nesting, shared state will be updated
 517 * if we block.
 518 */
 519void __rcu_read_lock(void)
 520{
 521        current->rcu_read_lock_nesting++;
 522        barrier();  /* needed if we ever invoke rcu_read_lock in rcutiny.c */
 523}
 524EXPORT_SYMBOL_GPL(__rcu_read_lock);
 525
 526/*
 527 * Handle special cases during rcu_read_unlock(), such as needing to
 528 * notify RCU core processing or task having blocked during the RCU
 529 * read-side critical section.
 530 */
 531static void rcu_read_unlock_special(struct task_struct *t)
 532{
 533        int empty;
 534        int empty_exp;
 535        unsigned long flags;
 536        struct list_head *np;
 537        int special;
 538
 539        /*
 540         * NMI handlers cannot block and cannot safely manipulate state.
 541         * They therefore cannot possibly be special, so just leave.
 542         */
 543        if (in_nmi())
 544                return;
 545
 546        local_irq_save(flags);
 547
 548        /*
 549         * If RCU core is waiting for this CPU to exit critical section,
 550         * let it know that we have done so.
 551         */
 552        special = t->rcu_read_unlock_special;
 553        if (special & RCU_READ_UNLOCK_NEED_QS)
 554                rcu_preempt_cpu_qs();
 555
 556        /* Hardware IRQ handlers cannot block. */
 557        if (in_irq()) {
 558                local_irq_restore(flags);
 559                return;
 560        }
 561
 562        /* Clean up if blocked during RCU read-side critical section. */
 563        if (special & RCU_READ_UNLOCK_BLOCKED) {
 564                t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
 565
 566                /*
 567                 * Remove this task from the ->blkd_tasks list and adjust
 568                 * any pointers that might have been referencing it.
 569                 */
 570                empty = !rcu_preempt_blocked_readers_cgp();
 571                empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
 572                np = rcu_next_node_entry(t);
 573                list_del_init(&t->rcu_node_entry);
 574                if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
 575                        rcu_preempt_ctrlblk.gp_tasks = np;
 576                if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
 577                        rcu_preempt_ctrlblk.exp_tasks = np;
 578#ifdef CONFIG_RCU_BOOST
 579                if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks)
 580                        rcu_preempt_ctrlblk.boost_tasks = np;
 581#endif /* #ifdef CONFIG_RCU_BOOST */
 582
 583                /*
 584                 * If this was the last task on the current list, and if
 585                 * we aren't waiting on the CPU, report the quiescent state
 586                 * and start a new grace period if needed.
 587                 */
 588                if (!empty && !rcu_preempt_blocked_readers_cgp()) {
 589                        rcu_preempt_cpu_qs();
 590                        rcu_preempt_start_gp();
 591                }
 592
 593                /*
 594                 * If this was the last task on the expedited lists,
 595                 * then we need wake up the waiting task.
 596                 */
 597                if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
 598                        rcu_report_exp_done();
 599        }
 600#ifdef CONFIG_RCU_BOOST
 601        /* Unboost self if was boosted. */
 602        if (special & RCU_READ_UNLOCK_BOOSTED) {
 603                t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
 604                rt_mutex_unlock(t->rcu_boost_mutex);
 605                t->rcu_boost_mutex = NULL;
 606        }
 607#endif /* #ifdef CONFIG_RCU_BOOST */
 608        local_irq_restore(flags);
 609}
 610
 611/*
 612 * Tiny-preemptible RCU implementation for rcu_read_unlock().
 613 * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
 614 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
 615 * invoke rcu_read_unlock_special() to clean up after a context switch
 616 * in an RCU read-side critical section and other special cases.
 617 */
 618void __rcu_read_unlock(void)
 619{
 620        struct task_struct *t = current;
 621
 622        barrier();  /* needed if we ever invoke rcu_read_unlock in rcutiny.c */
 623        --t->rcu_read_lock_nesting;
 624        barrier();  /* decrement before load of ->rcu_read_unlock_special */
 625        if (t->rcu_read_lock_nesting == 0 &&
 626            unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
 627                rcu_read_unlock_special(t);
 628#ifdef CONFIG_PROVE_LOCKING
 629        WARN_ON_ONCE(t->rcu_read_lock_nesting < 0);
 630#endif /* #ifdef CONFIG_PROVE_LOCKING */
 631}
 632EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 633
 634/*
 635 * Check for a quiescent state from the current CPU.  When a task blocks,
 636 * the task is recorded in the rcu_preempt_ctrlblk structure, which is
 637 * checked elsewhere.  This is called from the scheduling-clock interrupt.
 638 *
 639 * Caller must disable hard irqs.
 640 */
 641static void rcu_preempt_check_callbacks(void)
 642{
 643        struct task_struct *t = current;
 644
 645        if (rcu_preempt_gp_in_progress() &&
 646            (!rcu_preempt_running_reader() ||
 647             !rcu_cpu_blocking_cur_gp()))
 648                rcu_preempt_cpu_qs();
 649        if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
 650            rcu_preempt_ctrlblk.rcb.donetail)
 651                invoke_rcu_kthread();
 652        if (rcu_preempt_gp_in_progress() &&
 653            rcu_cpu_blocking_cur_gp() &&
 654            rcu_preempt_running_reader())
 655                t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 656}
 657
 658/*
 659 * TINY_PREEMPT_RCU has an extra callback-list tail pointer to
 660 * update, so this is invoked from rcu_process_callbacks() to
 661 * handle that case.  Of course, it is invoked for all flavors of
 662 * RCU, but RCU callbacks can appear only on one of the lists, and
 663 * neither ->nexttail nor ->donetail can possibly be NULL, so there
 664 * is no need for an explicit check.
 665 */
 666static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
 667{
 668        if (rcu_preempt_ctrlblk.nexttail == rcp->donetail)
 669                rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist;
 670}
 671
 672/*
 673 * Process callbacks for preemptible RCU.
 674 */
 675static void rcu_preempt_process_callbacks(void)
 676{
 677        rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
 678}
 679
 680/*
 681 * Queue a preemptible -RCU callback for invocation after a grace period.
 682 */
 683void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 684{
 685        unsigned long flags;
 686
 687        debug_rcu_head_queue(head);
 688        head->func = func;
 689        head->next = NULL;
 690
 691        local_irq_save(flags);
 692        *rcu_preempt_ctrlblk.nexttail = head;
 693        rcu_preempt_ctrlblk.nexttail = &head->next;
 694        RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++);
 695        rcu_preempt_start_gp();  /* checks to see if GP needed. */
 696        local_irq_restore(flags);
 697}
 698EXPORT_SYMBOL_GPL(call_rcu);
 699
 700void rcu_barrier(void)
 701{
 702        struct rcu_synchronize rcu;
 703
 704        init_rcu_head_on_stack(&rcu.head);
 705        init_completion(&rcu.completion);
 706        /* Will wake me after RCU finished. */
 707        call_rcu(&rcu.head, wakeme_after_rcu);
 708        /* Wait for it. */
 709        wait_for_completion(&rcu.completion);
 710        destroy_rcu_head_on_stack(&rcu.head);
 711}
 712EXPORT_SYMBOL_GPL(rcu_barrier);
 713
 714/*
 715 * synchronize_rcu - wait until a grace period has elapsed.
 716 *
 717 * Control will return to the caller some time after a full grace
 718 * period has elapsed, in other words after all currently executing RCU
 719 * read-side critical sections have completed.  RCU read-side critical
 720 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
 721 * and may be nested.
 722 */
 723void synchronize_rcu(void)
 724{
 725#ifdef CONFIG_DEBUG_LOCK_ALLOC
 726        if (!rcu_scheduler_active)
 727                return;
 728#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 729
 730        WARN_ON_ONCE(rcu_preempt_running_reader());
 731        if (!rcu_preempt_blocked_readers_any())
 732                return;
 733
 734        /* Once we get past the fastpath checks, same code as rcu_barrier(). */
 735        rcu_barrier();
 736}
 737EXPORT_SYMBOL_GPL(synchronize_rcu);
 738
 739static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
 740static unsigned long sync_rcu_preempt_exp_count;
 741static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
 742
 743/*
 744 * Return non-zero if there are any tasks in RCU read-side critical
 745 * sections blocking the current preemptible-RCU expedited grace period.
 746 * If there is no preemptible-RCU expedited grace period currently in
 747 * progress, returns zero unconditionally.
 748 */
 749static int rcu_preempted_readers_exp(void)
 750{
 751        return rcu_preempt_ctrlblk.exp_tasks != NULL;
 752}
 753
 754/*
 755 * Report the exit from RCU read-side critical section for the last task
 756 * that queued itself during or before the current expedited preemptible-RCU
 757 * grace period.
 758 */
 759static void rcu_report_exp_done(void)
 760{
 761        wake_up(&sync_rcu_preempt_exp_wq);
 762}
 763
 764/*
 765 * Wait for an rcu-preempt grace period, but expedite it.  The basic idea
 766 * is to rely in the fact that there is but one CPU, and that it is
 767 * illegal for a task to invoke synchronize_rcu_expedited() while in a
 768 * preemptible-RCU read-side critical section.  Therefore, any such
 769 * critical sections must correspond to blocked tasks, which must therefore
 770 * be on the ->blkd_tasks list.  So just record the current head of the
 771 * list in the ->exp_tasks pointer, and wait for all tasks including and
 772 * after the task pointed to by ->exp_tasks to drain.
 773 */
 774void synchronize_rcu_expedited(void)
 775{
 776        unsigned long flags;
 777        struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk;
 778        unsigned long snap;
 779
 780        barrier(); /* ensure prior action seen before grace period. */
 781
 782        WARN_ON_ONCE(rcu_preempt_running_reader());
 783
 784        /*
 785         * Acquire lock so that there is only one preemptible RCU grace
 786         * period in flight.  Of course, if someone does the expedited
 787         * grace period for us while we are acquiring the lock, just leave.
 788         */
 789        snap = sync_rcu_preempt_exp_count + 1;
 790        mutex_lock(&sync_rcu_preempt_exp_mutex);
 791        if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count))
 792                goto unlock_mb_ret; /* Others did our work for us. */
 793
 794        local_irq_save(flags);
 795
 796        /*
 797         * All RCU readers have to already be on blkd_tasks because
 798         * we cannot legally be executing in an RCU read-side critical
 799         * section.
 800         */
 801
 802        /* Snapshot current head of ->blkd_tasks list. */
 803        rpcp->exp_tasks = rpcp->blkd_tasks.next;
 804        if (rpcp->exp_tasks == &rpcp->blkd_tasks)
 805                rpcp->exp_tasks = NULL;
 806
 807        /* Wait for tail of ->blkd_tasks list to drain. */
 808        if (!rcu_preempted_readers_exp())
 809                local_irq_restore(flags);
 810        else {
 811                rcu_initiate_boost();
 812                local_irq_restore(flags);
 813                wait_event(sync_rcu_preempt_exp_wq,
 814                           !rcu_preempted_readers_exp());
 815        }
 816
 817        /* Clean up and exit. */
 818        barrier(); /* ensure expedited GP seen before counter increment. */
 819        sync_rcu_preempt_exp_count++;
 820unlock_mb_ret:
 821        mutex_unlock(&sync_rcu_preempt_exp_mutex);
 822        barrier(); /* ensure subsequent action seen after grace period. */
 823}
 824EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 825
 826/*
 827 * Does preemptible RCU need the CPU to stay out of dynticks mode?
 828 */
 829int rcu_preempt_needs_cpu(void)
 830{
 831        if (!rcu_preempt_running_reader())
 832                rcu_preempt_cpu_qs();
 833        return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
 834}
 835
 836/*
 837 * Check for a task exiting while in a preemptible -RCU read-side
 838 * critical section, clean up if so.  No need to issue warnings,
 839 * as debug_check_no_locks_held() already does this if lockdep
 840 * is enabled.
 841 */
 842void exit_rcu(void)
 843{
 844        struct task_struct *t = current;
 845
 846        if (t->rcu_read_lock_nesting == 0)
 847                return;
 848        t->rcu_read_lock_nesting = 1;
 849        __rcu_read_unlock();
 850}
 851
 852#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
 853
 854#ifdef CONFIG_RCU_TRACE
 855
 856/*
 857 * Because preemptible RCU does not exist, it is not necessary to
 858 * dump out its statistics.
 859 */
 860static void show_tiny_preempt_stats(struct seq_file *m)
 861{
 862}
 863
 864#endif /* #ifdef CONFIG_RCU_TRACE */
 865
 866/*
 867 * Because preemptible RCU does not exist, it is never necessary to
 868 * boost preempted RCU readers.
 869 */
 870static int rcu_boost(void)
 871{
 872        return 0;
 873}
 874
 875/*
 876 * Because preemptible RCU does not exist, it never has any callbacks
 877 * to check.
 878 */
 879static void rcu_preempt_check_callbacks(void)
 880{
 881}
 882
 883/*
 884 * Because preemptible RCU does not exist, it never has any callbacks
 885 * to remove.
 886 */
 887static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
 888{
 889}
 890
 891/*
 892 * Because preemptible RCU does not exist, it never has any callbacks
 893 * to process.
 894 */
 895static void rcu_preempt_process_callbacks(void)
 896{
 897}
 898
 899#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
 900
 901#ifdef CONFIG_DEBUG_LOCK_ALLOC
 902#include <linux/kernel_stat.h>
 903
 904/*
 905 * During boot, we forgive RCU lockdep issues.  After this function is
 906 * invoked, we start taking RCU lockdep issues seriously.
 907 */
 908void __init rcu_scheduler_starting(void)
 909{
 910        WARN_ON(nr_context_switches() > 0);
 911        rcu_scheduler_active = 1;
 912}
 913
 914#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 915
 916#ifdef CONFIG_RCU_BOOST
 917#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
 918#else /* #ifdef CONFIG_RCU_BOOST */
 919#define RCU_BOOST_PRIO 1
 920#endif /* #else #ifdef CONFIG_RCU_BOOST */
 921
 922#ifdef CONFIG_RCU_TRACE
 923
 924#ifdef CONFIG_RCU_BOOST
 925
 926static void rcu_initiate_boost_trace(void)
 927{
 928        if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks))
 929                rcu_preempt_ctrlblk.n_balk_blkd_tasks++;
 930        else if (rcu_preempt_ctrlblk.gp_tasks == NULL &&
 931                 rcu_preempt_ctrlblk.exp_tasks == NULL)
 932                rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++;
 933        else if (rcu_preempt_ctrlblk.boost_tasks != NULL)
 934                rcu_preempt_ctrlblk.n_balk_boost_tasks++;
 935        else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))
 936                rcu_preempt_ctrlblk.n_balk_notyet++;
 937        else
 938                rcu_preempt_ctrlblk.n_balk_nos++;
 939}
 940
 941#endif /* #ifdef CONFIG_RCU_BOOST */
 942
 943static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
 944{
 945        unsigned long flags;
 946
 947        raw_local_irq_save(flags);
 948        rcp->qlen -= n;
 949        raw_local_irq_restore(flags);
 950}
 951
 952/*
 953 * Dump statistics for TINY_RCU, such as they are.
 954 */
 955static int show_tiny_stats(struct seq_file *m, void *unused)
 956{
 957        show_tiny_preempt_stats(m);
 958        seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
 959        seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
 960        return 0;
 961}
 962
 963static int show_tiny_stats_open(struct inode *inode, struct file *file)
 964{
 965        return single_open(file, show_tiny_stats, NULL);
 966}
 967
 968static const struct file_operations show_tiny_stats_fops = {
 969        .owner = THIS_MODULE,
 970        .open = show_tiny_stats_open,
 971        .read = seq_read,
 972        .llseek = seq_lseek,
 973        .release = single_release,
 974};
 975
 976static struct dentry *rcudir;
 977
 978static int __init rcutiny_trace_init(void)
 979{
 980        struct dentry *retval;
 981
 982        rcudir = debugfs_create_dir("rcu", NULL);
 983        if (!rcudir)
 984                goto free_out;
 985        retval = debugfs_create_file("rcudata", 0444, rcudir,
 986                                     NULL, &show_tiny_stats_fops);
 987        if (!retval)
 988                goto free_out;
 989        return 0;
 990free_out:
 991        debugfs_remove_recursive(rcudir);
 992        return 1;
 993}
 994
 995static void __exit rcutiny_trace_cleanup(void)
 996{
 997        debugfs_remove_recursive(rcudir);
 998}
 999
1000module_init(rcutiny_trace_init);
1001module_exit(rcutiny_trace_cleanup);
1002
1003MODULE_AUTHOR("Paul E. McKenney");
1004MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
1005MODULE_LICENSE("GPL");
1006
1007#endif /* #ifdef CONFIG_RCU_TRACE */
1008
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.