The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_sleepqueue.c

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    1 /*-
    2  * Copyright (c) 2004 John Baldwin <jhb@FreeBSD.org>
    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 /*
   28  * Implementation of sleep queues used to hold queue of threads blocked on
   29  * a wait channel.  Sleep queues different from turnstiles in that wait
   30  * channels are not owned by anyone, so there is no priority propagation.
   31  * Sleep queues can also provide a timeout and can also be interrupted by
   32  * signals.  That said, there are several similarities between the turnstile
   33  * and sleep queue implementations.  (Note: turnstiles were implemented
   34  * first.)  For example, both use a hash table of the same size where each
   35  * bucket is referred to as a "chain" that contains both a spin lock and
   36  * a linked list of queues.  An individual queue is located by using a hash
   37  * to pick a chain, locking the chain, and then walking the chain searching
   38  * for the queue.  This means that a wait channel object does not need to
   39  * embed it's queue head just as locks do not embed their turnstile queue
   40  * head.  Threads also carry around a sleep queue that they lend to the
   41  * wait channel when blocking.  Just as in turnstiles, the queue includes
   42  * a free list of the sleep queues of other threads blocked on the same
   43  * wait channel in the case of multiple waiters.
   44  *
   45  * Some additional functionality provided by sleep queues include the
   46  * ability to set a timeout.  The timeout is managed using a per-thread
   47  * callout that resumes a thread if it is asleep.  A thread may also
   48  * catch signals while it is asleep (aka an interruptible sleep).  The
   49  * signal code uses sleepq_abort() to interrupt a sleeping thread.  Finally,
   50  * sleep queues also provide some extra assertions.  One is not allowed to
   51  * mix the sleep/wakeup and cv APIs for a given wait channel.  Also, one
   52  * must consistently use the same lock to synchronize with a wait channel,
   53  * though this check is currently only a warning for sleep/wakeup due to
   54  * pre-existing abuse of that API.  The same lock must also be held when
   55  * awakening threads, though that is currently only enforced for condition
   56  * variables.
   57  */
   58 
   59 #include <sys/cdefs.h>
   60 __FBSDID("$FreeBSD: releng/10.2/sys/kern/subr_sleepqueue.c 262192 2014-02-18 20:27:17Z jhb $");
   61 
   62 #include "opt_sleepqueue_profiling.h"
   63 #include "opt_ddb.h"
   64 #include "opt_kdtrace.h"
   65 #include "opt_sched.h"
   66 
   67 #include <sys/param.h>
   68 #include <sys/systm.h>
   69 #include <sys/lock.h>
   70 #include <sys/kernel.h>
   71 #include <sys/ktr.h>
   72 #include <sys/mutex.h>
   73 #include <sys/proc.h>
   74 #include <sys/sbuf.h>
   75 #include <sys/sched.h>
   76 #include <sys/sdt.h>
   77 #include <sys/signalvar.h>
   78 #include <sys/sleepqueue.h>
   79 #include <sys/sysctl.h>
   80 
   81 #include <vm/uma.h>
   82 
   83 #ifdef DDB
   84 #include <ddb/ddb.h>
   85 #endif
   86 
   87 /*
   88  * Constants for the hash table of sleep queue chains.
   89  * SC_TABLESIZE must be a power of two for SC_MASK to work properly.
   90  */
   91 #define SC_TABLESIZE    256                     /* Must be power of 2. */
   92 #define SC_MASK         (SC_TABLESIZE - 1)
   93 #define SC_SHIFT        8
   94 #define SC_HASH(wc)     ((((uintptr_t)(wc) >> SC_SHIFT) ^ (uintptr_t)(wc)) & \
   95                             SC_MASK)
   96 #define SC_LOOKUP(wc)   &sleepq_chains[SC_HASH(wc)]
   97 #define NR_SLEEPQS      2
   98 /*
   99  * There two different lists of sleep queues.  Both lists are connected
  100  * via the sq_hash entries.  The first list is the sleep queue chain list
  101  * that a sleep queue is on when it is attached to a wait channel.  The
  102  * second list is the free list hung off of a sleep queue that is attached
  103  * to a wait channel.
  104  *
  105  * Each sleep queue also contains the wait channel it is attached to, the
  106  * list of threads blocked on that wait channel, flags specific to the
  107  * wait channel, and the lock used to synchronize with a wait channel.
  108  * The flags are used to catch mismatches between the various consumers
  109  * of the sleep queue API (e.g. sleep/wakeup and condition variables).
  110  * The lock pointer is only used when invariants are enabled for various
  111  * debugging checks.
  112  *
  113  * Locking key:
  114  *  c - sleep queue chain lock
  115  */
  116 struct sleepqueue {
  117         TAILQ_HEAD(, thread) sq_blocked[NR_SLEEPQS];    /* (c) Blocked threads. */
  118         u_int sq_blockedcnt[NR_SLEEPQS];        /* (c) N. of blocked threads. */
  119         LIST_ENTRY(sleepqueue) sq_hash;         /* (c) Chain and free list. */
  120         LIST_HEAD(, sleepqueue) sq_free;        /* (c) Free queues. */
  121         void    *sq_wchan;                      /* (c) Wait channel. */
  122         int     sq_type;                        /* (c) Queue type. */
  123 #ifdef INVARIANTS
  124         struct lock_object *sq_lock;            /* (c) Associated lock. */
  125 #endif
  126 };
  127 
  128 struct sleepqueue_chain {
  129         LIST_HEAD(, sleepqueue) sc_queues;      /* List of sleep queues. */
  130         struct mtx sc_lock;                     /* Spin lock for this chain. */
  131 #ifdef SLEEPQUEUE_PROFILING
  132         u_int   sc_depth;                       /* Length of sc_queues. */
  133         u_int   sc_max_depth;                   /* Max length of sc_queues. */
  134 #endif
  135 };
  136 
  137 #ifdef SLEEPQUEUE_PROFILING
  138 u_int sleepq_max_depth;
  139 static SYSCTL_NODE(_debug, OID_AUTO, sleepq, CTLFLAG_RD, 0, "sleepq profiling");
  140 static SYSCTL_NODE(_debug_sleepq, OID_AUTO, chains, CTLFLAG_RD, 0,
  141     "sleepq chain stats");
  142 SYSCTL_UINT(_debug_sleepq, OID_AUTO, max_depth, CTLFLAG_RD, &sleepq_max_depth,
  143     0, "maxmimum depth achieved of a single chain");
  144 
  145 static void     sleepq_profile(const char *wmesg);
  146 static int      prof_enabled;
  147 #endif
  148 static struct sleepqueue_chain sleepq_chains[SC_TABLESIZE];
  149 static uma_zone_t sleepq_zone;
  150 
  151 /*
  152  * Prototypes for non-exported routines.
  153  */
  154 static int      sleepq_catch_signals(void *wchan, int pri);
  155 static int      sleepq_check_signals(void);
  156 static int      sleepq_check_timeout(void);
  157 #ifdef INVARIANTS
  158 static void     sleepq_dtor(void *mem, int size, void *arg);
  159 #endif
  160 static int      sleepq_init(void *mem, int size, int flags);
  161 static int      sleepq_resume_thread(struct sleepqueue *sq, struct thread *td,
  162                     int pri);
  163 static void     sleepq_switch(void *wchan, int pri);
  164 static void     sleepq_timeout(void *arg);
  165 
  166 SDT_PROBE_DECLARE(sched, , , sleep);
  167 SDT_PROBE_DECLARE(sched, , , wakeup);
  168 
  169 /*
  170  * Early initialization of sleep queues that is called from the sleepinit()
  171  * SYSINIT.
  172  */
  173 void
  174 init_sleepqueues(void)
  175 {
  176 #ifdef SLEEPQUEUE_PROFILING
  177         struct sysctl_oid *chain_oid;
  178         char chain_name[10];
  179 #endif
  180         int i;
  181 
  182         for (i = 0; i < SC_TABLESIZE; i++) {
  183                 LIST_INIT(&sleepq_chains[i].sc_queues);
  184                 mtx_init(&sleepq_chains[i].sc_lock, "sleepq chain", NULL,
  185                     MTX_SPIN | MTX_RECURSE);
  186 #ifdef SLEEPQUEUE_PROFILING
  187                 snprintf(chain_name, sizeof(chain_name), "%d", i);
  188                 chain_oid = SYSCTL_ADD_NODE(NULL, 
  189                     SYSCTL_STATIC_CHILDREN(_debug_sleepq_chains), OID_AUTO,
  190                     chain_name, CTLFLAG_RD, NULL, "sleepq chain stats");
  191                 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
  192                     "depth", CTLFLAG_RD, &sleepq_chains[i].sc_depth, 0, NULL);
  193                 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
  194                     "max_depth", CTLFLAG_RD, &sleepq_chains[i].sc_max_depth, 0,
  195                     NULL);
  196 #endif
  197         }
  198         sleepq_zone = uma_zcreate("SLEEPQUEUE", sizeof(struct sleepqueue),
  199 #ifdef INVARIANTS
  200             NULL, sleepq_dtor, sleepq_init, NULL, UMA_ALIGN_CACHE, 0);
  201 #else
  202             NULL, NULL, sleepq_init, NULL, UMA_ALIGN_CACHE, 0);
  203 #endif
  204         
  205         thread0.td_sleepqueue = sleepq_alloc();
  206 }
  207 
  208 /*
  209  * Get a sleep queue for a new thread.
  210  */
  211 struct sleepqueue *
  212 sleepq_alloc(void)
  213 {
  214 
  215         return (uma_zalloc(sleepq_zone, M_WAITOK));
  216 }
  217 
  218 /*
  219  * Free a sleep queue when a thread is destroyed.
  220  */
  221 void
  222 sleepq_free(struct sleepqueue *sq)
  223 {
  224 
  225         uma_zfree(sleepq_zone, sq);
  226 }
  227 
  228 /*
  229  * Lock the sleep queue chain associated with the specified wait channel.
  230  */
  231 void
  232 sleepq_lock(void *wchan)
  233 {
  234         struct sleepqueue_chain *sc;
  235 
  236         sc = SC_LOOKUP(wchan);
  237         mtx_lock_spin(&sc->sc_lock);
  238 }
  239 
  240 /*
  241  * Look up the sleep queue associated with a given wait channel in the hash
  242  * table locking the associated sleep queue chain.  If no queue is found in
  243  * the table, NULL is returned.
  244  */
  245 struct sleepqueue *
  246 sleepq_lookup(void *wchan)
  247 {
  248         struct sleepqueue_chain *sc;
  249         struct sleepqueue *sq;
  250 
  251         KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
  252         sc = SC_LOOKUP(wchan);
  253         mtx_assert(&sc->sc_lock, MA_OWNED);
  254         LIST_FOREACH(sq, &sc->sc_queues, sq_hash)
  255                 if (sq->sq_wchan == wchan)
  256                         return (sq);
  257         return (NULL);
  258 }
  259 
  260 /*
  261  * Unlock the sleep queue chain associated with a given wait channel.
  262  */
  263 void
  264 sleepq_release(void *wchan)
  265 {
  266         struct sleepqueue_chain *sc;
  267 
  268         sc = SC_LOOKUP(wchan);
  269         mtx_unlock_spin(&sc->sc_lock);
  270 }
  271 
  272 /*
  273  * Places the current thread on the sleep queue for the specified wait
  274  * channel.  If INVARIANTS is enabled, then it associates the passed in
  275  * lock with the sleepq to make sure it is held when that sleep queue is
  276  * woken up.
  277  */
  278 void
  279 sleepq_add(void *wchan, struct lock_object *lock, const char *wmesg, int flags,
  280     int queue)
  281 {
  282         struct sleepqueue_chain *sc;
  283         struct sleepqueue *sq;
  284         struct thread *td;
  285 
  286         td = curthread;
  287         sc = SC_LOOKUP(wchan);
  288         mtx_assert(&sc->sc_lock, MA_OWNED);
  289         MPASS(td->td_sleepqueue != NULL);
  290         MPASS(wchan != NULL);
  291         MPASS((queue >= 0) && (queue < NR_SLEEPQS));
  292 
  293         /* If this thread is not allowed to sleep, die a horrible death. */
  294         KASSERT(td->td_no_sleeping == 0,
  295             ("%s: td %p to sleep on wchan %p with sleeping prohibited",
  296             __func__, td, wchan));
  297 
  298         /* Look up the sleep queue associated with the wait channel 'wchan'. */
  299         sq = sleepq_lookup(wchan);
  300 
  301         /*
  302          * If the wait channel does not already have a sleep queue, use
  303          * this thread's sleep queue.  Otherwise, insert the current thread
  304          * into the sleep queue already in use by this wait channel.
  305          */
  306         if (sq == NULL) {
  307 #ifdef INVARIANTS
  308                 int i;
  309 
  310                 sq = td->td_sleepqueue;
  311                 for (i = 0; i < NR_SLEEPQS; i++) {
  312                         KASSERT(TAILQ_EMPTY(&sq->sq_blocked[i]),
  313                             ("thread's sleep queue %d is not empty", i));
  314                         KASSERT(sq->sq_blockedcnt[i] == 0,
  315                             ("thread's sleep queue %d count mismatches", i));
  316                 }
  317                 KASSERT(LIST_EMPTY(&sq->sq_free),
  318                     ("thread's sleep queue has a non-empty free list"));
  319                 KASSERT(sq->sq_wchan == NULL, ("stale sq_wchan pointer"));
  320                 sq->sq_lock = lock;
  321 #endif
  322 #ifdef SLEEPQUEUE_PROFILING
  323                 sc->sc_depth++;
  324                 if (sc->sc_depth > sc->sc_max_depth) {
  325                         sc->sc_max_depth = sc->sc_depth;
  326                         if (sc->sc_max_depth > sleepq_max_depth)
  327                                 sleepq_max_depth = sc->sc_max_depth;
  328                 }
  329 #endif
  330                 sq = td->td_sleepqueue;
  331                 LIST_INSERT_HEAD(&sc->sc_queues, sq, sq_hash);
  332                 sq->sq_wchan = wchan;
  333                 sq->sq_type = flags & SLEEPQ_TYPE;
  334         } else {
  335                 MPASS(wchan == sq->sq_wchan);
  336                 MPASS(lock == sq->sq_lock);
  337                 MPASS((flags & SLEEPQ_TYPE) == sq->sq_type);
  338                 LIST_INSERT_HEAD(&sq->sq_free, td->td_sleepqueue, sq_hash);
  339         }
  340         thread_lock(td);
  341         TAILQ_INSERT_TAIL(&sq->sq_blocked[queue], td, td_slpq);
  342         sq->sq_blockedcnt[queue]++;
  343         td->td_sleepqueue = NULL;
  344         td->td_sqqueue = queue;
  345         td->td_wchan = wchan;
  346         td->td_wmesg = wmesg;
  347         if (flags & SLEEPQ_INTERRUPTIBLE) {
  348                 td->td_flags |= TDF_SINTR;
  349                 td->td_flags &= ~TDF_SLEEPABORT;
  350         }
  351         thread_unlock(td);
  352 }
  353 
  354 /*
  355  * Sets a timeout that will remove the current thread from the specified
  356  * sleep queue after timo ticks if the thread has not already been awakened.
  357  */
  358 void
  359 sleepq_set_timeout_sbt(void *wchan, sbintime_t sbt, sbintime_t pr,
  360     int flags)
  361 {
  362         struct sleepqueue_chain *sc;
  363         struct thread *td;
  364 
  365         td = curthread;
  366         sc = SC_LOOKUP(wchan);
  367         mtx_assert(&sc->sc_lock, MA_OWNED);
  368         MPASS(TD_ON_SLEEPQ(td));
  369         MPASS(td->td_sleepqueue == NULL);
  370         MPASS(wchan != NULL);
  371         callout_reset_sbt_on(&td->td_slpcallout, sbt, pr,
  372             sleepq_timeout, td, PCPU_GET(cpuid), flags | C_DIRECT_EXEC);
  373 }
  374 
  375 /*
  376  * Return the number of actual sleepers for the specified queue.
  377  */
  378 u_int
  379 sleepq_sleepcnt(void *wchan, int queue)
  380 {
  381         struct sleepqueue *sq;
  382 
  383         KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
  384         MPASS((queue >= 0) && (queue < NR_SLEEPQS));
  385         sq = sleepq_lookup(wchan);
  386         if (sq == NULL)
  387                 return (0);
  388         return (sq->sq_blockedcnt[queue]);
  389 }
  390 
  391 /*
  392  * Marks the pending sleep of the current thread as interruptible and
  393  * makes an initial check for pending signals before putting a thread
  394  * to sleep. Enters and exits with the thread lock held.  Thread lock
  395  * may have transitioned from the sleepq lock to a run lock.
  396  */
  397 static int
  398 sleepq_catch_signals(void *wchan, int pri)
  399 {
  400         struct sleepqueue_chain *sc;
  401         struct sleepqueue *sq;
  402         struct thread *td;
  403         struct proc *p;
  404         struct sigacts *ps;
  405         int sig, ret;
  406 
  407         td = curthread;
  408         p = curproc;
  409         sc = SC_LOOKUP(wchan);
  410         mtx_assert(&sc->sc_lock, MA_OWNED);
  411         MPASS(wchan != NULL);
  412         if ((td->td_pflags & TDP_WAKEUP) != 0) {
  413                 td->td_pflags &= ~TDP_WAKEUP;
  414                 ret = EINTR;
  415                 thread_lock(td);
  416                 goto out;
  417         }
  418 
  419         /*
  420          * See if there are any pending signals for this thread.  If not
  421          * we can switch immediately.  Otherwise do the signal processing
  422          * directly.
  423          */
  424         thread_lock(td);
  425         if ((td->td_flags & (TDF_NEEDSIGCHK | TDF_NEEDSUSPCHK)) == 0) {
  426                 sleepq_switch(wchan, pri);
  427                 return (0);
  428         }
  429         thread_unlock(td);
  430         mtx_unlock_spin(&sc->sc_lock);
  431         CTR3(KTR_PROC, "sleepq catching signals: thread %p (pid %ld, %s)",
  432                 (void *)td, (long)p->p_pid, td->td_name);
  433         PROC_LOCK(p);
  434         ps = p->p_sigacts;
  435         mtx_lock(&ps->ps_mtx);
  436         sig = cursig(td);
  437         if (sig == 0) {
  438                 mtx_unlock(&ps->ps_mtx);
  439                 ret = thread_suspend_check(1);
  440                 MPASS(ret == 0 || ret == EINTR || ret == ERESTART);
  441         } else {
  442                 if (SIGISMEMBER(ps->ps_sigintr, sig))
  443                         ret = EINTR;
  444                 else
  445                         ret = ERESTART;
  446                 mtx_unlock(&ps->ps_mtx);
  447         }
  448         /*
  449          * Lock the per-process spinlock prior to dropping the PROC_LOCK
  450          * to avoid a signal delivery race.  PROC_LOCK, PROC_SLOCK, and
  451          * thread_lock() are currently held in tdsendsignal().
  452          */
  453         PROC_SLOCK(p);
  454         mtx_lock_spin(&sc->sc_lock);
  455         PROC_UNLOCK(p);
  456         thread_lock(td);
  457         PROC_SUNLOCK(p);
  458         if (ret == 0) {
  459                 sleepq_switch(wchan, pri);
  460                 return (0);
  461         }
  462 out:
  463         /*
  464          * There were pending signals and this thread is still
  465          * on the sleep queue, remove it from the sleep queue.
  466          */
  467         if (TD_ON_SLEEPQ(td)) {
  468                 sq = sleepq_lookup(wchan);
  469                 if (sleepq_resume_thread(sq, td, 0)) {
  470 #ifdef INVARIANTS
  471                         /*
  472                          * This thread hasn't gone to sleep yet, so it
  473                          * should not be swapped out.
  474                          */
  475                         panic("not waking up swapper");
  476 #endif
  477                 }
  478         }
  479         mtx_unlock_spin(&sc->sc_lock);
  480         MPASS(td->td_lock != &sc->sc_lock);
  481         return (ret);
  482 }
  483 
  484 /*
  485  * Switches to another thread if we are still asleep on a sleep queue.
  486  * Returns with thread lock.
  487  */
  488 static void
  489 sleepq_switch(void *wchan, int pri)
  490 {
  491         struct sleepqueue_chain *sc;
  492         struct sleepqueue *sq;
  493         struct thread *td;
  494 
  495         td = curthread;
  496         sc = SC_LOOKUP(wchan);
  497         mtx_assert(&sc->sc_lock, MA_OWNED);
  498         THREAD_LOCK_ASSERT(td, MA_OWNED);
  499 
  500         /* 
  501          * If we have a sleep queue, then we've already been woken up, so
  502          * just return.
  503          */
  504         if (td->td_sleepqueue != NULL) {
  505                 mtx_unlock_spin(&sc->sc_lock);
  506                 return;
  507         }
  508 
  509         /*
  510          * If TDF_TIMEOUT is set, then our sleep has been timed out
  511          * already but we are still on the sleep queue, so dequeue the
  512          * thread and return.
  513          */
  514         if (td->td_flags & TDF_TIMEOUT) {
  515                 MPASS(TD_ON_SLEEPQ(td));
  516                 sq = sleepq_lookup(wchan);
  517                 if (sleepq_resume_thread(sq, td, 0)) {
  518 #ifdef INVARIANTS
  519                         /*
  520                          * This thread hasn't gone to sleep yet, so it
  521                          * should not be swapped out.
  522                          */
  523                         panic("not waking up swapper");
  524 #endif
  525                 }
  526                 mtx_unlock_spin(&sc->sc_lock);
  527                 return;         
  528         }
  529 #ifdef SLEEPQUEUE_PROFILING
  530         if (prof_enabled)
  531                 sleepq_profile(td->td_wmesg);
  532 #endif
  533         MPASS(td->td_sleepqueue == NULL);
  534         sched_sleep(td, pri);
  535         thread_lock_set(td, &sc->sc_lock);
  536         SDT_PROBE0(sched, , , sleep);
  537         TD_SET_SLEEPING(td);
  538         mi_switch(SW_VOL | SWT_SLEEPQ, NULL);
  539         KASSERT(TD_IS_RUNNING(td), ("running but not TDS_RUNNING"));
  540         CTR3(KTR_PROC, "sleepq resume: thread %p (pid %ld, %s)",
  541             (void *)td, (long)td->td_proc->p_pid, (void *)td->td_name);
  542 }
  543 
  544 /*
  545  * Check to see if we timed out.
  546  */
  547 static int
  548 sleepq_check_timeout(void)
  549 {
  550         struct thread *td;
  551 
  552         td = curthread;
  553         THREAD_LOCK_ASSERT(td, MA_OWNED);
  554 
  555         /*
  556          * If TDF_TIMEOUT is set, we timed out.
  557          */
  558         if (td->td_flags & TDF_TIMEOUT) {
  559                 td->td_flags &= ~TDF_TIMEOUT;
  560                 return (EWOULDBLOCK);
  561         }
  562 
  563         /*
  564          * If TDF_TIMOFAIL is set, the timeout ran after we had
  565          * already been woken up.
  566          */
  567         if (td->td_flags & TDF_TIMOFAIL)
  568                 td->td_flags &= ~TDF_TIMOFAIL;
  569 
  570         /*
  571          * If callout_stop() fails, then the timeout is running on
  572          * another CPU, so synchronize with it to avoid having it
  573          * accidentally wake up a subsequent sleep.
  574          */
  575         else if (callout_stop(&td->td_slpcallout) == 0) {
  576                 td->td_flags |= TDF_TIMEOUT;
  577                 TD_SET_SLEEPING(td);
  578                 mi_switch(SW_INVOL | SWT_SLEEPQTIMO, NULL);
  579         }
  580         return (0);
  581 }
  582 
  583 /*
  584  * Check to see if we were awoken by a signal.
  585  */
  586 static int
  587 sleepq_check_signals(void)
  588 {
  589         struct thread *td;
  590 
  591         td = curthread;
  592         THREAD_LOCK_ASSERT(td, MA_OWNED);
  593 
  594         /* We are no longer in an interruptible sleep. */
  595         if (td->td_flags & TDF_SINTR)
  596                 td->td_flags &= ~TDF_SINTR;
  597 
  598         if (td->td_flags & TDF_SLEEPABORT) {
  599                 td->td_flags &= ~TDF_SLEEPABORT;
  600                 return (td->td_intrval);
  601         }
  602 
  603         return (0);
  604 }
  605 
  606 /*
  607  * Block the current thread until it is awakened from its sleep queue.
  608  */
  609 void
  610 sleepq_wait(void *wchan, int pri)
  611 {
  612         struct thread *td;
  613 
  614         td = curthread;
  615         MPASS(!(td->td_flags & TDF_SINTR));
  616         thread_lock(td);
  617         sleepq_switch(wchan, pri);
  618         thread_unlock(td);
  619 }
  620 
  621 /*
  622  * Block the current thread until it is awakened from its sleep queue
  623  * or it is interrupted by a signal.
  624  */
  625 int
  626 sleepq_wait_sig(void *wchan, int pri)
  627 {
  628         int rcatch;
  629         int rval;
  630 
  631         rcatch = sleepq_catch_signals(wchan, pri);
  632         rval = sleepq_check_signals();
  633         thread_unlock(curthread);
  634         if (rcatch)
  635                 return (rcatch);
  636         return (rval);
  637 }
  638 
  639 /*
  640  * Block the current thread until it is awakened from its sleep queue
  641  * or it times out while waiting.
  642  */
  643 int
  644 sleepq_timedwait(void *wchan, int pri)
  645 {
  646         struct thread *td;
  647         int rval;
  648 
  649         td = curthread;
  650         MPASS(!(td->td_flags & TDF_SINTR));
  651         thread_lock(td);
  652         sleepq_switch(wchan, pri);
  653         rval = sleepq_check_timeout();
  654         thread_unlock(td);
  655 
  656         return (rval);
  657 }
  658 
  659 /*
  660  * Block the current thread until it is awakened from its sleep queue,
  661  * it is interrupted by a signal, or it times out waiting to be awakened.
  662  */
  663 int
  664 sleepq_timedwait_sig(void *wchan, int pri)
  665 {
  666         int rcatch, rvalt, rvals;
  667 
  668         rcatch = sleepq_catch_signals(wchan, pri);
  669         rvalt = sleepq_check_timeout();
  670         rvals = sleepq_check_signals();
  671         thread_unlock(curthread);
  672         if (rcatch)
  673                 return (rcatch);
  674         if (rvals)
  675                 return (rvals);
  676         return (rvalt);
  677 }
  678 
  679 /*
  680  * Returns the type of sleepqueue given a waitchannel.
  681  */
  682 int
  683 sleepq_type(void *wchan)
  684 {
  685         struct sleepqueue *sq;
  686         int type;
  687 
  688         MPASS(wchan != NULL);
  689 
  690         sleepq_lock(wchan);
  691         sq = sleepq_lookup(wchan);
  692         if (sq == NULL) {
  693                 sleepq_release(wchan);
  694                 return (-1);
  695         }
  696         type = sq->sq_type;
  697         sleepq_release(wchan);
  698         return (type);
  699 }
  700 
  701 /*
  702  * Removes a thread from a sleep queue and makes it
  703  * runnable.
  704  */
  705 static int
  706 sleepq_resume_thread(struct sleepqueue *sq, struct thread *td, int pri)
  707 {
  708         struct sleepqueue_chain *sc;
  709 
  710         MPASS(td != NULL);
  711         MPASS(sq->sq_wchan != NULL);
  712         MPASS(td->td_wchan == sq->sq_wchan);
  713         MPASS(td->td_sqqueue < NR_SLEEPQS && td->td_sqqueue >= 0);
  714         THREAD_LOCK_ASSERT(td, MA_OWNED);
  715         sc = SC_LOOKUP(sq->sq_wchan);
  716         mtx_assert(&sc->sc_lock, MA_OWNED);
  717 
  718         SDT_PROBE2(sched, , , wakeup, td, td->td_proc);
  719 
  720         /* Remove the thread from the queue. */
  721         sq->sq_blockedcnt[td->td_sqqueue]--;
  722         TAILQ_REMOVE(&sq->sq_blocked[td->td_sqqueue], td, td_slpq);
  723 
  724         /*
  725          * Get a sleep queue for this thread.  If this is the last waiter,
  726          * use the queue itself and take it out of the chain, otherwise,
  727          * remove a queue from the free list.
  728          */
  729         if (LIST_EMPTY(&sq->sq_free)) {
  730                 td->td_sleepqueue = sq;
  731 #ifdef INVARIANTS
  732                 sq->sq_wchan = NULL;
  733 #endif
  734 #ifdef SLEEPQUEUE_PROFILING
  735                 sc->sc_depth--;
  736 #endif
  737         } else
  738                 td->td_sleepqueue = LIST_FIRST(&sq->sq_free);
  739         LIST_REMOVE(td->td_sleepqueue, sq_hash);
  740 
  741         td->td_wmesg = NULL;
  742         td->td_wchan = NULL;
  743         td->td_flags &= ~TDF_SINTR;
  744 
  745         CTR3(KTR_PROC, "sleepq_wakeup: thread %p (pid %ld, %s)",
  746             (void *)td, (long)td->td_proc->p_pid, td->td_name);
  747 
  748         /* Adjust priority if requested. */
  749         MPASS(pri == 0 || (pri >= PRI_MIN && pri <= PRI_MAX));
  750         if (pri != 0 && td->td_priority > pri &&
  751             PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
  752                 sched_prio(td, pri);
  753 
  754         /*
  755          * Note that thread td might not be sleeping if it is running
  756          * sleepq_catch_signals() on another CPU or is blocked on its
  757          * proc lock to check signals.  There's no need to mark the
  758          * thread runnable in that case.
  759          */
  760         if (TD_IS_SLEEPING(td)) {
  761                 TD_CLR_SLEEPING(td);
  762                 return (setrunnable(td));
  763         }
  764         return (0);
  765 }
  766 
  767 #ifdef INVARIANTS
  768 /*
  769  * UMA zone item deallocator.
  770  */
  771 static void
  772 sleepq_dtor(void *mem, int size, void *arg)
  773 {
  774         struct sleepqueue *sq;
  775         int i;
  776 
  777         sq = mem;
  778         for (i = 0; i < NR_SLEEPQS; i++) {
  779                 MPASS(TAILQ_EMPTY(&sq->sq_blocked[i]));
  780                 MPASS(sq->sq_blockedcnt[i] == 0);
  781         }
  782 }
  783 #endif
  784 
  785 /*
  786  * UMA zone item initializer.
  787  */
  788 static int
  789 sleepq_init(void *mem, int size, int flags)
  790 {
  791         struct sleepqueue *sq;
  792         int i;
  793 
  794         bzero(mem, size);
  795         sq = mem;
  796         for (i = 0; i < NR_SLEEPQS; i++) {
  797                 TAILQ_INIT(&sq->sq_blocked[i]);
  798                 sq->sq_blockedcnt[i] = 0;
  799         }
  800         LIST_INIT(&sq->sq_free);
  801         return (0);
  802 }
  803 
  804 /*
  805  * Find the highest priority thread sleeping on a wait channel and resume it.
  806  */
  807 int
  808 sleepq_signal(void *wchan, int flags, int pri, int queue)
  809 {
  810         struct sleepqueue *sq;
  811         struct thread *td, *besttd;
  812         int wakeup_swapper;
  813 
  814         CTR2(KTR_PROC, "sleepq_signal(%p, %d)", wchan, flags);
  815         KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
  816         MPASS((queue >= 0) && (queue < NR_SLEEPQS));
  817         sq = sleepq_lookup(wchan);
  818         if (sq == NULL)
  819                 return (0);
  820         KASSERT(sq->sq_type == (flags & SLEEPQ_TYPE),
  821             ("%s: mismatch between sleep/wakeup and cv_*", __func__));
  822 
  823         /*
  824          * Find the highest priority thread on the queue.  If there is a
  825          * tie, use the thread that first appears in the queue as it has
  826          * been sleeping the longest since threads are always added to
  827          * the tail of sleep queues.
  828          */
  829         besttd = NULL;
  830         TAILQ_FOREACH(td, &sq->sq_blocked[queue], td_slpq) {
  831                 if (besttd == NULL || td->td_priority < besttd->td_priority)
  832                         besttd = td;
  833         }
  834         MPASS(besttd != NULL);
  835         thread_lock(besttd);
  836         wakeup_swapper = sleepq_resume_thread(sq, besttd, pri);
  837         thread_unlock(besttd);
  838         return (wakeup_swapper);
  839 }
  840 
  841 /*
  842  * Resume all threads sleeping on a specified wait channel.
  843  */
  844 int
  845 sleepq_broadcast(void *wchan, int flags, int pri, int queue)
  846 {
  847         struct sleepqueue *sq;
  848         struct thread *td, *tdn;
  849         int wakeup_swapper;
  850 
  851         CTR2(KTR_PROC, "sleepq_broadcast(%p, %d)", wchan, flags);
  852         KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
  853         MPASS((queue >= 0) && (queue < NR_SLEEPQS));
  854         sq = sleepq_lookup(wchan);
  855         if (sq == NULL)
  856                 return (0);
  857         KASSERT(sq->sq_type == (flags & SLEEPQ_TYPE),
  858             ("%s: mismatch between sleep/wakeup and cv_*", __func__));
  859 
  860         /* Resume all blocked threads on the sleep queue. */
  861         wakeup_swapper = 0;
  862         TAILQ_FOREACH_SAFE(td, &sq->sq_blocked[queue], td_slpq, tdn) {
  863                 thread_lock(td);
  864                 if (sleepq_resume_thread(sq, td, pri))
  865                         wakeup_swapper = 1;
  866                 thread_unlock(td);
  867         }
  868         return (wakeup_swapper);
  869 }
  870 
  871 /*
  872  * Time sleeping threads out.  When the timeout expires, the thread is
  873  * removed from the sleep queue and made runnable if it is still asleep.
  874  */
  875 static void
  876 sleepq_timeout(void *arg)
  877 {
  878         struct sleepqueue_chain *sc;
  879         struct sleepqueue *sq;
  880         struct thread *td;
  881         void *wchan;
  882         int wakeup_swapper;
  883 
  884         td = arg;
  885         wakeup_swapper = 0;
  886         CTR3(KTR_PROC, "sleepq_timeout: thread %p (pid %ld, %s)",
  887             (void *)td, (long)td->td_proc->p_pid, (void *)td->td_name);
  888 
  889         /*
  890          * First, see if the thread is asleep and get the wait channel if
  891          * it is.
  892          */
  893         thread_lock(td);
  894         if (TD_IS_SLEEPING(td) && TD_ON_SLEEPQ(td)) {
  895                 wchan = td->td_wchan;
  896                 sc = SC_LOOKUP(wchan);
  897                 THREAD_LOCKPTR_ASSERT(td, &sc->sc_lock);
  898                 sq = sleepq_lookup(wchan);
  899                 MPASS(sq != NULL);
  900                 td->td_flags |= TDF_TIMEOUT;
  901                 wakeup_swapper = sleepq_resume_thread(sq, td, 0);
  902                 thread_unlock(td);
  903                 if (wakeup_swapper)
  904                         kick_proc0();
  905                 return;
  906         }
  907 
  908         /*
  909          * If the thread is on the SLEEPQ but isn't sleeping yet, it
  910          * can either be on another CPU in between sleepq_add() and
  911          * one of the sleepq_*wait*() routines or it can be in
  912          * sleepq_catch_signals().
  913          */
  914         if (TD_ON_SLEEPQ(td)) {
  915                 td->td_flags |= TDF_TIMEOUT;
  916                 thread_unlock(td);
  917                 return;
  918         }
  919 
  920         /*
  921          * Now check for the edge cases.  First, if TDF_TIMEOUT is set,
  922          * then the other thread has already yielded to us, so clear
  923          * the flag and resume it.  If TDF_TIMEOUT is not set, then the
  924          * we know that the other thread is not on a sleep queue, but it
  925          * hasn't resumed execution yet.  In that case, set TDF_TIMOFAIL
  926          * to let it know that the timeout has already run and doesn't
  927          * need to be canceled.
  928          */
  929         if (td->td_flags & TDF_TIMEOUT) {
  930                 MPASS(TD_IS_SLEEPING(td));
  931                 td->td_flags &= ~TDF_TIMEOUT;
  932                 TD_CLR_SLEEPING(td);
  933                 wakeup_swapper = setrunnable(td);
  934         } else
  935                 td->td_flags |= TDF_TIMOFAIL;
  936         thread_unlock(td);
  937         if (wakeup_swapper)
  938                 kick_proc0();
  939 }
  940 
  941 /*
  942  * Resumes a specific thread from the sleep queue associated with a specific
  943  * wait channel if it is on that queue.
  944  */
  945 void
  946 sleepq_remove(struct thread *td, void *wchan)
  947 {
  948         struct sleepqueue *sq;
  949         int wakeup_swapper;
  950 
  951         /*
  952          * Look up the sleep queue for this wait channel, then re-check
  953          * that the thread is asleep on that channel, if it is not, then
  954          * bail.
  955          */
  956         MPASS(wchan != NULL);
  957         sleepq_lock(wchan);
  958         sq = sleepq_lookup(wchan);
  959         /*
  960          * We can not lock the thread here as it may be sleeping on a
  961          * different sleepq.  However, holding the sleepq lock for this
  962          * wchan can guarantee that we do not miss a wakeup for this
  963          * channel.  The asserts below will catch any false positives.
  964          */
  965         if (!TD_ON_SLEEPQ(td) || td->td_wchan != wchan) {
  966                 sleepq_release(wchan);
  967                 return;
  968         }
  969         /* Thread is asleep on sleep queue sq, so wake it up. */
  970         thread_lock(td);
  971         MPASS(sq != NULL);
  972         MPASS(td->td_wchan == wchan);
  973         wakeup_swapper = sleepq_resume_thread(sq, td, 0);
  974         thread_unlock(td);
  975         sleepq_release(wchan);
  976         if (wakeup_swapper)
  977                 kick_proc0();
  978 }
  979 
  980 /*
  981  * Abort a thread as if an interrupt had occurred.  Only abort
  982  * interruptible waits (unfortunately it isn't safe to abort others).
  983  */
  984 int
  985 sleepq_abort(struct thread *td, int intrval)
  986 {
  987         struct sleepqueue *sq;
  988         void *wchan;
  989 
  990         THREAD_LOCK_ASSERT(td, MA_OWNED);
  991         MPASS(TD_ON_SLEEPQ(td));
  992         MPASS(td->td_flags & TDF_SINTR);
  993         MPASS(intrval == EINTR || intrval == ERESTART);
  994 
  995         /*
  996          * If the TDF_TIMEOUT flag is set, just leave. A
  997          * timeout is scheduled anyhow.
  998          */
  999         if (td->td_flags & TDF_TIMEOUT)
 1000                 return (0);
 1001 
 1002         CTR3(KTR_PROC, "sleepq_abort: thread %p (pid %ld, %s)",
 1003             (void *)td, (long)td->td_proc->p_pid, (void *)td->td_name);
 1004         td->td_intrval = intrval;
 1005         td->td_flags |= TDF_SLEEPABORT;
 1006         /*
 1007          * If the thread has not slept yet it will find the signal in
 1008          * sleepq_catch_signals() and call sleepq_resume_thread.  Otherwise
 1009          * we have to do it here.
 1010          */
 1011         if (!TD_IS_SLEEPING(td))
 1012                 return (0);
 1013         wchan = td->td_wchan;
 1014         MPASS(wchan != NULL);
 1015         sq = sleepq_lookup(wchan);
 1016         MPASS(sq != NULL);
 1017 
 1018         /* Thread is asleep on sleep queue sq, so wake it up. */
 1019         return (sleepq_resume_thread(sq, td, 0));
 1020 }
 1021 
 1022 #ifdef SLEEPQUEUE_PROFILING
 1023 #define SLEEPQ_PROF_LOCATIONS   1024
 1024 #define SLEEPQ_SBUFSIZE         512
 1025 struct sleepq_prof {
 1026         LIST_ENTRY(sleepq_prof) sp_link;
 1027         const char      *sp_wmesg;
 1028         long            sp_count;
 1029 };
 1030 
 1031 LIST_HEAD(sqphead, sleepq_prof);
 1032 
 1033 struct sqphead sleepq_prof_free;
 1034 struct sqphead sleepq_hash[SC_TABLESIZE];
 1035 static struct sleepq_prof sleepq_profent[SLEEPQ_PROF_LOCATIONS];
 1036 static struct mtx sleepq_prof_lock;
 1037 MTX_SYSINIT(sleepq_prof_lock, &sleepq_prof_lock, "sleepq_prof", MTX_SPIN);
 1038 
 1039 static void
 1040 sleepq_profile(const char *wmesg)
 1041 {
 1042         struct sleepq_prof *sp;
 1043 
 1044         mtx_lock_spin(&sleepq_prof_lock);
 1045         if (prof_enabled == 0)
 1046                 goto unlock;
 1047         LIST_FOREACH(sp, &sleepq_hash[SC_HASH(wmesg)], sp_link)
 1048                 if (sp->sp_wmesg == wmesg)
 1049                         goto done;
 1050         sp = LIST_FIRST(&sleepq_prof_free);
 1051         if (sp == NULL)
 1052                 goto unlock;
 1053         sp->sp_wmesg = wmesg;
 1054         LIST_REMOVE(sp, sp_link);
 1055         LIST_INSERT_HEAD(&sleepq_hash[SC_HASH(wmesg)], sp, sp_link);
 1056 done:
 1057         sp->sp_count++;
 1058 unlock:
 1059         mtx_unlock_spin(&sleepq_prof_lock);
 1060         return;
 1061 }
 1062 
 1063 static void
 1064 sleepq_prof_reset(void)
 1065 {
 1066         struct sleepq_prof *sp;
 1067         int enabled;
 1068         int i;
 1069 
 1070         mtx_lock_spin(&sleepq_prof_lock);
 1071         enabled = prof_enabled;
 1072         prof_enabled = 0;
 1073         for (i = 0; i < SC_TABLESIZE; i++)
 1074                 LIST_INIT(&sleepq_hash[i]);
 1075         LIST_INIT(&sleepq_prof_free);
 1076         for (i = 0; i < SLEEPQ_PROF_LOCATIONS; i++) {
 1077                 sp = &sleepq_profent[i];
 1078                 sp->sp_wmesg = NULL;
 1079                 sp->sp_count = 0;
 1080                 LIST_INSERT_HEAD(&sleepq_prof_free, sp, sp_link);
 1081         }
 1082         prof_enabled = enabled;
 1083         mtx_unlock_spin(&sleepq_prof_lock);
 1084 }
 1085 
 1086 static int
 1087 enable_sleepq_prof(SYSCTL_HANDLER_ARGS)
 1088 {
 1089         int error, v;
 1090 
 1091         v = prof_enabled;
 1092         error = sysctl_handle_int(oidp, &v, v, req);
 1093         if (error)
 1094                 return (error);
 1095         if (req->newptr == NULL)
 1096                 return (error);
 1097         if (v == prof_enabled)
 1098                 return (0);
 1099         if (v == 1)
 1100                 sleepq_prof_reset();
 1101         mtx_lock_spin(&sleepq_prof_lock);
 1102         prof_enabled = !!v;
 1103         mtx_unlock_spin(&sleepq_prof_lock);
 1104 
 1105         return (0);
 1106 }
 1107 
 1108 static int
 1109 reset_sleepq_prof_stats(SYSCTL_HANDLER_ARGS)
 1110 {
 1111         int error, v;
 1112 
 1113         v = 0;
 1114         error = sysctl_handle_int(oidp, &v, 0, req);
 1115         if (error)
 1116                 return (error);
 1117         if (req->newptr == NULL)
 1118                 return (error);
 1119         if (v == 0)
 1120                 return (0);
 1121         sleepq_prof_reset();
 1122 
 1123         return (0);
 1124 }
 1125 
 1126 static int
 1127 dump_sleepq_prof_stats(SYSCTL_HANDLER_ARGS)
 1128 {
 1129         struct sleepq_prof *sp;
 1130         struct sbuf *sb;
 1131         int enabled;
 1132         int error;
 1133         int i;
 1134 
 1135         error = sysctl_wire_old_buffer(req, 0);
 1136         if (error != 0)
 1137                 return (error);
 1138         sb = sbuf_new_for_sysctl(NULL, NULL, SLEEPQ_SBUFSIZE, req);
 1139         sbuf_printf(sb, "\nwmesg\tcount\n");
 1140         enabled = prof_enabled;
 1141         mtx_lock_spin(&sleepq_prof_lock);
 1142         prof_enabled = 0;
 1143         mtx_unlock_spin(&sleepq_prof_lock);
 1144         for (i = 0; i < SC_TABLESIZE; i++) {
 1145                 LIST_FOREACH(sp, &sleepq_hash[i], sp_link) {
 1146                         sbuf_printf(sb, "%s\t%ld\n",
 1147                             sp->sp_wmesg, sp->sp_count);
 1148                 }
 1149         }
 1150         mtx_lock_spin(&sleepq_prof_lock);
 1151         prof_enabled = enabled;
 1152         mtx_unlock_spin(&sleepq_prof_lock);
 1153 
 1154         error = sbuf_finish(sb);
 1155         sbuf_delete(sb);
 1156         return (error);
 1157 }
 1158 
 1159 SYSCTL_PROC(_debug_sleepq, OID_AUTO, stats, CTLTYPE_STRING | CTLFLAG_RD,
 1160     NULL, 0, dump_sleepq_prof_stats, "A", "Sleepqueue profiling statistics");
 1161 SYSCTL_PROC(_debug_sleepq, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_RW,
 1162     NULL, 0, reset_sleepq_prof_stats, "I",
 1163     "Reset sleepqueue profiling statistics");
 1164 SYSCTL_PROC(_debug_sleepq, OID_AUTO, enable, CTLTYPE_INT | CTLFLAG_RW,
 1165     NULL, 0, enable_sleepq_prof, "I", "Enable sleepqueue profiling");
 1166 #endif
 1167 
 1168 #ifdef DDB
 1169 DB_SHOW_COMMAND(sleepq, db_show_sleepqueue)
 1170 {
 1171         struct sleepqueue_chain *sc;
 1172         struct sleepqueue *sq;
 1173 #ifdef INVARIANTS
 1174         struct lock_object *lock;
 1175 #endif
 1176         struct thread *td;
 1177         void *wchan;
 1178         int i;
 1179 
 1180         if (!have_addr)
 1181                 return;
 1182 
 1183         /*
 1184          * First, see if there is an active sleep queue for the wait channel
 1185          * indicated by the address.
 1186          */
 1187         wchan = (void *)addr;
 1188         sc = SC_LOOKUP(wchan);
 1189         LIST_FOREACH(sq, &sc->sc_queues, sq_hash)
 1190                 if (sq->sq_wchan == wchan)
 1191                         goto found;
 1192 
 1193         /*
 1194          * Second, see if there is an active sleep queue at the address
 1195          * indicated.
 1196          */
 1197         for (i = 0; i < SC_TABLESIZE; i++)
 1198                 LIST_FOREACH(sq, &sleepq_chains[i].sc_queues, sq_hash) {
 1199                         if (sq == (struct sleepqueue *)addr)
 1200                                 goto found;
 1201                 }
 1202 
 1203         db_printf("Unable to locate a sleep queue via %p\n", (void *)addr);
 1204         return;
 1205 found:
 1206         db_printf("Wait channel: %p\n", sq->sq_wchan);
 1207         db_printf("Queue type: %d\n", sq->sq_type);
 1208 #ifdef INVARIANTS
 1209         if (sq->sq_lock) {
 1210                 lock = sq->sq_lock;
 1211                 db_printf("Associated Interlock: %p - (%s) %s\n", lock,
 1212                     LOCK_CLASS(lock)->lc_name, lock->lo_name);
 1213         }
 1214 #endif
 1215         db_printf("Blocked threads:\n");
 1216         for (i = 0; i < NR_SLEEPQS; i++) {
 1217                 db_printf("\nQueue[%d]:\n", i);
 1218                 if (TAILQ_EMPTY(&sq->sq_blocked[i]))
 1219                         db_printf("\tempty\n");
 1220                 else
 1221                         TAILQ_FOREACH(td, &sq->sq_blocked[0],
 1222                                       td_slpq) {
 1223                                 db_printf("\t%p (tid %d, pid %d, \"%s\")\n", td,
 1224                                           td->td_tid, td->td_proc->p_pid,
 1225                                           td->td_name);
 1226                         }
 1227                 db_printf("(expected: %u)\n", sq->sq_blockedcnt[i]);
 1228         }
 1229 }
 1230 
 1231 /* Alias 'show sleepqueue' to 'show sleepq'. */
 1232 DB_SHOW_ALIAS(sleepqueue, db_show_sleepqueue);
 1233 #endif

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