sys/kern/subr_taskqueue.c

   1 /*-
   2  * Copyright (c) 2000 Doug Rabson
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  */
  26
  27 #include <sys/cdefs.h>
  28 __FBSDID("$FreeBSD$");
  29
  30 #include <sys/param.h>
  31 #include <sys/systm.h>
  32 #include <sys/bus.h>
  33 #include <sys/interrupt.h>
  34 #include <sys/kernel.h>
  35 #include <sys/kthread.h>
  36 #include <sys/limits.h>
  37 #include <sys/lock.h>
  38 #include <sys/malloc.h>
  39 #include <sys/mutex.h>
  40 #include <sys/proc.h>
  41 #include <sys/sched.h>
  42 #include <sys/taskqueue.h>
  43 #include <sys/unistd.h>
  44 #include <machine/stdarg.h>
  45
  46 static MALLOC_DEFINE(M_TASKQUEUE, "taskqueue", "Task Queues");
  47 static void     *taskqueue_giant_ih;
  48 static void     *taskqueue_ih;
  49
  50 struct taskqueue_busy {
  51         struct task     *tb_running;
  52         TAILQ_ENTRY(taskqueue_busy) tb_link;
  53 };
  54
  55 struct taskqueue {
  56         STAILQ_HEAD(, task)     tq_queue;
  57         taskqueue_enqueue_fn    tq_enqueue;
  58         void                    *tq_context;
  59         TAILQ_HEAD(, taskqueue_busy) tq_active;
  60         struct mtx              tq_mutex;
  61         struct thread           **tq_threads;
  62         int                     tq_tcount;
  63         int                     tq_spin;
  64         int                     tq_flags;
  65         int                     tq_callouts;
  66 };
  67
  68 #define TQ_FLAGS_ACTIVE         (1 << 0)
  69 #define TQ_FLAGS_BLOCKED        (1 << 1)
  70 #define TQ_FLAGS_PENDING        (1 << 2)
  71
  72 #define DT_CALLOUT_ARMED        (1 << 0)
  73 #define DT_DRAIN_IN_PROGRESS    (1 << 1)
  74
  75 #define TQ_LOCK(tq)                                                     \
  76         do {                                                            \
  77                 if ((tq)->tq_spin)                                      \
  78                         mtx_lock_spin(&(tq)->tq_mutex);                 \
  79                 else                                                    \
  80                         mtx_lock(&(tq)->tq_mutex);                      \
  81         } while (0)
  82
  83 #define TQ_UNLOCK(tq)                                                   \
  84         do {                                                            \
  85                 if ((tq)->tq_spin)                                      \
  86                         mtx_unlock_spin(&(tq)->tq_mutex);               \
  87                 else                                                    \
  88                         mtx_unlock(&(tq)->tq_mutex);                    \
  89         } while (0)
  90
  91 void
  92 _timeout_task_init(struct taskqueue *queue, struct timeout_task *timeout_task,
  93     int priority, task_fn_t func, void *context)
  94 {
  95
  96         TASK_INIT(&timeout_task->t, priority, func, context);
  97         callout_init_mtx(&timeout_task->c, &queue->tq_mutex, 0);
  98         timeout_task->q = queue;
  99         timeout_task->f = 0;
 100 }
 101
 102 static __inline int
 103 TQ_SLEEP(struct taskqueue *tq, void *p, struct mtx *m, int pri, const char *wm,
 104     int t)
 105 {
 106         if (tq->tq_spin)
 107                 return (msleep_spin(p, m, wm, t));
 108         return (msleep(p, m, pri, wm, t));
 109 }
 110
 111 static struct taskqueue *
 112 _taskqueue_create(const char *name __unused, int mflags,
 113                  taskqueue_enqueue_fn enqueue, void *context,
 114                  int mtxflags, const char *mtxname)
 115 {
 116         struct taskqueue *queue;
 117
 118         queue = malloc(sizeof(struct taskqueue), M_TASKQUEUE, mflags | M_ZERO);
 119         if (!queue)
 120                 return NULL;
 121
 122         STAILQ_INIT(&queue->tq_queue);
 123         TAILQ_INIT(&queue->tq_active);
 124         queue->tq_enqueue = enqueue;
 125         queue->tq_context = context;
 126         queue->tq_spin = (mtxflags & MTX_SPIN) != 0;
 127         queue->tq_flags |= TQ_FLAGS_ACTIVE;
 128         mtx_init(&queue->tq_mutex, mtxname, NULL, mtxflags);
 129
 130         return queue;
 131 }
 132
 133 struct taskqueue *
 134 taskqueue_create(const char *name, int mflags,
 135                  taskqueue_enqueue_fn enqueue, void *context)
 136 {
 137         return _taskqueue_create(name, mflags, enqueue, context,
 138                         MTX_DEF, "taskqueue");
 139 }
 140
 141 /*
 142  * Signal a taskqueue thread to terminate.
 143  */
 144 static void
 145 taskqueue_terminate(struct thread **pp, struct taskqueue *tq)
 146 {
 147
 148         while (tq->tq_tcount > 0 || tq->tq_callouts > 0) {
 149                 wakeup(tq);
 150                 TQ_SLEEP(tq, pp, &tq->tq_mutex, PWAIT, "taskqueue_destroy", 0);
 151         }
 152 }
 153
 154 void
 155 taskqueue_free(struct taskqueue *queue)
 156 {
 157
 158         TQ_LOCK(queue);
 159         queue->tq_flags &= ~TQ_FLAGS_ACTIVE;
 160         taskqueue_terminate(queue->tq_threads, queue);
 161         KASSERT(TAILQ_EMPTY(&queue->tq_active), ("Tasks still running?"));
 162         KASSERT(queue->tq_callouts == 0, ("Armed timeout tasks"));
 163         mtx_destroy(&queue->tq_mutex);
 164         free(queue->tq_threads, M_TASKQUEUE);
 165         free(queue, M_TASKQUEUE);
 166 }
 167
 168 static int
 169 taskqueue_enqueue_locked(struct taskqueue *queue, struct task *task)
 170 {
 171         struct task *ins;
 172         struct task *prev;
 173
 174         /*
 175          * Count multiple enqueues.
 176          */
 177         if (task->ta_pending) {
 178                 if (task->ta_pending < USHRT_MAX)
 179                         task->ta_pending++;
 180                 return (0);
 181         }
 182
 183         /*
 184          * Optimise the case when all tasks have the same priority.
 185          */
 186         prev = STAILQ_LAST(&queue->tq_queue, task, ta_link);
 187         if (!prev || prev->ta_priority >= task->ta_priority) {
 188                 STAILQ_INSERT_TAIL(&queue->tq_queue, task, ta_link);
 189         } else {
 190                 prev = NULL;
 191                 for (ins = STAILQ_FIRST(&queue->tq_queue); ins;
 192                      prev = ins, ins = STAILQ_NEXT(ins, ta_link))
 193                         if (ins->ta_priority < task->ta_priority)
 194                                 break;
 195
 196                 if (prev)
 197                         STAILQ_INSERT_AFTER(&queue->tq_queue, prev, task, ta_link);
 198                 else
 199                         STAILQ_INSERT_HEAD(&queue->tq_queue, task, ta_link);
 200         }
 201
 202         task->ta_pending = 1;
 203         if ((queue->tq_flags & TQ_FLAGS_BLOCKED) == 0)
 204                 queue->tq_enqueue(queue->tq_context);
 205         else
 206                 queue->tq_flags |= TQ_FLAGS_PENDING;
 207
 208         return (0);
 209 }
 210 int
 211 taskqueue_enqueue(struct taskqueue *queue, struct task *task)
 212 {
 213         int res;
 214
 215         TQ_LOCK(queue);
 216         res = taskqueue_enqueue_locked(queue, task);
 217         TQ_UNLOCK(queue);
 218
 219         return (res);
 220 }
 221
 222 static void
 223 taskqueue_timeout_func(void *arg)
 224 {
 225         struct taskqueue *queue;
 226         struct timeout_task *timeout_task;
 227
 228         timeout_task = arg;
 229         queue = timeout_task->q;
 230         KASSERT((timeout_task->f & DT_CALLOUT_ARMED) != 0, ("Stray timeout"));
 231         timeout_task->f &= ~DT_CALLOUT_ARMED;
 232         queue->tq_callouts--;
 233         taskqueue_enqueue_locked(timeout_task->q, &timeout_task->t);
 234 }
 235
 236 int
 237 taskqueue_enqueue_timeout(struct taskqueue *queue,
 238     struct timeout_task *timeout_task, int ticks)
 239 {
 240         int res;
 241
 242         TQ_LOCK(queue);
 243         KASSERT(timeout_task->q == NULL || timeout_task->q == queue,
 244             ("Migrated queue"));
 245         KASSERT(!queue->tq_spin, ("Timeout for spin-queue"));
 246         timeout_task->q = queue;
 247         res = timeout_task->t.ta_pending;
 248         if (timeout_task->f & DT_DRAIN_IN_PROGRESS) {
 249                 /* Do nothing */
 250                 TQ_UNLOCK(queue);
 251                 res = -1;
 252         } else if (ticks == 0) {
 253                 taskqueue_enqueue_locked(queue, &timeout_task->t);
 254         } else {
 255                 if ((timeout_task->f & DT_CALLOUT_ARMED) != 0) {
 256                         res++;
 257                 } else {
 258                         queue->tq_callouts++;
 259                         timeout_task->f |= DT_CALLOUT_ARMED;
 260                         if (ticks < 0)
 261                                 ticks = -ticks; /* Ignore overflow. */
 262                 }
 263                 if (ticks > 0) {
 264                         callout_reset(&timeout_task->c, ticks,
 265                             taskqueue_timeout_func, timeout_task);
 266                 }
 267         }
 268         TQ_UNLOCK(queue);
 269         return (res);
 270 }
 271
 272 static void
 273 taskqueue_drain_running(struct taskqueue *queue)
 274 {
 275
 276         while (!TAILQ_EMPTY(&queue->tq_active))
 277                 TQ_SLEEP(queue, &queue->tq_active, &queue->tq_mutex,
 278                     PWAIT, "-", 0);
 279 }
 280
 281 void
 282 taskqueue_block(struct taskqueue *queue)
 283 {
 284
 285         TQ_LOCK(queue);
 286         queue->tq_flags |= TQ_FLAGS_BLOCKED;
 287         TQ_UNLOCK(queue);
 288 }
 289
 290 void
 291 taskqueue_unblock(struct taskqueue *queue)
 292 {
 293
 294         TQ_LOCK(queue);
 295         queue->tq_flags &= ~TQ_FLAGS_BLOCKED;
 296         if (queue->tq_flags & TQ_FLAGS_PENDING) {
 297                 queue->tq_flags &= ~TQ_FLAGS_PENDING;
 298                 queue->tq_enqueue(queue->tq_context);
 299         }
 300         TQ_UNLOCK(queue);
 301 }
 302
 303 static void
 304 taskqueue_run_locked(struct taskqueue *queue)
 305 {
 306         struct taskqueue_busy tb;
 307         struct task *task;
 308         int pending;
 309
 310         mtx_assert(&queue->tq_mutex, MA_OWNED);
 311         tb.tb_running = NULL;
 312         TAILQ_INSERT_TAIL(&queue->tq_active, &tb, tb_link);
 313
 314         while (STAILQ_FIRST(&queue->tq_queue)) {
 315                 /*
 316                  * Carefully remove the first task from the queue and
 317                  * zero its pending count.
 318                  */
 319                 task = STAILQ_FIRST(&queue->tq_queue);
 320                 STAILQ_REMOVE_HEAD(&queue->tq_queue, ta_link);
 321                 pending = task->ta_pending;
 322                 task->ta_pending = 0;
 323                 tb.tb_running = task;
 324                 TQ_UNLOCK(queue);
 325
 326                 task->ta_func(task->ta_context, pending);
 327
 328                 TQ_LOCK(queue);
 329                 tb.tb_running = NULL;
 330                 wakeup(task);
 331         }
 332         TAILQ_REMOVE(&queue->tq_active, &tb, tb_link);
 333         if (TAILQ_EMPTY(&queue->tq_active))
 334                 wakeup(&queue->tq_active);
 335 }
 336
 337 void
 338 taskqueue_run(struct taskqueue *queue)
 339 {
 340
 341         TQ_LOCK(queue);
 342         taskqueue_run_locked(queue);
 343         TQ_UNLOCK(queue);
 344 }
 345
 346 static int
 347 task_is_running(struct taskqueue *queue, struct task *task)
 348 {
 349         struct taskqueue_busy *tb;
 350
 351         mtx_assert(&queue->tq_mutex, MA_OWNED);
 352         TAILQ_FOREACH(tb, &queue->tq_active, tb_link) {
 353                 if (tb->tb_running == task)
 354                         return (1);
 355         }
 356         return (0);
 357 }
 358
 359 /*
 360  * Only use this function in single threaded contexts. It returns
 361  * non-zero if the given task is either pending or running. Else the
 362  * task is idle and can be queued again or freed.
 363  */
 364 int
 365 taskqueue_poll_is_busy(struct taskqueue *queue, struct task *task)
 366 {
 367         int retval;
 368
 369         TQ_LOCK(queue);
 370         retval = task->ta_pending > 0 || task_is_running(queue, task);
 371         TQ_UNLOCK(queue);
 372
 373         return (retval);
 374 }
 375
 376 static int
 377 taskqueue_cancel_locked(struct taskqueue *queue, struct task *task,
 378     u_int *pendp)
 379 {
 380
 381         if (task->ta_pending > 0)
 382                 STAILQ_REMOVE(&queue->tq_queue, task, task, ta_link);
 383         if (pendp != NULL)
 384                 *pendp = task->ta_pending;
 385         task->ta_pending = 0;
 386         return (task_is_running(queue, task) ? EBUSY : 0);
 387 }
 388
 389 int
 390 taskqueue_cancel(struct taskqueue *queue, struct task *task, u_int *pendp)
 391 {
 392         int error;
 393
 394         TQ_LOCK(queue);
 395         error = taskqueue_cancel_locked(queue, task, pendp);
 396         TQ_UNLOCK(queue);
 397
 398         return (error);
 399 }
 400
 401 int
 402 taskqueue_cancel_timeout(struct taskqueue *queue,
 403     struct timeout_task *timeout_task, u_int *pendp)
 404 {
 405         u_int pending, pending1;
 406         int error;
 407
 408         TQ_LOCK(queue);
 409         pending = !!callout_stop(&timeout_task->c);
 410         error = taskqueue_cancel_locked(queue, &timeout_task->t, &pending1);
 411         if ((timeout_task->f & DT_CALLOUT_ARMED) != 0) {
 412                 timeout_task->f &= ~DT_CALLOUT_ARMED;
 413                 queue->tq_callouts--;
 414         }
 415         TQ_UNLOCK(queue);
 416
 417         if (pendp != NULL)
 418                 *pendp = pending + pending1;
 419         return (error);
 420 }
 421
 422 void
 423 taskqueue_drain(struct taskqueue *queue, struct task *task)
 424 {
 425
 426         if (!queue->tq_spin)
 427                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
 428
 429         TQ_LOCK(queue);
 430         while (task->ta_pending != 0 || task_is_running(queue, task))
 431                 TQ_SLEEP(queue, task, &queue->tq_mutex, PWAIT, "-", 0);
 432         TQ_UNLOCK(queue);
 433 }
 434
 435 void
 436 taskqueue_drain_all(struct taskqueue *queue)
 437 {
 438         struct task *task;
 439
 440         if (!queue->tq_spin)
 441                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
 442
 443         TQ_LOCK(queue);
 444         task = STAILQ_LAST(&queue->tq_queue, task, ta_link);
 445         if (task != NULL)
 446                 while (task->ta_pending != 0)
 447                         TQ_SLEEP(queue, task, &queue->tq_mutex, PWAIT, "-", 0);
 448         taskqueue_drain_running(queue);
 449         KASSERT(STAILQ_EMPTY(&queue->tq_queue),
 450             ("taskqueue queue is not empty after draining"));
 451         TQ_UNLOCK(queue);
 452 }
 453
 454 void
 455 taskqueue_drain_timeout(struct taskqueue *queue,
 456     struct timeout_task *timeout_task)
 457 {
 458
 459         /*
 460          * Set flag to prevent timer from re-starting during drain:
 461          */
 462         TQ_LOCK(queue);
 463         KASSERT((timeout_task->f & DT_DRAIN_IN_PROGRESS) == 0,
 464             ("Drain already in progress"));
 465         timeout_task->f |= DT_DRAIN_IN_PROGRESS;
 466         TQ_UNLOCK(queue);
 467
 468         callout_drain(&timeout_task->c);
 469         taskqueue_drain(queue, &timeout_task->t);
 470
 471         /*
 472          * Clear flag to allow timer to re-start:
 473          */
 474         TQ_LOCK(queue);
 475         timeout_task->f &= ~DT_DRAIN_IN_PROGRESS;
 476         TQ_UNLOCK(queue);
 477 }
 478
 479 static void
 480 taskqueue_swi_enqueue(void *context)
 481 {
 482         swi_sched(taskqueue_ih, 0);
 483 }
 484
 485 static void
 486 taskqueue_swi_run(void *dummy)
 487 {
 488         taskqueue_run(taskqueue_swi);
 489 }
 490
 491 static void
 492 taskqueue_swi_giant_enqueue(void *context)
 493 {
 494         swi_sched(taskqueue_giant_ih, 0);
 495 }
 496
 497 static void
 498 taskqueue_swi_giant_run(void *dummy)
 499 {
 500         taskqueue_run(taskqueue_swi_giant);
 501 }
 502
 503 int
 504 taskqueue_start_threads(struct taskqueue **tqp, int count, int pri,
 505                         const char *name, ...)
 506 {
 507         va_list ap;
 508         struct thread *td;
 509         struct taskqueue *tq;
 510         int i, error;
 511         char ktname[MAXCOMLEN + 1];
 512
 513         if (count <= 0)
 514                 return (EINVAL);
 515
 516         tq = *tqp;
 517
 518         va_start(ap, name);
 519         vsnprintf(ktname, sizeof(ktname), name, ap);
 520         va_end(ap);
 521
 522         tq->tq_threads = malloc(sizeof(struct thread *) * count, M_TASKQUEUE,
 523             M_NOWAIT | M_ZERO);
 524         if (tq->tq_threads == NULL) {
 525                 printf("%s: no memory for %s threads\n", __func__, ktname);
 526                 return (ENOMEM);
 527         }
 528
 529         for (i = 0; i < count; i++) {
 530                 if (count == 1)
 531                         error = kthread_add(taskqueue_thread_loop, tqp, NULL,
 532                             &tq->tq_threads[i], RFSTOPPED, 0, "%s", ktname);
 533                 else
 534                         error = kthread_add(taskqueue_thread_loop, tqp, NULL,
 535                             &tq->tq_threads[i], RFSTOPPED, 0,
 536                             "%s_%d", ktname, i);
 537                 if (error) {
 538                         /* should be ok to continue, taskqueue_free will dtrt */
 539                         printf("%s: kthread_add(%s): error %d", __func__,
 540                             ktname, error);
 541                         tq->tq_threads[i] = NULL;               /* paranoid */
 542                 } else
 543                         tq->tq_tcount++;
 544         }
 545         for (i = 0; i < count; i++) {
 546                 if (tq->tq_threads[i] == NULL)
 547                         continue;
 548                 td = tq->tq_threads[i];
 549                 thread_lock(td);
 550                 sched_prio(td, pri);
 551                 sched_add(td, SRQ_BORING);
 552                 thread_unlock(td);
 553         }
 554
 555         return (0);
 556 }
 557
 558 void
 559 taskqueue_thread_loop(void *arg)
 560 {
 561         struct taskqueue **tqp, *tq;
 562
 563         tqp = arg;
 564         tq = *tqp;
 565         TQ_LOCK(tq);
 566         while ((tq->tq_flags & TQ_FLAGS_ACTIVE) != 0) {
 567                 taskqueue_run_locked(tq);
 568                 /*
 569                  * Because taskqueue_run() can drop tq_mutex, we need to
 570                  * check if the TQ_FLAGS_ACTIVE flag wasn't removed in the
 571                  * meantime, which means we missed a wakeup.
 572                  */
 573                 if ((tq->tq_flags & TQ_FLAGS_ACTIVE) == 0)
 574                         break;
 575                 TQ_SLEEP(tq, tq, &tq->tq_mutex, 0, "-", 0);
 576         }
 577         taskqueue_run_locked(tq);
 578
 579         /* rendezvous with thread that asked us to terminate */
 580         tq->tq_tcount--;
 581         wakeup_one(tq->tq_threads);
 582         TQ_UNLOCK(tq);
 583         kthread_exit();
 584 }
 585
 586 void
 587 taskqueue_thread_enqueue(void *context)
 588 {
 589         struct taskqueue **tqp, *tq;
 590
 591         tqp = context;
 592         tq = *tqp;
 593
 594         mtx_assert(&tq->tq_mutex, MA_OWNED);
 595         wakeup_one(tq);
 596 }
 597
 598 TASKQUEUE_DEFINE(swi, taskqueue_swi_enqueue, NULL,
 599                  swi_add(NULL, "task queue", taskqueue_swi_run, NULL, SWI_TQ,
 600                      INTR_MPSAFE, &taskqueue_ih));
 601
 602 TASKQUEUE_DEFINE(swi_giant, taskqueue_swi_giant_enqueue, NULL,
 603                  swi_add(NULL, "Giant taskq", taskqueue_swi_giant_run,
 604                      NULL, SWI_TQ_GIANT, 0, &taskqueue_giant_ih));
 605
 606 TASKQUEUE_DEFINE_THREAD(thread);
 607
 608 struct taskqueue *
 609 taskqueue_create_fast(const char *name, int mflags,
 610                  taskqueue_enqueue_fn enqueue, void *context)
 611 {
 612         return _taskqueue_create(name, mflags, enqueue, context,
 613                         MTX_SPIN, "fast_taskqueue");
 614 }
 615
 616 /* NB: for backwards compatibility */
 617 int
 618 taskqueue_enqueue_fast(struct taskqueue *queue, struct task *task)
 619 {
 620         return taskqueue_enqueue(queue, task);
 621 }
 622
 623 static void     *taskqueue_fast_ih;
 624
 625 static void
 626 taskqueue_fast_enqueue(void *context)
 627 {
 628         swi_sched(taskqueue_fast_ih, 0);
 629 }
 630
 631 static void
 632 taskqueue_fast_run(void *dummy)
 633 {
 634         taskqueue_run(taskqueue_fast);
 635 }
 636
 637 TASKQUEUE_FAST_DEFINE(fast, taskqueue_fast_enqueue, NULL,
 638         swi_add(NULL, "fast taskq", taskqueue_fast_run, NULL,
 639         SWI_TQ_FAST, INTR_MPSAFE, &taskqueue_fast_ih));
 640
 641 int
 642 taskqueue_member(struct taskqueue *queue, struct thread *td)
 643 {
 644         int i, j, ret = 0;
 645
 646         for (i = 0, j = 0; ; i++) {
 647                 if (queue->tq_threads[i] == NULL)
 648                         continue;
 649                 if (queue->tq_threads[i] == td) {
 650                         ret = 1;
 651                         break;
 652                 }
 653                 if (++j >= queue->tq_tcount)
 654                         break;
 655         }
 656         return (ret);
 657 }