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  * 3. Neither the name of the author nor the names of any co-contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  */
   29 
   30 /*
   31  * Implementation of sleep queues used to hold queue of threads blocked on
   32  * a wait channel.  Sleep queues different from turnstiles in that wait
   33  * channels are not owned by anyone, so there is no priority propagation.
   34  * Sleep queues can also provide a timeout and can also be interrupted by
   35  * signals.  That said, there are several similarities between the turnstile
   36  * and sleep queue implementations.  (Note: turnstiles were implemented
   37  * first.)  For example, both use a hash table of the same size where each
   38  * bucket is referred to as a "chain" that contains both a spin lock and
   39  * a linked list of queues.  An individual queue is located by using a hash
   40  * to pick a chain, locking the chain, and then walking the chain searching
   41  * for the queue.  This means that a wait channel object does not need to
   42  * embed it's queue head just as locks do not embed their turnstile queue
   43  * head.  Threads also carry around a sleep queue that they lend to the
   44  * wait channel when blocking.  Just as in turnstiles, the queue includes
   45  * a free list of the sleep queues of other threads blocked on the same
   46  * wait channel in the case of multiple waiters.
   47  *
   48  * Some additional functionality provided by sleep queues include the
   49  * ability to set a timeout.  The timeout is managed using a per-thread
   50  * callout that resumes a thread if it is asleep.  A thread may also
   51  * catch signals while it is asleep (aka an interruptible sleep).  The
   52  * signal code uses sleepq_abort() to interrupt a sleeping thread.  Finally,
   53  * sleep queues also provide some extra assertions.  One is not allowed to
   54  * mix the sleep/wakeup and cv APIs for a given wait channel.  Also, one
   55  * must consistently use the same lock to synchronize with a wait channel,
   56  * though this check is currently only a warning for sleep/wakeup due to
   57  * pre-existing abuse of that API.  The same lock must also be held when
   58  * awakening threads, though that is currently only enforced for condition
   59  * variables.
   60  */
   61 
   62 #include <sys/cdefs.h>
   63 __FBSDID("$FreeBSD: releng/8.2/sys/kern/subr_sleepqueue.c 202966 2010-01-25 12:05:51Z attilio $");
   64 
   65 #include "opt_sleepqueue_profiling.h"
   66 #include "opt_ddb.h"
   67 #include "opt_sched.h"
   68 
   69 #include <sys/param.h>
   70 #include <sys/systm.h>
   71 #include <sys/lock.h>
   72 #include <sys/kernel.h>
   73 #include <sys/ktr.h>
   74 #include <sys/mutex.h>
   75 #include <sys/proc.h>
   76 #include <sys/sbuf.h>
   77 #include <sys/sched.h>
   78 #include <sys/signalvar.h>
   79 #include <sys/sleepqueue.h>
   80 #include <sys/sysctl.h>
   81 
   82 #include <vm/uma.h>
   83 
   84 #ifdef DDB
   85 #include <ddb/ddb.h>
   86 #endif
   87 
   88 /*
   89  * Constants for the hash table of sleep queue chains.  These constants are
   90  * the same ones that 4BSD (and possibly earlier versions of BSD) used.
   91  * Basically, we ignore the lower 8 bits of the address since most wait
   92  * channel pointers are aligned and only look at the next 7 bits for the
   93  * hash.  SC_TABLESIZE must be a power of two for SC_MASK to work properly.
   94  */
   95 #define SC_TABLESIZE    128                     /* Must be power of 2. */
   96 #define SC_MASK         (SC_TABLESIZE - 1)
   97 #define SC_SHIFT        8
   98 #define SC_HASH(wc)     (((uintptr_t)(wc) >> SC_SHIFT) & SC_MASK)
   99 #define SC_LOOKUP(wc)   &sleepq_chains[SC_HASH(wc)]
  100 #define NR_SLEEPQS      2
  101 /*
  102  * There two different lists of sleep queues.  Both lists are connected
  103  * via the sq_hash entries.  The first list is the sleep queue chain list
  104  * that a sleep queue is on when it is attached to a wait channel.  The
  105  * second list is the free list hung off of a sleep queue that is attached
  106  * to a wait channel.
  107  *
  108  * Each sleep queue also contains the wait channel it is attached to, the
  109  * list of threads blocked on that wait channel, flags specific to the
  110  * wait channel, and the lock used to synchronize with a wait channel.
  111  * The flags are used to catch mismatches between the various consumers
  112  * of the sleep queue API (e.g. sleep/wakeup and condition variables).
  113  * The lock pointer is only used when invariants are enabled for various
  114  * debugging checks.
  115  *
  116  * Locking key:
  117  *  c - sleep queue chain lock
  118  */
  119 struct sleepqueue {
  120         TAILQ_HEAD(, thread) sq_blocked[NR_SLEEPQS];    /* (c) Blocked threads. */
  121         u_int sq_blockedcnt[NR_SLEEPQS];        /* (c) N. of blocked threads. */
  122         LIST_ENTRY(sleepqueue) sq_hash;         /* (c) Chain and free list. */
  123         LIST_HEAD(, sleepqueue) sq_free;        /* (c) Free queues. */
  124         void    *sq_wchan;                      /* (c) Wait channel. */
  125         int     sq_type;                        /* (c) Queue type. */
  126 #ifdef INVARIANTS
  127         struct lock_object *sq_lock;            /* (c) Associated lock. */
  128 #endif
  129 };
  130 
  131 struct sleepqueue_chain {
  132         LIST_HEAD(, sleepqueue) sc_queues;      /* List of sleep queues. */
  133         struct mtx sc_lock;                     /* Spin lock for this chain. */
  134 #ifdef SLEEPQUEUE_PROFILING
  135         u_int   sc_depth;                       /* Length of sc_queues. */
  136         u_int   sc_max_depth;                   /* Max length of sc_queues. */
  137 #endif
  138 };
  139 
  140 #ifdef SLEEPQUEUE_PROFILING
  141 u_int sleepq_max_depth;
  142 SYSCTL_NODE(_debug, OID_AUTO, sleepq, CTLFLAG_RD, 0, "sleepq profiling");
  143 SYSCTL_NODE(_debug_sleepq, OID_AUTO, chains, CTLFLAG_RD, 0,
  144     "sleepq chain stats");
  145 SYSCTL_UINT(_debug_sleepq, OID_AUTO, max_depth, CTLFLAG_RD, &sleepq_max_depth,
  146     0, "maxmimum depth achieved of a single chain");
  147 
  148 static void     sleepq_profile(const char *wmesg);
  149 static int      prof_enabled;
  150 #endif
  151 static struct sleepqueue_chain sleepq_chains[SC_TABLESIZE];
  152 static uma_zone_t sleepq_zone;
  153 
  154 /*
  155  * Prototypes for non-exported routines.
  156  */
  157 static int      sleepq_catch_signals(void *wchan, int pri);
  158 static int      sleepq_check_signals(void);
  159 static int      sleepq_check_timeout(void);
  160 #ifdef INVARIANTS
  161 static void     sleepq_dtor(void *mem, int size, void *arg);
  162 #endif
  163 static int      sleepq_init(void *mem, int size, int flags);
  164 static int      sleepq_resume_thread(struct sleepqueue *sq, struct thread *td,
  165                     int pri);
  166 static void     sleepq_switch(void *wchan, int pri);
  167 static void     sleepq_timeout(void *arg);
  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_pflags & TDP_NOSLEEPING),
  295             ("Trying sleep, but thread marked as sleeping prohibited"));
  296 
  297         /* Look up the sleep queue associated with the wait channel 'wchan'. */
  298         sq = sleepq_lookup(wchan);
  299 
  300         /*
  301          * If the wait channel does not already have a sleep queue, use
  302          * this thread's sleep queue.  Otherwise, insert the current thread
  303          * into the sleep queue already in use by this wait channel.
  304          */
  305         if (sq == NULL) {
  306 #ifdef INVARIANTS
  307                 int i;
  308 
  309                 sq = td->td_sleepqueue;
  310                 for (i = 0; i < NR_SLEEPQS; i++) {
  311                         KASSERT(TAILQ_EMPTY(&sq->sq_blocked[i]),
  312                             ("thread's sleep queue %d is not empty", i));
  313                         KASSERT(sq->sq_blockedcnt[i] == 0,
  314                             ("thread's sleep queue %d count mismatches", i));
  315                 }
  316                 KASSERT(LIST_EMPTY(&sq->sq_free),
  317                     ("thread's sleep queue has a non-empty free list"));
  318                 KASSERT(sq->sq_wchan == NULL, ("stale sq_wchan pointer"));
  319                 sq->sq_lock = lock;
  320 #endif
  321 #ifdef SLEEPQUEUE_PROFILING
  322                 sc->sc_depth++;
  323                 if (sc->sc_depth > sc->sc_max_depth) {
  324                         sc->sc_max_depth = sc->sc_depth;
  325                         if (sc->sc_max_depth > sleepq_max_depth)
  326                                 sleepq_max_depth = sc->sc_max_depth;
  327                 }
  328 #endif
  329                 sq = td->td_sleepqueue;
  330                 LIST_INSERT_HEAD(&sc->sc_queues, sq, sq_hash);
  331                 sq->sq_wchan = wchan;
  332                 sq->sq_type = flags & SLEEPQ_TYPE;
  333         } else {
  334                 MPASS(wchan == sq->sq_wchan);
  335                 MPASS(lock == sq->sq_lock);
  336                 MPASS((flags & SLEEPQ_TYPE) == sq->sq_type);
  337                 LIST_INSERT_HEAD(&sq->sq_free, td->td_sleepqueue, sq_hash);
  338         }
  339         thread_lock(td);
  340         TAILQ_INSERT_TAIL(&sq->sq_blocked[queue], td, td_slpq);
  341         sq->sq_blockedcnt[queue]++;
  342         td->td_sleepqueue = NULL;
  343         td->td_sqqueue = queue;
  344         td->td_wchan = wchan;
  345         td->td_wmesg = wmesg;
  346         if (flags & SLEEPQ_INTERRUPTIBLE) {
  347                 td->td_flags |= TDF_SINTR;
  348                 td->td_flags &= ~TDF_SLEEPABORT;
  349                 if (flags & SLEEPQ_STOP_ON_BDRY)
  350                         td->td_flags |= TDF_SBDRY;
  351         }
  352         thread_unlock(td);
  353 }
  354 
  355 /*
  356  * Sets a timeout that will remove the current thread from the specified
  357  * sleep queue after timo ticks if the thread has not already been awakened.
  358  */
  359 void
  360 sleepq_set_timeout(void *wchan, int timo)
  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_curcpu(&td->td_slpcallout, timo, sleepq_timeout, td);
  372 }
  373 
  374 /*
  375  * Return the number of actual sleepers for the specified queue.
  376  */
  377 u_int
  378 sleepq_sleepcnt(void *wchan, int queue)
  379 {
  380         struct sleepqueue *sq;
  381 
  382         KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
  383         MPASS((queue >= 0) && (queue < NR_SLEEPQS));
  384         sq = sleepq_lookup(wchan);
  385         if (sq == NULL)
  386                 return (0);
  387         return (sq->sq_blockedcnt[queue]);
  388 }
  389 
  390 /*
  391  * Marks the pending sleep of the current thread as interruptible and
  392  * makes an initial check for pending signals before putting a thread
  393  * to sleep. Enters and exits with the thread lock held.  Thread lock
  394  * may have transitioned from the sleepq lock to a run lock.
  395  */
  396 static int
  397 sleepq_catch_signals(void *wchan, int pri)
  398 {
  399         struct sleepqueue_chain *sc;
  400         struct sleepqueue *sq;
  401         struct thread *td;
  402         struct proc *p;
  403         struct sigacts *ps;
  404         int sig, ret, stop_allowed;
  405 
  406         td = curthread;
  407         p = curproc;
  408         sc = SC_LOOKUP(wchan);
  409         mtx_assert(&sc->sc_lock, MA_OWNED);
  410         MPASS(wchan != NULL);
  411         /*
  412          * See if there are any pending signals for this thread.  If not
  413          * we can switch immediately.  Otherwise do the signal processing
  414          * directly.
  415          */
  416         thread_lock(td);
  417         if ((td->td_flags & (TDF_NEEDSIGCHK | TDF_NEEDSUSPCHK)) == 0) {
  418                 sleepq_switch(wchan, pri);
  419                 return (0);
  420         }
  421         stop_allowed = (td->td_flags & TDF_SBDRY) ? SIG_STOP_NOT_ALLOWED :
  422             SIG_STOP_ALLOWED;
  423         thread_unlock(td);
  424         mtx_unlock_spin(&sc->sc_lock);
  425         CTR3(KTR_PROC, "sleepq catching signals: thread %p (pid %ld, %s)",
  426                 (void *)td, (long)p->p_pid, td->td_name);
  427         PROC_LOCK(p);
  428         ps = p->p_sigacts;
  429         mtx_lock(&ps->ps_mtx);
  430         sig = cursig(td, stop_allowed);
  431         if (sig == 0) {
  432                 mtx_unlock(&ps->ps_mtx);
  433                 ret = thread_suspend_check(1);
  434                 MPASS(ret == 0 || ret == EINTR || ret == ERESTART);
  435         } else {
  436                 if (SIGISMEMBER(ps->ps_sigintr, sig))
  437                         ret = EINTR;
  438                 else
  439                         ret = ERESTART;
  440                 mtx_unlock(&ps->ps_mtx);
  441         }
  442         /*
  443          * Lock the per-process spinlock prior to dropping the PROC_LOCK
  444          * to avoid a signal delivery race.  PROC_LOCK, PROC_SLOCK, and
  445          * thread_lock() are currently held in tdsignal().
  446          */
  447         PROC_SLOCK(p);
  448         mtx_lock_spin(&sc->sc_lock);
  449         PROC_UNLOCK(p);
  450         thread_lock(td);
  451         PROC_SUNLOCK(p);
  452         if (ret == 0) {
  453                 sleepq_switch(wchan, pri);
  454                 return (0);
  455         }
  456         /*
  457          * There were pending signals and this thread is still
  458          * on the sleep queue, remove it from the sleep queue.
  459          */
  460         if (TD_ON_SLEEPQ(td)) {
  461                 sq = sleepq_lookup(wchan);
  462                 if (sleepq_resume_thread(sq, td, 0)) {
  463 #ifdef INVARIANTS
  464                         /*
  465                          * This thread hasn't gone to sleep yet, so it
  466                          * should not be swapped out.
  467                          */
  468                         panic("not waking up swapper");
  469 #endif
  470                 }
  471         }
  472         mtx_unlock_spin(&sc->sc_lock);
  473         MPASS(td->td_lock != &sc->sc_lock);
  474         return (ret);
  475 }
  476 
  477 /*
  478  * Switches to another thread if we are still asleep on a sleep queue.
  479  * Returns with thread lock.
  480  */
  481 static void
  482 sleepq_switch(void *wchan, int pri)
  483 {
  484         struct sleepqueue_chain *sc;
  485         struct sleepqueue *sq;
  486         struct thread *td;
  487 
  488         td = curthread;
  489         sc = SC_LOOKUP(wchan);
  490         mtx_assert(&sc->sc_lock, MA_OWNED);
  491         THREAD_LOCK_ASSERT(td, MA_OWNED);
  492 
  493         /* 
  494          * If we have a sleep queue, then we've already been woken up, so
  495          * just return.
  496          */
  497         if (td->td_sleepqueue != NULL) {
  498                 mtx_unlock_spin(&sc->sc_lock);
  499                 return;
  500         }
  501 
  502         /*
  503          * If TDF_TIMEOUT is set, then our sleep has been timed out
  504          * already but we are still on the sleep queue, so dequeue the
  505          * thread and return.
  506          */
  507         if (td->td_flags & TDF_TIMEOUT) {
  508                 MPASS(TD_ON_SLEEPQ(td));
  509                 sq = sleepq_lookup(wchan);
  510                 if (sleepq_resume_thread(sq, td, 0)) {
  511 #ifdef INVARIANTS
  512                         /*
  513                          * This thread hasn't gone to sleep yet, so it
  514                          * should not be swapped out.
  515                          */
  516                         panic("not waking up swapper");
  517 #endif
  518                 }
  519                 mtx_unlock_spin(&sc->sc_lock);
  520                 return;         
  521         }
  522 #ifdef SLEEPQUEUE_PROFILING
  523         if (prof_enabled)
  524                 sleepq_profile(td->td_wmesg);
  525 #endif
  526         MPASS(td->td_sleepqueue == NULL);
  527         sched_sleep(td, pri);
  528         thread_lock_set(td, &sc->sc_lock);
  529         TD_SET_SLEEPING(td);
  530         mi_switch(SW_VOL | SWT_SLEEPQ, NULL);
  531         KASSERT(TD_IS_RUNNING(td), ("running but not TDS_RUNNING"));
  532         CTR3(KTR_PROC, "sleepq resume: thread %p (pid %ld, %s)",
  533             (void *)td, (long)td->td_proc->p_pid, (void *)td->td_name);
  534 }
  535 
  536 /*
  537  * Check to see if we timed out.
  538  */
  539 static int
  540 sleepq_check_timeout(void)
  541 {
  542         struct thread *td;
  543 
  544         td = curthread;
  545         THREAD_LOCK_ASSERT(td, MA_OWNED);
  546 
  547         /*
  548          * If TDF_TIMEOUT is set, we timed out.
  549          */
  550         if (td->td_flags & TDF_TIMEOUT) {
  551                 td->td_flags &= ~TDF_TIMEOUT;
  552                 return (EWOULDBLOCK);
  553         }
  554 
  555         /*
  556          * If TDF_TIMOFAIL is set, the timeout ran after we had
  557          * already been woken up.
  558          */
  559         if (td->td_flags & TDF_TIMOFAIL)
  560                 td->td_flags &= ~TDF_TIMOFAIL;
  561 
  562         /*
  563          * If callout_stop() fails, then the timeout is running on
  564          * another CPU, so synchronize with it to avoid having it
  565          * accidentally wake up a subsequent sleep.
  566          */
  567         else if (callout_stop(&td->td_slpcallout) == 0) {
  568                 td->td_flags |= TDF_TIMEOUT;
  569                 TD_SET_SLEEPING(td);
  570                 mi_switch(SW_INVOL | SWT_SLEEPQTIMO, NULL);
  571         }
  572         return (0);
  573 }
  574 
  575 /*
  576  * Check to see if we were awoken by a signal.
  577  */
  578 static int
  579 sleepq_check_signals(void)
  580 {
  581         struct thread *td;
  582 
  583         td = curthread;
  584         THREAD_LOCK_ASSERT(td, MA_OWNED);
  585 
  586         /* We are no longer in an interruptible sleep. */
  587         if (td->td_flags & TDF_SINTR)
  588                 td->td_flags &= ~(TDF_SINTR | TDF_SBDRY);
  589 
  590         if (td->td_flags & TDF_SLEEPABORT) {
  591                 td->td_flags &= ~TDF_SLEEPABORT;
  592                 return (td->td_intrval);
  593         }
  594 
  595         return (0);
  596 }
  597 
  598 /*
  599  * Block the current thread until it is awakened from its sleep queue.
  600  */
  601 void
  602 sleepq_wait(void *wchan, int pri)
  603 {
  604         struct thread *td;
  605 
  606         td = curthread;
  607         MPASS(!(td->td_flags & TDF_SINTR));
  608         thread_lock(td);
  609         sleepq_switch(wchan, pri);
  610         thread_unlock(td);
  611 }
  612 
  613 /*
  614  * Block the current thread until it is awakened from its sleep queue
  615  * or it is interrupted by a signal.
  616  */
  617 int
  618 sleepq_wait_sig(void *wchan, int pri)
  619 {
  620         int rcatch;
  621         int rval;
  622 
  623         rcatch = sleepq_catch_signals(wchan, pri);
  624         rval = sleepq_check_signals();
  625         thread_unlock(curthread);
  626         if (rcatch)
  627                 return (rcatch);
  628         return (rval);
  629 }
  630 
  631 /*
  632  * Block the current thread until it is awakened from its sleep queue
  633  * or it times out while waiting.
  634  */
  635 int
  636 sleepq_timedwait(void *wchan, int pri)
  637 {
  638         struct thread *td;
  639         int rval;
  640 
  641         td = curthread;
  642         MPASS(!(td->td_flags & TDF_SINTR));
  643         thread_lock(td);
  644         sleepq_switch(wchan, pri);
  645         rval = sleepq_check_timeout();
  646         thread_unlock(td);
  647 
  648         return (rval);
  649 }
  650 
  651 /*
  652  * Block the current thread until it is awakened from its sleep queue,
  653  * it is interrupted by a signal, or it times out waiting to be awakened.
  654  */
  655 int
  656 sleepq_timedwait_sig(void *wchan, int pri)
  657 {
  658         int rcatch, rvalt, rvals;
  659 
  660         rcatch = sleepq_catch_signals(wchan, pri);
  661         rvalt = sleepq_check_timeout();
  662         rvals = sleepq_check_signals();
  663         thread_unlock(curthread);
  664         if (rcatch)
  665                 return (rcatch);
  666         if (rvals)
  667                 return (rvals);
  668         return (rvalt);
  669 }
  670 
  671 /*
  672  * Returns the type of sleepqueue given a waitchannel.
  673  */
  674 int
  675 sleepq_type(void *wchan)
  676 {
  677         struct sleepqueue *sq;
  678         int type;
  679 
  680         MPASS(wchan != NULL);
  681 
  682         sleepq_lock(wchan);
  683         sq = sleepq_lookup(wchan);
  684         if (sq == NULL) {
  685                 sleepq_release(wchan);
  686                 return (-1);
  687         }
  688         type = sq->sq_type;
  689         sleepq_release(wchan);
  690         return (type);
  691 }
  692 
  693 /*
  694  * Removes a thread from a sleep queue and makes it
  695  * runnable.
  696  */
  697 static int
  698 sleepq_resume_thread(struct sleepqueue *sq, struct thread *td, int pri)
  699 {
  700         struct sleepqueue_chain *sc;
  701 
  702         MPASS(td != NULL);
  703         MPASS(sq->sq_wchan != NULL);
  704         MPASS(td->td_wchan == sq->sq_wchan);
  705         MPASS(td->td_sqqueue < NR_SLEEPQS && td->td_sqqueue >= 0);
  706         THREAD_LOCK_ASSERT(td, MA_OWNED);
  707         sc = SC_LOOKUP(sq->sq_wchan);
  708         mtx_assert(&sc->sc_lock, MA_OWNED);
  709 
  710         /* Remove the thread from the queue. */
  711         sq->sq_blockedcnt[td->td_sqqueue]--;
  712         TAILQ_REMOVE(&sq->sq_blocked[td->td_sqqueue], td, td_slpq);
  713 
  714         /*
  715          * Get a sleep queue for this thread.  If this is the last waiter,
  716          * use the queue itself and take it out of the chain, otherwise,
  717          * remove a queue from the free list.
  718          */
  719         if (LIST_EMPTY(&sq->sq_free)) {
  720                 td->td_sleepqueue = sq;
  721 #ifdef INVARIANTS
  722                 sq->sq_wchan = NULL;
  723 #endif
  724 #ifdef SLEEPQUEUE_PROFILING
  725                 sc->sc_depth--;
  726 #endif
  727         } else
  728                 td->td_sleepqueue = LIST_FIRST(&sq->sq_free);
  729         LIST_REMOVE(td->td_sleepqueue, sq_hash);
  730 
  731         td->td_wmesg = NULL;
  732         td->td_wchan = NULL;
  733         td->td_flags &= ~(TDF_SINTR | TDF_SBDRY);
  734 
  735         CTR3(KTR_PROC, "sleepq_wakeup: thread %p (pid %ld, %s)",
  736             (void *)td, (long)td->td_proc->p_pid, td->td_name);
  737 
  738         /* Adjust priority if requested. */
  739         MPASS(pri == 0 || (pri >= PRI_MIN && pri <= PRI_MAX));
  740         if (pri != 0 && td->td_priority > pri)
  741                 sched_prio(td, pri);
  742 
  743         /*
  744          * Note that thread td might not be sleeping if it is running
  745          * sleepq_catch_signals() on another CPU or is blocked on its
  746          * proc lock to check signals.  There's no need to mark the
  747          * thread runnable in that case.
  748          */
  749         if (TD_IS_SLEEPING(td)) {
  750                 TD_CLR_SLEEPING(td);
  751                 return (setrunnable(td));
  752         }
  753         return (0);
  754 }
  755 
  756 #ifdef INVARIANTS
  757 /*
  758  * UMA zone item deallocator.
  759  */
  760 static void
  761 sleepq_dtor(void *mem, int size, void *arg)
  762 {
  763         struct sleepqueue *sq;
  764         int i;
  765 
  766         sq = mem;
  767         for (i = 0; i < NR_SLEEPQS; i++) {
  768                 MPASS(TAILQ_EMPTY(&sq->sq_blocked[i]));
  769                 MPASS(sq->sq_blockedcnt[i] == 0);
  770         }
  771 }
  772 #endif
  773 
  774 /*
  775  * UMA zone item initializer.
  776  */
  777 static int
  778 sleepq_init(void *mem, int size, int flags)
  779 {
  780         struct sleepqueue *sq;
  781         int i;
  782 
  783         bzero(mem, size);
  784         sq = mem;
  785         for (i = 0; i < NR_SLEEPQS; i++) {
  786                 TAILQ_INIT(&sq->sq_blocked[i]);
  787                 sq->sq_blockedcnt[i] = 0;
  788         }
  789         LIST_INIT(&sq->sq_free);
  790         return (0);
  791 }
  792 
  793 /*
  794  * Find the highest priority thread sleeping on a wait channel and resume it.
  795  */
  796 int
  797 sleepq_signal(void *wchan, int flags, int pri, int queue)
  798 {
  799         struct sleepqueue *sq;
  800         struct thread *td, *besttd;
  801         int wakeup_swapper;
  802 
  803         CTR2(KTR_PROC, "sleepq_signal(%p, %d)", wchan, flags);
  804         KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
  805         MPASS((queue >= 0) && (queue < NR_SLEEPQS));
  806         sq = sleepq_lookup(wchan);
  807         if (sq == NULL)
  808                 return (0);
  809         KASSERT(sq->sq_type == (flags & SLEEPQ_TYPE),
  810             ("%s: mismatch between sleep/wakeup and cv_*", __func__));
  811 
  812         /*
  813          * Find the highest priority thread on the queue.  If there is a
  814          * tie, use the thread that first appears in the queue as it has
  815          * been sleeping the longest since threads are always added to
  816          * the tail of sleep queues.
  817          */
  818         besttd = NULL;
  819         TAILQ_FOREACH(td, &sq->sq_blocked[queue], td_slpq) {
  820                 if (besttd == NULL || td->td_priority < besttd->td_priority)
  821                         besttd = td;
  822         }
  823         MPASS(besttd != NULL);
  824         thread_lock(besttd);
  825         wakeup_swapper = sleepq_resume_thread(sq, besttd, pri);
  826         thread_unlock(besttd);
  827         return (wakeup_swapper);
  828 }
  829 
  830 /*
  831  * Resume all threads sleeping on a specified wait channel.
  832  */
  833 int
  834 sleepq_broadcast(void *wchan, int flags, int pri, int queue)
  835 {
  836         struct sleepqueue *sq;
  837         struct thread *td, *tdn;
  838         int wakeup_swapper;
  839 
  840         CTR2(KTR_PROC, "sleepq_broadcast(%p, %d)", wchan, flags);
  841         KASSERT(wchan != NULL, ("%s: invalid NULL wait channel", __func__));
  842         MPASS((queue >= 0) && (queue < NR_SLEEPQS));
  843         sq = sleepq_lookup(wchan);
  844         if (sq == NULL)
  845                 return (0);
  846         KASSERT(sq->sq_type == (flags & SLEEPQ_TYPE),
  847             ("%s: mismatch between sleep/wakeup and cv_*", __func__));
  848 
  849         /* Resume all blocked threads on the sleep queue. */
  850         wakeup_swapper = 0;
  851         TAILQ_FOREACH_SAFE(td, &sq->sq_blocked[queue], td_slpq, tdn) {
  852                 thread_lock(td);
  853                 if (sleepq_resume_thread(sq, td, pri))
  854                         wakeup_swapper = 1;
  855                 thread_unlock(td);
  856         }
  857         return (wakeup_swapper);
  858 }
  859 
  860 /*
  861  * Time sleeping threads out.  When the timeout expires, the thread is
  862  * removed from the sleep queue and made runnable if it is still asleep.
  863  */
  864 static void
  865 sleepq_timeout(void *arg)
  866 {
  867         struct sleepqueue_chain *sc;
  868         struct sleepqueue *sq;
  869         struct thread *td;
  870         void *wchan;
  871         int wakeup_swapper;
  872 
  873         td = arg;
  874         wakeup_swapper = 0;
  875         CTR3(KTR_PROC, "sleepq_timeout: thread %p (pid %ld, %s)",
  876             (void *)td, (long)td->td_proc->p_pid, (void *)td->td_name);
  877 
  878         /*
  879          * First, see if the thread is asleep and get the wait channel if
  880          * it is.
  881          */
  882         thread_lock(td);
  883         if (TD_IS_SLEEPING(td) && TD_ON_SLEEPQ(td)) {
  884                 wchan = td->td_wchan;
  885                 sc = SC_LOOKUP(wchan);
  886                 THREAD_LOCKPTR_ASSERT(td, &sc->sc_lock);
  887                 sq = sleepq_lookup(wchan);
  888                 MPASS(sq != NULL);
  889                 td->td_flags |= TDF_TIMEOUT;
  890                 wakeup_swapper = sleepq_resume_thread(sq, td, 0);
  891                 thread_unlock(td);
  892                 if (wakeup_swapper)
  893                         kick_proc0();
  894                 return;
  895         }
  896 
  897         /*
  898          * If the thread is on the SLEEPQ but isn't sleeping yet, it
  899          * can either be on another CPU in between sleepq_add() and
  900          * one of the sleepq_*wait*() routines or it can be in
  901          * sleepq_catch_signals().
  902          */
  903         if (TD_ON_SLEEPQ(td)) {
  904                 td->td_flags |= TDF_TIMEOUT;
  905                 thread_unlock(td);
  906                 return;
  907         }
  908 
  909         /*
  910          * Now check for the edge cases.  First, if TDF_TIMEOUT is set,
  911          * then the other thread has already yielded to us, so clear
  912          * the flag and resume it.  If TDF_TIMEOUT is not set, then the
  913          * we know that the other thread is not on a sleep queue, but it
  914          * hasn't resumed execution yet.  In that case, set TDF_TIMOFAIL
  915          * to let it know that the timeout has already run and doesn't
  916          * need to be canceled.
  917          */
  918         if (td->td_flags & TDF_TIMEOUT) {
  919                 MPASS(TD_IS_SLEEPING(td));
  920                 td->td_flags &= ~TDF_TIMEOUT;
  921                 TD_CLR_SLEEPING(td);
  922                 wakeup_swapper = setrunnable(td);
  923         } else
  924                 td->td_flags |= TDF_TIMOFAIL;
  925         thread_unlock(td);
  926         if (wakeup_swapper)
  927                 kick_proc0();
  928 }
  929 
  930 /*
  931  * Resumes a specific thread from the sleep queue associated with a specific
  932  * wait channel if it is on that queue.
  933  */
  934 void
  935 sleepq_remove(struct thread *td, void *wchan)
  936 {
  937         struct sleepqueue *sq;
  938         int wakeup_swapper;
  939 
  940         /*
  941          * Look up the sleep queue for this wait channel, then re-check
  942          * that the thread is asleep on that channel, if it is not, then
  943          * bail.
  944          */
  945         MPASS(wchan != NULL);
  946         sleepq_lock(wchan);
  947         sq = sleepq_lookup(wchan);
  948         /*
  949          * We can not lock the thread here as it may be sleeping on a
  950          * different sleepq.  However, holding the sleepq lock for this
  951          * wchan can guarantee that we do not miss a wakeup for this
  952          * channel.  The asserts below will catch any false positives.
  953          */
  954         if (!TD_ON_SLEEPQ(td) || td->td_wchan != wchan) {
  955                 sleepq_release(wchan);
  956                 return;
  957         }
  958         /* Thread is asleep on sleep queue sq, so wake it up. */
  959         thread_lock(td);
  960         MPASS(sq != NULL);
  961         MPASS(td->td_wchan == wchan);
  962         wakeup_swapper = sleepq_resume_thread(sq, td, 0);
  963         thread_unlock(td);
  964         sleepq_release(wchan);
  965         if (wakeup_swapper)
  966                 kick_proc0();
  967 }
  968 
  969 /*
  970  * Abort a thread as if an interrupt had occurred.  Only abort
  971  * interruptible waits (unfortunately it isn't safe to abort others).
  972  */
  973 int
  974 sleepq_abort(struct thread *td, int intrval)
  975 {
  976         struct sleepqueue *sq;
  977         void *wchan;
  978 
  979         THREAD_LOCK_ASSERT(td, MA_OWNED);
  980         MPASS(TD_ON_SLEEPQ(td));
  981         MPASS(td->td_flags & TDF_SINTR);
  982         MPASS(intrval == EINTR || intrval == ERESTART);
  983 
  984         /*
  985          * If the TDF_TIMEOUT flag is set, just leave. A
  986          * timeout is scheduled anyhow.
  987          */
  988         if (td->td_flags & TDF_TIMEOUT)
  989                 return (0);
  990 
  991         CTR3(KTR_PROC, "sleepq_abort: thread %p (pid %ld, %s)",
  992             (void *)td, (long)td->td_proc->p_pid, (void *)td->td_name);
  993         td->td_intrval = intrval;
  994         td->td_flags |= TDF_SLEEPABORT;
  995         /*
  996          * If the thread has not slept yet it will find the signal in
  997          * sleepq_catch_signals() and call sleepq_resume_thread.  Otherwise
  998          * we have to do it here.
  999          */
 1000         if (!TD_IS_SLEEPING(td))
 1001                 return (0);
 1002         wchan = td->td_wchan;
 1003         MPASS(wchan != NULL);
 1004         sq = sleepq_lookup(wchan);
 1005         MPASS(sq != NULL);
 1006 
 1007         /* Thread is asleep on sleep queue sq, so wake it up. */
 1008         return (sleepq_resume_thread(sq, td, 0));
 1009 }
 1010 
 1011 #ifdef SLEEPQUEUE_PROFILING
 1012 #define SLEEPQ_PROF_LOCATIONS   1024
 1013 #define SLEEPQ_SBUFSIZE         (40 * 512)
 1014 struct sleepq_prof {
 1015         LIST_ENTRY(sleepq_prof) sp_link;
 1016         const char      *sp_wmesg;
 1017         long            sp_count;
 1018 };
 1019 
 1020 LIST_HEAD(sqphead, sleepq_prof);
 1021 
 1022 struct sqphead sleepq_prof_free;
 1023 struct sqphead sleepq_hash[SC_TABLESIZE];
 1024 static struct sleepq_prof sleepq_profent[SLEEPQ_PROF_LOCATIONS];
 1025 static struct mtx sleepq_prof_lock;
 1026 MTX_SYSINIT(sleepq_prof_lock, &sleepq_prof_lock, "sleepq_prof", MTX_SPIN);
 1027 
 1028 static void
 1029 sleepq_profile(const char *wmesg)
 1030 {
 1031         struct sleepq_prof *sp;
 1032 
 1033         mtx_lock_spin(&sleepq_prof_lock);
 1034         if (prof_enabled == 0)
 1035                 goto unlock;
 1036         LIST_FOREACH(sp, &sleepq_hash[SC_HASH(wmesg)], sp_link)
 1037                 if (sp->sp_wmesg == wmesg)
 1038                         goto done;
 1039         sp = LIST_FIRST(&sleepq_prof_free);
 1040         if (sp == NULL)
 1041                 goto unlock;
 1042         sp->sp_wmesg = wmesg;
 1043         LIST_REMOVE(sp, sp_link);
 1044         LIST_INSERT_HEAD(&sleepq_hash[SC_HASH(wmesg)], sp, sp_link);
 1045 done:
 1046         sp->sp_count++;
 1047 unlock:
 1048         mtx_unlock_spin(&sleepq_prof_lock);
 1049         return;
 1050 }
 1051 
 1052 static void
 1053 sleepq_prof_reset(void)
 1054 {
 1055         struct sleepq_prof *sp;
 1056         int enabled;
 1057         int i;
 1058 
 1059         mtx_lock_spin(&sleepq_prof_lock);
 1060         enabled = prof_enabled;
 1061         prof_enabled = 0;
 1062         for (i = 0; i < SC_TABLESIZE; i++)
 1063                 LIST_INIT(&sleepq_hash[i]);
 1064         LIST_INIT(&sleepq_prof_free);
 1065         for (i = 0; i < SLEEPQ_PROF_LOCATIONS; i++) {
 1066                 sp = &sleepq_profent[i];
 1067                 sp->sp_wmesg = NULL;
 1068                 sp->sp_count = 0;
 1069                 LIST_INSERT_HEAD(&sleepq_prof_free, sp, sp_link);
 1070         }
 1071         prof_enabled = enabled;
 1072         mtx_unlock_spin(&sleepq_prof_lock);
 1073 }
 1074 
 1075 static int
 1076 enable_sleepq_prof(SYSCTL_HANDLER_ARGS)
 1077 {
 1078         int error, v;
 1079 
 1080         v = prof_enabled;
 1081         error = sysctl_handle_int(oidp, &v, v, req);
 1082         if (error)
 1083                 return (error);
 1084         if (req->newptr == NULL)
 1085                 return (error);
 1086         if (v == prof_enabled)
 1087                 return (0);
 1088         if (v == 1)
 1089                 sleepq_prof_reset();
 1090         mtx_lock_spin(&sleepq_prof_lock);
 1091         prof_enabled = !!v;
 1092         mtx_unlock_spin(&sleepq_prof_lock);
 1093 
 1094         return (0);
 1095 }
 1096 
 1097 static int
 1098 reset_sleepq_prof_stats(SYSCTL_HANDLER_ARGS)
 1099 {
 1100         int error, v;
 1101 
 1102         v = 0;
 1103         error = sysctl_handle_int(oidp, &v, 0, req);
 1104         if (error)
 1105                 return (error);
 1106         if (req->newptr == NULL)
 1107                 return (error);
 1108         if (v == 0)
 1109                 return (0);
 1110         sleepq_prof_reset();
 1111 
 1112         return (0);
 1113 }
 1114 
 1115 static int
 1116 dump_sleepq_prof_stats(SYSCTL_HANDLER_ARGS)
 1117 {
 1118         static int multiplier = 1;
 1119         struct sleepq_prof *sp;
 1120         struct sbuf *sb;
 1121         int enabled;
 1122         int error;
 1123         int i;
 1124 
 1125 retry_sbufops:
 1126         sb = sbuf_new(NULL, NULL, SLEEPQ_SBUFSIZE * multiplier, SBUF_FIXEDLEN);
 1127         sbuf_printf(sb, "\nwmesg\tcount\n");
 1128         enabled = prof_enabled;
 1129         mtx_lock_spin(&sleepq_prof_lock);
 1130         prof_enabled = 0;
 1131         mtx_unlock_spin(&sleepq_prof_lock);
 1132         for (i = 0; i < SC_TABLESIZE; i++) {
 1133                 LIST_FOREACH(sp, &sleepq_hash[i], sp_link) {
 1134                         sbuf_printf(sb, "%s\t%ld\n",
 1135                             sp->sp_wmesg, sp->sp_count);
 1136                         if (sbuf_overflowed(sb)) {
 1137                                 sbuf_delete(sb);
 1138                                 multiplier++;
 1139                                 goto retry_sbufops;
 1140                         }
 1141                 }
 1142         }
 1143         mtx_lock_spin(&sleepq_prof_lock);
 1144         prof_enabled = enabled;
 1145         mtx_unlock_spin(&sleepq_prof_lock);
 1146 
 1147         sbuf_finish(sb);
 1148         error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1);
 1149         sbuf_delete(sb);
 1150         return (error);
 1151 }
 1152 
 1153 SYSCTL_PROC(_debug_sleepq, OID_AUTO, stats, CTLTYPE_STRING | CTLFLAG_RD,
 1154     NULL, 0, dump_sleepq_prof_stats, "A", "Sleepqueue profiling statistics");
 1155 SYSCTL_PROC(_debug_sleepq, OID_AUTO, reset, CTLTYPE_INT | CTLFLAG_RW,
 1156     NULL, 0, reset_sleepq_prof_stats, "I",
 1157     "Reset sleepqueue profiling statistics");
 1158 SYSCTL_PROC(_debug_sleepq, OID_AUTO, enable, CTLTYPE_INT | CTLFLAG_RW,
 1159     NULL, 0, enable_sleepq_prof, "I", "Enable sleepqueue profiling");
 1160 #endif
 1161 
 1162 #ifdef DDB
 1163 DB_SHOW_COMMAND(sleepq, db_show_sleepqueue)
 1164 {
 1165         struct sleepqueue_chain *sc;
 1166         struct sleepqueue *sq;
 1167 #ifdef INVARIANTS
 1168         struct lock_object *lock;
 1169 #endif
 1170         struct thread *td;
 1171         void *wchan;
 1172         int i;
 1173 
 1174         if (!have_addr)
 1175                 return;
 1176 
 1177         /*
 1178          * First, see if there is an active sleep queue for the wait channel
 1179          * indicated by the address.
 1180          */
 1181         wchan = (void *)addr;
 1182         sc = SC_LOOKUP(wchan);
 1183         LIST_FOREACH(sq, &sc->sc_queues, sq_hash)
 1184                 if (sq->sq_wchan == wchan)
 1185                         goto found;
 1186 
 1187         /*
 1188          * Second, see if there is an active sleep queue at the address
 1189          * indicated.
 1190          */
 1191         for (i = 0; i < SC_TABLESIZE; i++)
 1192                 LIST_FOREACH(sq, &sleepq_chains[i].sc_queues, sq_hash) {
 1193                         if (sq == (struct sleepqueue *)addr)
 1194                                 goto found;
 1195                 }
 1196 
 1197         db_printf("Unable to locate a sleep queue via %p\n", (void *)addr);
 1198         return;
 1199 found:
 1200         db_printf("Wait channel: %p\n", sq->sq_wchan);
 1201         db_printf("Queue type: %d\n", sq->sq_type);
 1202 #ifdef INVARIANTS
 1203         if (sq->sq_lock) {
 1204                 lock = sq->sq_lock;
 1205                 db_printf("Associated Interlock: %p - (%s) %s\n", lock,
 1206                     LOCK_CLASS(lock)->lc_name, lock->lo_name);
 1207         }
 1208 #endif
 1209         db_printf("Blocked threads:\n");
 1210         for (i = 0; i < NR_SLEEPQS; i++) {
 1211                 db_printf("\nQueue[%d]:\n", i);
 1212                 if (TAILQ_EMPTY(&sq->sq_blocked[i]))
 1213                         db_printf("\tempty\n");
 1214                 else
 1215                         TAILQ_FOREACH(td, &sq->sq_blocked[0],
 1216                                       td_slpq) {
 1217                                 db_printf("\t%p (tid %d, pid %d, \"%s\")\n", td,
 1218                                           td->td_tid, td->td_proc->p_pid,
 1219                                           td->td_name);
 1220                         }
 1221                 db_printf("(expected: %u)\n", sq->sq_blockedcnt[i]);
 1222         }
 1223 }
 1224 
 1225 /* Alias 'show sleepqueue' to 'show sleepq'. */
 1226 DB_SHOW_ALIAS(sleepqueue, db_show_sleepqueue);
 1227 #endif

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