The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]

FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_turnstile.c

Version: -  FREEBSD  -  FREEBSD-13-STABLE  -  FREEBSD-13-0  -  FREEBSD-12-STABLE  -  FREEBSD-12-0  -  FREEBSD-11-STABLE  -  FREEBSD-11-0  -  FREEBSD-10-STABLE  -  FREEBSD-10-0  -  FREEBSD-9-STABLE  -  FREEBSD-9-0  -  FREEBSD-8-STABLE  -  FREEBSD-8-0  -  FREEBSD-7-STABLE  -  FREEBSD-7-0  -  FREEBSD-6-STABLE  -  FREEBSD-6-0  -  FREEBSD-5-STABLE  -  FREEBSD-5-0  -  FREEBSD-4-STABLE  -  FREEBSD-3-STABLE  -  FREEBSD22  -  l41  -  OPENBSD  -  linux-2.6  -  MK84  -  PLAN9  -  xnu-8792 
SearchContext: -  none  -  3  -  10 

    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
    5  *
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice, this list of conditions and the following disclaimer.
   11  * 2. Redistributions in binary form must reproduce the above copyright
   12  *    notice, this list of conditions and the following disclaimer in the
   13  *    documentation and/or other materials provided with the distribution.
   14  * 3. Berkeley Software Design Inc's name may not be used to endorse or
   15  *    promote products derived from this software without specific prior
   16  *    written permission.
   17  *
   18  * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
   19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   21  * ARE DISCLAIMED.  IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
   22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   28  * SUCH DAMAGE.
   29  *
   30  *      from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
   31  *      and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
   32  */
   33 
   34 /*
   35  * Implementation of turnstiles used to hold queue of threads blocked on
   36  * non-sleepable locks.  Sleepable locks use condition variables to
   37  * implement their queues.  Turnstiles differ from a sleep queue in that
   38  * turnstile queue's are assigned to a lock held by an owning thread.  Thus,
   39  * when one thread is enqueued onto a turnstile, it can lend its priority
   40  * to the owning thread.
   41  *
   42  * We wish to avoid bloating locks with an embedded turnstile and we do not
   43  * want to use back-pointers in the locks for the same reason.  Thus, we
   44  * use a similar approach to that of Solaris 7 as described in Solaris
   45  * Internals by Jim Mauro and Richard McDougall.  Turnstiles are looked up
   46  * in a hash table based on the address of the lock.  Each entry in the
   47  * hash table is a linked-lists of turnstiles and is called a turnstile
   48  * chain.  Each chain contains a spin mutex that protects all of the
   49  * turnstiles in the chain.
   50  *
   51  * Each time a thread is created, a turnstile is allocated from a UMA zone
   52  * and attached to that thread.  When a thread blocks on a lock, if it is the
   53  * first thread to block, it lends its turnstile to the lock.  If the lock
   54  * already has a turnstile, then it gives its turnstile to the lock's
   55  * turnstile's free list.  When a thread is woken up, it takes a turnstile from
   56  * the free list if there are any other waiters.  If it is the only thread
   57  * blocked on the lock, then it reclaims the turnstile associated with the lock
   58  * and removes it from the hash table.
   59  */
   60 
   61 #include <sys/cdefs.h>
   62 __FBSDID("$FreeBSD$");
   63 
   64 #include "opt_ddb.h"
   65 #include "opt_turnstile_profiling.h"
   66 #include "opt_sched.h"
   67 
   68 #include <sys/param.h>
   69 #include <sys/systm.h>
   70 #include <sys/kdb.h>
   71 #include <sys/kernel.h>
   72 #include <sys/ktr.h>
   73 #include <sys/lock.h>
   74 #include <sys/mutex.h>
   75 #include <sys/proc.h>
   76 #include <sys/queue.h>
   77 #include <sys/sched.h>
   78 #include <sys/sdt.h>
   79 #include <sys/sysctl.h>
   80 #include <sys/turnstile.h>
   81 
   82 #include <vm/uma.h>
   83 
   84 #ifdef DDB
   85 #include <ddb/ddb.h>
   86 #include <sys/lockmgr.h>
   87 #include <sys/sx.h>
   88 #endif
   89 
   90 /*
   91  * Constants for the hash table of turnstile chains.  TC_SHIFT is a magic
   92  * number chosen because the sleep queue's use the same value for the
   93  * shift.  Basically, we ignore the lower 8 bits of the address.
   94  * TC_TABLESIZE must be a power of two for TC_MASK to work properly.
   95  */
   96 #define TC_TABLESIZE    128                     /* Must be power of 2. */
   97 #define TC_MASK         (TC_TABLESIZE - 1)
   98 #define TC_SHIFT        8
   99 #define TC_HASH(lock)   (((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK)
  100 #define TC_LOOKUP(lock) &turnstile_chains[TC_HASH(lock)]
  101 
  102 /*
  103  * There are three different lists of turnstiles as follows.  The list
  104  * connected by ts_link entries is a per-thread list of all the turnstiles
  105  * attached to locks that we own.  This is used to fixup our priority when
  106  * a lock is released.  The other two lists use the ts_hash entries.  The
  107  * first of these two is the turnstile chain list that a turnstile is on
  108  * when it is attached to a lock.  The second list to use ts_hash is the
  109  * free list hung off of a turnstile that is attached to a lock.
  110  *
  111  * Each turnstile contains three lists of threads.  The two ts_blocked lists
  112  * are linked list of threads blocked on the turnstile's lock.  One list is
  113  * for exclusive waiters, and the other is for shared waiters.  The
  114  * ts_pending list is a linked list of threads previously awakened by
  115  * turnstile_signal() or turnstile_wait() that are waiting to be put on
  116  * the run queue.
  117  *
  118  * Locking key:
  119  *  c - turnstile chain lock
  120  *  q - td_contested lock
  121  */
  122 struct turnstile {
  123         struct mtx ts_lock;                     /* Spin lock for self. */
  124         struct threadqueue ts_blocked[2];       /* (c + q) Blocked threads. */
  125         struct threadqueue ts_pending;          /* (c) Pending threads. */
  126         LIST_ENTRY(turnstile) ts_hash;          /* (c) Chain and free list. */
  127         LIST_ENTRY(turnstile) ts_link;          /* (q) Contested locks. */
  128         LIST_HEAD(, turnstile) ts_free;         /* (c) Free turnstiles. */
  129         struct lock_object *ts_lockobj;         /* (c) Lock we reference. */
  130         struct thread *ts_owner;                /* (c + q) Who owns the lock. */
  131 };
  132 
  133 struct turnstile_chain {
  134         LIST_HEAD(, turnstile) tc_turnstiles;   /* List of turnstiles. */
  135         struct mtx tc_lock;                     /* Spin lock for this chain. */
  136 #ifdef TURNSTILE_PROFILING
  137         u_int   tc_depth;                       /* Length of tc_queues. */
  138         u_int   tc_max_depth;                   /* Max length of tc_queues. */
  139 #endif
  140 };
  141 
  142 #ifdef TURNSTILE_PROFILING
  143 u_int turnstile_max_depth;
  144 static SYSCTL_NODE(_debug, OID_AUTO, turnstile, CTLFLAG_RD, 0,
  145     "turnstile profiling");
  146 static SYSCTL_NODE(_debug_turnstile, OID_AUTO, chains, CTLFLAG_RD, 0,
  147     "turnstile chain stats");
  148 SYSCTL_UINT(_debug_turnstile, OID_AUTO, max_depth, CTLFLAG_RD,
  149     &turnstile_max_depth, 0, "maximum depth achieved of a single chain");
  150 #endif
  151 static struct mtx td_contested_lock;
  152 static struct turnstile_chain turnstile_chains[TC_TABLESIZE];
  153 static uma_zone_t turnstile_zone;
  154 
  155 /*
  156  * Prototypes for non-exported routines.
  157  */
  158 static void     init_turnstile0(void *dummy);
  159 #ifdef TURNSTILE_PROFILING
  160 static void     init_turnstile_profiling(void *arg);
  161 #endif
  162 static void     propagate_priority(struct thread *td);
  163 static int      turnstile_adjust_thread(struct turnstile *ts,
  164                     struct thread *td);
  165 static struct thread *turnstile_first_waiter(struct turnstile *ts);
  166 static void     turnstile_setowner(struct turnstile *ts, struct thread *owner);
  167 #ifdef INVARIANTS
  168 static void     turnstile_dtor(void *mem, int size, void *arg);
  169 #endif
  170 static int      turnstile_init(void *mem, int size, int flags);
  171 static void     turnstile_fini(void *mem, int size);
  172 
  173 SDT_PROVIDER_DECLARE(sched);
  174 SDT_PROBE_DEFINE(sched, , , sleep);
  175 SDT_PROBE_DEFINE2(sched, , , wakeup, "struct thread *", 
  176     "struct proc *");
  177 
  178 /*
  179  * Walks the chain of turnstiles and their owners to propagate the priority
  180  * of the thread being blocked to all the threads holding locks that have to
  181  * release their locks before this thread can run again.
  182  */
  183 static void
  184 propagate_priority(struct thread *td)
  185 {
  186         struct turnstile *ts;
  187         int pri;
  188 
  189         THREAD_LOCK_ASSERT(td, MA_OWNED);
  190         pri = td->td_priority;
  191         ts = td->td_blocked;
  192         THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
  193         /*
  194          * Grab a recursive lock on this turnstile chain so it stays locked
  195          * for the whole operation.  The caller expects us to return with
  196          * the original lock held.  We only ever lock down the chain so
  197          * the lock order is constant.
  198          */
  199         mtx_lock_spin(&ts->ts_lock);
  200         for (;;) {
  201                 td = ts->ts_owner;
  202 
  203                 if (td == NULL) {
  204                         /*
  205                          * This might be a read lock with no owner.  There's
  206                          * not much we can do, so just bail.
  207                          */
  208                         mtx_unlock_spin(&ts->ts_lock);
  209                         return;
  210                 }
  211 
  212                 thread_lock_flags(td, MTX_DUPOK);
  213                 mtx_unlock_spin(&ts->ts_lock);
  214                 MPASS(td->td_proc != NULL);
  215                 MPASS(td->td_proc->p_magic == P_MAGIC);
  216 
  217                 /*
  218                  * If the thread is asleep, then we are probably about
  219                  * to deadlock.  To make debugging this easier, show
  220                  * backtrace of misbehaving thread and panic to not
  221                  * leave the kernel deadlocked.
  222                  */
  223                 if (TD_IS_SLEEPING(td)) {
  224                         printf(
  225                 "Sleeping thread (tid %d, pid %d) owns a non-sleepable lock\n",
  226                             td->td_tid, td->td_proc->p_pid);
  227                         kdb_backtrace_thread(td);
  228                         panic("sleeping thread");
  229                 }
  230 
  231                 /*
  232                  * If this thread already has higher priority than the
  233                  * thread that is being blocked, we are finished.
  234                  */
  235                 if (td->td_priority <= pri) {
  236                         thread_unlock(td);
  237                         return;
  238                 }
  239 
  240                 /*
  241                  * Bump this thread's priority.
  242                  */
  243                 sched_lend_prio(td, pri);
  244 
  245                 /*
  246                  * If lock holder is actually running or on the run queue
  247                  * then we are done.
  248                  */
  249                 if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) {
  250                         MPASS(td->td_blocked == NULL);
  251                         thread_unlock(td);
  252                         return;
  253                 }
  254 
  255 #ifndef SMP
  256                 /*
  257                  * For UP, we check to see if td is curthread (this shouldn't
  258                  * ever happen however as it would mean we are in a deadlock.)
  259                  */
  260                 KASSERT(td != curthread, ("Deadlock detected"));
  261 #endif
  262 
  263                 /*
  264                  * If we aren't blocked on a lock, we should be.
  265                  */
  266                 KASSERT(TD_ON_LOCK(td), (
  267                     "thread %d(%s):%d holds %s but isn't blocked on a lock\n",
  268                     td->td_tid, td->td_name, td->td_state,
  269                     ts->ts_lockobj->lo_name));
  270 
  271                 /*
  272                  * Pick up the lock that td is blocked on.
  273                  */
  274                 ts = td->td_blocked;
  275                 MPASS(ts != NULL);
  276                 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
  277                 /* Resort td on the list if needed. */
  278                 if (!turnstile_adjust_thread(ts, td)) {
  279                         mtx_unlock_spin(&ts->ts_lock);
  280                         return;
  281                 }
  282                 /* The thread lock is released as ts lock above. */
  283         }
  284 }
  285 
  286 /*
  287  * Adjust the thread's position on a turnstile after its priority has been
  288  * changed.
  289  */
  290 static int
  291 turnstile_adjust_thread(struct turnstile *ts, struct thread *td)
  292 {
  293         struct thread *td1, *td2;
  294         int queue;
  295 
  296         THREAD_LOCK_ASSERT(td, MA_OWNED);
  297         MPASS(TD_ON_LOCK(td));
  298 
  299         /*
  300          * This thread may not be blocked on this turnstile anymore
  301          * but instead might already be woken up on another CPU
  302          * that is waiting on the thread lock in turnstile_unpend() to
  303          * finish waking this thread up.  We can detect this case
  304          * by checking to see if this thread has been given a
  305          * turnstile by either turnstile_signal() or
  306          * turnstile_broadcast().  In this case, treat the thread as
  307          * if it was already running.
  308          */
  309         if (td->td_turnstile != NULL)
  310                 return (0);
  311 
  312         /*
  313          * Check if the thread needs to be moved on the blocked chain.
  314          * It needs to be moved if either its priority is lower than
  315          * the previous thread or higher than the next thread.
  316          */
  317         THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
  318         td1 = TAILQ_PREV(td, threadqueue, td_lockq);
  319         td2 = TAILQ_NEXT(td, td_lockq);
  320         if ((td1 != NULL && td->td_priority < td1->td_priority) ||
  321             (td2 != NULL && td->td_priority > td2->td_priority)) {
  322 
  323                 /*
  324                  * Remove thread from blocked chain and determine where
  325                  * it should be moved to.
  326                  */
  327                 queue = td->td_tsqueue;
  328                 MPASS(queue == TS_EXCLUSIVE_QUEUE || queue == TS_SHARED_QUEUE);
  329                 mtx_lock_spin(&td_contested_lock);
  330                 TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq);
  331                 TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq) {
  332                         MPASS(td1->td_proc->p_magic == P_MAGIC);
  333                         if (td1->td_priority > td->td_priority)
  334                                 break;
  335                 }
  336 
  337                 if (td1 == NULL)
  338                         TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
  339                 else
  340                         TAILQ_INSERT_BEFORE(td1, td, td_lockq);
  341                 mtx_unlock_spin(&td_contested_lock);
  342                 if (td1 == NULL)
  343                         CTR3(KTR_LOCK,
  344                     "turnstile_adjust_thread: td %d put at tail on [%p] %s",
  345                             td->td_tid, ts->ts_lockobj, ts->ts_lockobj->lo_name);
  346                 else
  347                         CTR4(KTR_LOCK,
  348                     "turnstile_adjust_thread: td %d moved before %d on [%p] %s",
  349                             td->td_tid, td1->td_tid, ts->ts_lockobj,
  350                             ts->ts_lockobj->lo_name);
  351         }
  352         return (1);
  353 }
  354 
  355 /*
  356  * Early initialization of turnstiles.  This is not done via a SYSINIT()
  357  * since this needs to be initialized very early when mutexes are first
  358  * initialized.
  359  */
  360 void
  361 init_turnstiles(void)
  362 {
  363         int i;
  364 
  365         for (i = 0; i < TC_TABLESIZE; i++) {
  366                 LIST_INIT(&turnstile_chains[i].tc_turnstiles);
  367                 mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain",
  368                     NULL, MTX_SPIN);
  369         }
  370         mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN);
  371         LIST_INIT(&thread0.td_contested);
  372         thread0.td_turnstile = NULL;
  373 }
  374 
  375 #ifdef TURNSTILE_PROFILING
  376 static void
  377 init_turnstile_profiling(void *arg)
  378 {
  379         struct sysctl_oid *chain_oid;
  380         char chain_name[10];
  381         int i;
  382 
  383         for (i = 0; i < TC_TABLESIZE; i++) {
  384                 snprintf(chain_name, sizeof(chain_name), "%d", i);
  385                 chain_oid = SYSCTL_ADD_NODE(NULL, 
  386                     SYSCTL_STATIC_CHILDREN(_debug_turnstile_chains), OID_AUTO,
  387                     chain_name, CTLFLAG_RD, NULL, "turnstile chain stats");
  388                 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
  389                     "depth", CTLFLAG_RD, &turnstile_chains[i].tc_depth, 0,
  390                     NULL);
  391                 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
  392                     "max_depth", CTLFLAG_RD, &turnstile_chains[i].tc_max_depth,
  393                     0, NULL);
  394         }
  395 }
  396 SYSINIT(turnstile_profiling, SI_SUB_LOCK, SI_ORDER_ANY,
  397     init_turnstile_profiling, NULL);
  398 #endif
  399 
  400 static void
  401 init_turnstile0(void *dummy)
  402 {
  403 
  404         turnstile_zone = uma_zcreate("TURNSTILE", sizeof(struct turnstile),
  405             NULL,
  406 #ifdef INVARIANTS
  407             turnstile_dtor,
  408 #else
  409             NULL,
  410 #endif
  411             turnstile_init, turnstile_fini, UMA_ALIGN_CACHE, UMA_ZONE_NOFREE);
  412         thread0.td_turnstile = turnstile_alloc();
  413 }
  414 SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL);
  415 
  416 /*
  417  * Update a thread on the turnstile list after it's priority has been changed.
  418  * The old priority is passed in as an argument.
  419  */
  420 void
  421 turnstile_adjust(struct thread *td, u_char oldpri)
  422 {
  423         struct turnstile *ts;
  424 
  425         MPASS(TD_ON_LOCK(td));
  426 
  427         /*
  428          * Pick up the lock that td is blocked on.
  429          */
  430         ts = td->td_blocked;
  431         MPASS(ts != NULL);
  432         THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
  433         mtx_assert(&ts->ts_lock, MA_OWNED);
  434 
  435         /* Resort the turnstile on the list. */
  436         if (!turnstile_adjust_thread(ts, td))
  437                 return;
  438         /*
  439          * If our priority was lowered and we are at the head of the
  440          * turnstile, then propagate our new priority up the chain.
  441          * Note that we currently don't try to revoke lent priorities
  442          * when our priority goes up.
  443          */
  444         MPASS(td->td_tsqueue == TS_EXCLUSIVE_QUEUE ||
  445             td->td_tsqueue == TS_SHARED_QUEUE);
  446         if (td == TAILQ_FIRST(&ts->ts_blocked[td->td_tsqueue]) &&
  447             td->td_priority < oldpri) {
  448                 propagate_priority(td);
  449         }
  450 }
  451 
  452 /*
  453  * Set the owner of the lock this turnstile is attached to.
  454  */
  455 static void
  456 turnstile_setowner(struct turnstile *ts, struct thread *owner)
  457 {
  458 
  459         mtx_assert(&td_contested_lock, MA_OWNED);
  460         MPASS(ts->ts_owner == NULL);
  461 
  462         /* A shared lock might not have an owner. */
  463         if (owner == NULL)
  464                 return;
  465 
  466         MPASS(owner->td_proc->p_magic == P_MAGIC);
  467         ts->ts_owner = owner;
  468         LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link);
  469 }
  470 
  471 #ifdef INVARIANTS
  472 /*
  473  * UMA zone item deallocator.
  474  */
  475 static void
  476 turnstile_dtor(void *mem, int size, void *arg)
  477 {
  478         struct turnstile *ts;
  479 
  480         ts = mem;
  481         MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]));
  482         MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]));
  483         MPASS(TAILQ_EMPTY(&ts->ts_pending));
  484 }
  485 #endif
  486 
  487 /*
  488  * UMA zone item initializer.
  489  */
  490 static int
  491 turnstile_init(void *mem, int size, int flags)
  492 {
  493         struct turnstile *ts;
  494 
  495         bzero(mem, size);
  496         ts = mem;
  497         TAILQ_INIT(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]);
  498         TAILQ_INIT(&ts->ts_blocked[TS_SHARED_QUEUE]);
  499         TAILQ_INIT(&ts->ts_pending);
  500         LIST_INIT(&ts->ts_free);
  501         mtx_init(&ts->ts_lock, "turnstile lock", NULL, MTX_SPIN | MTX_RECURSE);
  502         return (0);
  503 }
  504 
  505 static void
  506 turnstile_fini(void *mem, int size)
  507 {
  508         struct turnstile *ts;
  509 
  510         ts = mem;
  511         mtx_destroy(&ts->ts_lock);
  512 }
  513 
  514 /*
  515  * Get a turnstile for a new thread.
  516  */
  517 struct turnstile *
  518 turnstile_alloc(void)
  519 {
  520 
  521         return (uma_zalloc(turnstile_zone, M_WAITOK));
  522 }
  523 
  524 /*
  525  * Free a turnstile when a thread is destroyed.
  526  */
  527 void
  528 turnstile_free(struct turnstile *ts)
  529 {
  530 
  531         uma_zfree(turnstile_zone, ts);
  532 }
  533 
  534 /*
  535  * Lock the turnstile chain associated with the specified lock.
  536  */
  537 void
  538 turnstile_chain_lock(struct lock_object *lock)
  539 {
  540         struct turnstile_chain *tc;
  541 
  542         tc = TC_LOOKUP(lock);
  543         mtx_lock_spin(&tc->tc_lock);
  544 }
  545 
  546 struct turnstile *
  547 turnstile_trywait(struct lock_object *lock)
  548 {
  549         struct turnstile_chain *tc;
  550         struct turnstile *ts;
  551 
  552         tc = TC_LOOKUP(lock);
  553         mtx_lock_spin(&tc->tc_lock);
  554         LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
  555                 if (ts->ts_lockobj == lock) {
  556                         mtx_lock_spin(&ts->ts_lock);
  557                         return (ts);
  558                 }
  559 
  560         ts = curthread->td_turnstile;
  561         MPASS(ts != NULL);
  562         mtx_lock_spin(&ts->ts_lock);
  563         KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer"));
  564         ts->ts_lockobj = lock;
  565 
  566         return (ts);
  567 }
  568 
  569 bool
  570 turnstile_lock(struct turnstile *ts, struct lock_object **lockp,
  571     struct thread **tdp)
  572 {
  573         struct turnstile_chain *tc;
  574         struct lock_object *lock;
  575 
  576         if ((lock = ts->ts_lockobj) == NULL)
  577                 return (false);
  578         tc = TC_LOOKUP(lock);
  579         mtx_lock_spin(&tc->tc_lock);
  580         mtx_lock_spin(&ts->ts_lock);
  581         if (__predict_false(lock != ts->ts_lockobj)) {
  582                 mtx_unlock_spin(&tc->tc_lock);
  583                 mtx_unlock_spin(&ts->ts_lock);
  584                 return (false);
  585         }
  586         *lockp = lock;
  587         *tdp = ts->ts_owner;
  588         return (true);
  589 }
  590 
  591 void
  592 turnstile_unlock(struct turnstile *ts, struct lock_object *lock)
  593 {
  594         struct turnstile_chain *tc;
  595 
  596         mtx_assert(&ts->ts_lock, MA_OWNED);
  597         mtx_unlock_spin(&ts->ts_lock);
  598         if (ts == curthread->td_turnstile)
  599                 ts->ts_lockobj = NULL;
  600         tc = TC_LOOKUP(lock);
  601         mtx_unlock_spin(&tc->tc_lock);
  602 }
  603 
  604 void
  605 turnstile_assert(struct turnstile *ts)
  606 {
  607         MPASS(ts->ts_lockobj == NULL);
  608 }
  609 
  610 void
  611 turnstile_cancel(struct turnstile *ts)
  612 {
  613         struct turnstile_chain *tc;
  614         struct lock_object *lock;
  615 
  616         mtx_assert(&ts->ts_lock, MA_OWNED);
  617 
  618         mtx_unlock_spin(&ts->ts_lock);
  619         lock = ts->ts_lockobj;
  620         if (ts == curthread->td_turnstile)
  621                 ts->ts_lockobj = NULL;
  622         tc = TC_LOOKUP(lock);
  623         mtx_unlock_spin(&tc->tc_lock);
  624 }
  625 
  626 /*
  627  * Look up the turnstile for a lock in the hash table locking the associated
  628  * turnstile chain along the way.  If no turnstile is found in the hash
  629  * table, NULL is returned.
  630  */
  631 struct turnstile *
  632 turnstile_lookup(struct lock_object *lock)
  633 {
  634         struct turnstile_chain *tc;
  635         struct turnstile *ts;
  636 
  637         tc = TC_LOOKUP(lock);
  638         mtx_assert(&tc->tc_lock, MA_OWNED);
  639         LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
  640                 if (ts->ts_lockobj == lock) {
  641                         mtx_lock_spin(&ts->ts_lock);
  642                         return (ts);
  643                 }
  644         return (NULL);
  645 }
  646 
  647 /*
  648  * Unlock the turnstile chain associated with a given lock.
  649  */
  650 void
  651 turnstile_chain_unlock(struct lock_object *lock)
  652 {
  653         struct turnstile_chain *tc;
  654 
  655         tc = TC_LOOKUP(lock);
  656         mtx_unlock_spin(&tc->tc_lock);
  657 }
  658 
  659 /*
  660  * Return a pointer to the thread waiting on this turnstile with the
  661  * most important priority or NULL if the turnstile has no waiters.
  662  */
  663 static struct thread *
  664 turnstile_first_waiter(struct turnstile *ts)
  665 {
  666         struct thread *std, *xtd;
  667 
  668         std = TAILQ_FIRST(&ts->ts_blocked[TS_SHARED_QUEUE]);
  669         xtd = TAILQ_FIRST(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]);
  670         if (xtd == NULL || (std != NULL && std->td_priority < xtd->td_priority))
  671                 return (std);
  672         return (xtd);
  673 }
  674 
  675 /*
  676  * Take ownership of a turnstile and adjust the priority of the new
  677  * owner appropriately.
  678  */
  679 void
  680 turnstile_claim(struct turnstile *ts)
  681 {
  682         struct thread *td, *owner;
  683         struct turnstile_chain *tc;
  684 
  685         mtx_assert(&ts->ts_lock, MA_OWNED);
  686         MPASS(ts != curthread->td_turnstile);
  687 
  688         owner = curthread;
  689         mtx_lock_spin(&td_contested_lock);
  690         turnstile_setowner(ts, owner);
  691         mtx_unlock_spin(&td_contested_lock);
  692 
  693         td = turnstile_first_waiter(ts);
  694         MPASS(td != NULL);
  695         MPASS(td->td_proc->p_magic == P_MAGIC);
  696         THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
  697 
  698         /*
  699          * Update the priority of the new owner if needed.
  700          */
  701         thread_lock(owner);
  702         if (td->td_priority < owner->td_priority)
  703                 sched_lend_prio(owner, td->td_priority);
  704         thread_unlock(owner);
  705         tc = TC_LOOKUP(ts->ts_lockobj);
  706         mtx_unlock_spin(&ts->ts_lock);
  707         mtx_unlock_spin(&tc->tc_lock);
  708 }
  709 
  710 /*
  711  * Block the current thread on the turnstile assicated with 'lock'.  This
  712  * function will context switch and not return until this thread has been
  713  * woken back up.  This function must be called with the appropriate
  714  * turnstile chain locked and will return with it unlocked.
  715  */
  716 void
  717 turnstile_wait(struct turnstile *ts, struct thread *owner, int queue)
  718 {
  719         struct turnstile_chain *tc;
  720         struct thread *td, *td1;
  721         struct lock_object *lock;
  722 
  723         td = curthread;
  724         mtx_assert(&ts->ts_lock, MA_OWNED);
  725         if (owner)
  726                 MPASS(owner->td_proc->p_magic == P_MAGIC);
  727         MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
  728 
  729         /*
  730          * If the lock does not already have a turnstile, use this thread's
  731          * turnstile.  Otherwise insert the current thread into the
  732          * turnstile already in use by this lock.
  733          */
  734         tc = TC_LOOKUP(ts->ts_lockobj);
  735         mtx_assert(&tc->tc_lock, MA_OWNED);
  736         if (ts == td->td_turnstile) {
  737 #ifdef TURNSTILE_PROFILING
  738                 tc->tc_depth++;
  739                 if (tc->tc_depth > tc->tc_max_depth) {
  740                         tc->tc_max_depth = tc->tc_depth;
  741                         if (tc->tc_max_depth > turnstile_max_depth)
  742                                 turnstile_max_depth = tc->tc_max_depth;
  743                 }
  744 #endif
  745                 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash);
  746                 KASSERT(TAILQ_EMPTY(&ts->ts_pending),
  747                     ("thread's turnstile has pending threads"));
  748                 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]),
  749                     ("thread's turnstile has exclusive waiters"));
  750                 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]),
  751                     ("thread's turnstile has shared waiters"));
  752                 KASSERT(LIST_EMPTY(&ts->ts_free),
  753                     ("thread's turnstile has a non-empty free list"));
  754                 MPASS(ts->ts_lockobj != NULL);
  755                 mtx_lock_spin(&td_contested_lock);
  756                 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
  757                 turnstile_setowner(ts, owner);
  758                 mtx_unlock_spin(&td_contested_lock);
  759         } else {
  760                 TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq)
  761                         if (td1->td_priority > td->td_priority)
  762                                 break;
  763                 mtx_lock_spin(&td_contested_lock);
  764                 if (td1 != NULL)
  765                         TAILQ_INSERT_BEFORE(td1, td, td_lockq);
  766                 else
  767                         TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
  768                 MPASS(owner == ts->ts_owner);
  769                 mtx_unlock_spin(&td_contested_lock);
  770                 MPASS(td->td_turnstile != NULL);
  771                 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash);
  772         }
  773         thread_lock(td);
  774         thread_lock_set(td, &ts->ts_lock);
  775         td->td_turnstile = NULL;
  776 
  777         /* Save who we are blocked on and switch. */
  778         lock = ts->ts_lockobj;
  779         td->td_tsqueue = queue;
  780         td->td_blocked = ts;
  781         td->td_lockname = lock->lo_name;
  782         td->td_blktick = ticks;
  783         TD_SET_LOCK(td);
  784         mtx_unlock_spin(&tc->tc_lock);
  785         propagate_priority(td);
  786 
  787         if (LOCK_LOG_TEST(lock, 0))
  788                 CTR4(KTR_LOCK, "%s: td %d blocked on [%p] %s", __func__,
  789                     td->td_tid, lock, lock->lo_name);
  790 
  791         SDT_PROBE0(sched, , , sleep);
  792 
  793         THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
  794         mi_switch(SW_VOL | SWT_TURNSTILE, NULL);
  795 
  796         if (LOCK_LOG_TEST(lock, 0))
  797                 CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s",
  798                     __func__, td->td_tid, lock, lock->lo_name);
  799         thread_unlock(td);
  800 }
  801 
  802 /*
  803  * Pick the highest priority thread on this turnstile and put it on the
  804  * pending list.  This must be called with the turnstile chain locked.
  805  */
  806 int
  807 turnstile_signal(struct turnstile *ts, int queue)
  808 {
  809         struct turnstile_chain *tc __unused;
  810         struct thread *td;
  811         int empty;
  812 
  813         MPASS(ts != NULL);
  814         mtx_assert(&ts->ts_lock, MA_OWNED);
  815         MPASS(curthread->td_proc->p_magic == P_MAGIC);
  816         MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL);
  817         MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
  818 
  819         /*
  820          * Pick the highest priority thread blocked on this lock and
  821          * move it to the pending list.
  822          */
  823         td = TAILQ_FIRST(&ts->ts_blocked[queue]);
  824         MPASS(td->td_proc->p_magic == P_MAGIC);
  825         mtx_lock_spin(&td_contested_lock);
  826         TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq);
  827         mtx_unlock_spin(&td_contested_lock);
  828         TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq);
  829 
  830         /*
  831          * If the turnstile is now empty, remove it from its chain and
  832          * give it to the about-to-be-woken thread.  Otherwise take a
  833          * turnstile from the free list and give it to the thread.
  834          */
  835         empty = TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) &&
  836             TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]);
  837         if (empty) {
  838                 tc = TC_LOOKUP(ts->ts_lockobj);
  839                 mtx_assert(&tc->tc_lock, MA_OWNED);
  840                 MPASS(LIST_EMPTY(&ts->ts_free));
  841 #ifdef TURNSTILE_PROFILING
  842                 tc->tc_depth--;
  843 #endif
  844         } else
  845                 ts = LIST_FIRST(&ts->ts_free);
  846         MPASS(ts != NULL);
  847         LIST_REMOVE(ts, ts_hash);
  848         td->td_turnstile = ts;
  849 
  850         return (empty);
  851 }
  852         
  853 /*
  854  * Put all blocked threads on the pending list.  This must be called with
  855  * the turnstile chain locked.
  856  */
  857 void
  858 turnstile_broadcast(struct turnstile *ts, int queue)
  859 {
  860         struct turnstile_chain *tc __unused;
  861         struct turnstile *ts1;
  862         struct thread *td;
  863 
  864         MPASS(ts != NULL);
  865         mtx_assert(&ts->ts_lock, MA_OWNED);
  866         MPASS(curthread->td_proc->p_magic == P_MAGIC);
  867         MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL);
  868         /*
  869          * We must have the chain locked so that we can remove the empty
  870          * turnstile from the hash queue.
  871          */
  872         tc = TC_LOOKUP(ts->ts_lockobj);
  873         mtx_assert(&tc->tc_lock, MA_OWNED);
  874         MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
  875 
  876         /*
  877          * Transfer the blocked list to the pending list.
  878          */
  879         mtx_lock_spin(&td_contested_lock);
  880         TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked[queue], td_lockq);
  881         mtx_unlock_spin(&td_contested_lock);
  882 
  883         /*
  884          * Give a turnstile to each thread.  The last thread gets
  885          * this turnstile if the turnstile is empty.
  886          */
  887         TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) {
  888                 if (LIST_EMPTY(&ts->ts_free)) {
  889                         MPASS(TAILQ_NEXT(td, td_lockq) == NULL);
  890                         ts1 = ts;
  891 #ifdef TURNSTILE_PROFILING
  892                         tc->tc_depth--;
  893 #endif
  894                 } else
  895                         ts1 = LIST_FIRST(&ts->ts_free);
  896                 MPASS(ts1 != NULL);
  897                 LIST_REMOVE(ts1, ts_hash);
  898                 td->td_turnstile = ts1;
  899         }
  900 }
  901 
  902 static u_char
  903 turnstile_calc_unlend_prio_locked(struct thread *td)
  904 {
  905         struct turnstile *nts;
  906         u_char cp, pri;
  907 
  908         THREAD_LOCK_ASSERT(td, MA_OWNED);
  909         mtx_assert(&td_contested_lock, MA_OWNED);
  910 
  911         pri = PRI_MAX;
  912         LIST_FOREACH(nts, &td->td_contested, ts_link) {
  913                 cp = turnstile_first_waiter(nts)->td_priority;
  914                 if (cp < pri)
  915                         pri = cp;
  916         }
  917         return (pri);
  918 }
  919 
  920 /*
  921  * Wakeup all threads on the pending list and adjust the priority of the
  922  * current thread appropriately.  This must be called with the turnstile
  923  * chain locked.
  924  */
  925 void
  926 turnstile_unpend(struct turnstile *ts)
  927 {
  928         TAILQ_HEAD( ,thread) pending_threads;
  929         struct thread *td;
  930         u_char pri;
  931 
  932         MPASS(ts != NULL);
  933         mtx_assert(&ts->ts_lock, MA_OWNED);
  934         MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL);
  935         MPASS(!TAILQ_EMPTY(&ts->ts_pending));
  936 
  937         /*
  938          * Move the list of pending threads out of the turnstile and
  939          * into a local variable.
  940          */
  941         TAILQ_INIT(&pending_threads);
  942         TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq);
  943 #ifdef INVARIANTS
  944         if (TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) &&
  945             TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]))
  946                 ts->ts_lockobj = NULL;
  947 #endif
  948         /*
  949          * Adjust the priority of curthread based on other contested
  950          * locks it owns.  Don't lower the priority below the base
  951          * priority however.
  952          */
  953         td = curthread;
  954         thread_lock(td);
  955         mtx_lock_spin(&td_contested_lock);
  956         /*
  957          * Remove the turnstile from this thread's list of contested locks
  958          * since this thread doesn't own it anymore.  New threads will
  959          * not be blocking on the turnstile until it is claimed by a new
  960          * owner.  There might not be a current owner if this is a shared
  961          * lock.
  962          */
  963         if (ts->ts_owner != NULL) {
  964                 ts->ts_owner = NULL;
  965                 LIST_REMOVE(ts, ts_link);
  966         }
  967         pri = turnstile_calc_unlend_prio_locked(td);
  968         mtx_unlock_spin(&td_contested_lock);
  969         sched_unlend_prio(td, pri);
  970         thread_unlock(td);
  971         /*
  972          * Wake up all the pending threads.  If a thread is not blocked
  973          * on a lock, then it is currently executing on another CPU in
  974          * turnstile_wait() or sitting on a run queue waiting to resume
  975          * in turnstile_wait().  Set a flag to force it to try to acquire
  976          * the lock again instead of blocking.
  977          */
  978         while (!TAILQ_EMPTY(&pending_threads)) {
  979                 td = TAILQ_FIRST(&pending_threads);
  980                 TAILQ_REMOVE(&pending_threads, td, td_lockq);
  981                 SDT_PROBE2(sched, , , wakeup, td, td->td_proc);
  982                 thread_lock(td);
  983                 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock);
  984                 MPASS(td->td_proc->p_magic == P_MAGIC);
  985                 MPASS(TD_ON_LOCK(td));
  986                 TD_CLR_LOCK(td);
  987                 MPASS(TD_CAN_RUN(td));
  988                 td->td_blocked = NULL;
  989                 td->td_lockname = NULL;
  990                 td->td_blktick = 0;
  991 #ifdef INVARIANTS
  992                 td->td_tsqueue = 0xff;
  993 #endif
  994                 sched_add(td, SRQ_BORING);
  995                 thread_unlock(td);
  996         }
  997         mtx_unlock_spin(&ts->ts_lock);
  998 }
  999 
 1000 /*
 1001  * Give up ownership of a turnstile.  This must be called with the
 1002  * turnstile chain locked.
 1003  */
 1004 void
 1005 turnstile_disown(struct turnstile *ts)
 1006 {
 1007         struct thread *td;
 1008         u_char pri;
 1009 
 1010         MPASS(ts != NULL);
 1011         mtx_assert(&ts->ts_lock, MA_OWNED);
 1012         MPASS(ts->ts_owner == curthread);
 1013         MPASS(TAILQ_EMPTY(&ts->ts_pending));
 1014         MPASS(!TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) ||
 1015             !TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]));
 1016 
 1017         /*
 1018          * Remove the turnstile from this thread's list of contested locks
 1019          * since this thread doesn't own it anymore.  New threads will
 1020          * not be blocking on the turnstile until it is claimed by a new
 1021          * owner.
 1022          */
 1023         mtx_lock_spin(&td_contested_lock);
 1024         ts->ts_owner = NULL;
 1025         LIST_REMOVE(ts, ts_link);
 1026         mtx_unlock_spin(&td_contested_lock);
 1027 
 1028         /*
 1029          * Adjust the priority of curthread based on other contested
 1030          * locks it owns.  Don't lower the priority below the base
 1031          * priority however.
 1032          */
 1033         td = curthread;
 1034         thread_lock(td);
 1035         mtx_unlock_spin(&ts->ts_lock);
 1036         mtx_lock_spin(&td_contested_lock);
 1037         pri = turnstile_calc_unlend_prio_locked(td);
 1038         mtx_unlock_spin(&td_contested_lock);
 1039         sched_unlend_prio(td, pri);
 1040         thread_unlock(td);
 1041 }
 1042 
 1043 /*
 1044  * Return the first thread in a turnstile.
 1045  */
 1046 struct thread *
 1047 turnstile_head(struct turnstile *ts, int queue)
 1048 {
 1049 #ifdef INVARIANTS
 1050 
 1051         MPASS(ts != NULL);
 1052         MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
 1053         mtx_assert(&ts->ts_lock, MA_OWNED);
 1054 #endif
 1055         return (TAILQ_FIRST(&ts->ts_blocked[queue]));
 1056 }
 1057 
 1058 /*
 1059  * Returns true if a sub-queue of a turnstile is empty.
 1060  */
 1061 int
 1062 turnstile_empty(struct turnstile *ts, int queue)
 1063 {
 1064 #ifdef INVARIANTS
 1065 
 1066         MPASS(ts != NULL);
 1067         MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
 1068         mtx_assert(&ts->ts_lock, MA_OWNED);
 1069 #endif
 1070         return (TAILQ_EMPTY(&ts->ts_blocked[queue]));
 1071 }
 1072 
 1073 #ifdef DDB
 1074 static void
 1075 print_thread(struct thread *td, const char *prefix)
 1076 {
 1077 
 1078         db_printf("%s%p (tid %d, pid %d, \"%s\")\n", prefix, td, td->td_tid,
 1079             td->td_proc->p_pid, td->td_name);
 1080 }
 1081 
 1082 static void
 1083 print_queue(struct threadqueue *queue, const char *header, const char *prefix)
 1084 {
 1085         struct thread *td;
 1086 
 1087         db_printf("%s:\n", header);
 1088         if (TAILQ_EMPTY(queue)) {
 1089                 db_printf("%sempty\n", prefix);
 1090                 return;
 1091         }
 1092         TAILQ_FOREACH(td, queue, td_lockq) {
 1093                 print_thread(td, prefix);
 1094         }
 1095 }
 1096 
 1097 DB_SHOW_COMMAND(turnstile, db_show_turnstile)
 1098 {
 1099         struct turnstile_chain *tc;
 1100         struct turnstile *ts;
 1101         struct lock_object *lock;
 1102         int i;
 1103 
 1104         if (!have_addr)
 1105                 return;
 1106 
 1107         /*
 1108          * First, see if there is an active turnstile for the lock indicated
 1109          * by the address.
 1110          */
 1111         lock = (struct lock_object *)addr;
 1112         tc = TC_LOOKUP(lock);
 1113         LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
 1114                 if (ts->ts_lockobj == lock)
 1115                         goto found;
 1116 
 1117         /*
 1118          * Second, see if there is an active turnstile at the address
 1119          * indicated.
 1120          */
 1121         for (i = 0; i < TC_TABLESIZE; i++)
 1122                 LIST_FOREACH(ts, &turnstile_chains[i].tc_turnstiles, ts_hash) {
 1123                         if (ts == (struct turnstile *)addr)
 1124                                 goto found;
 1125                 }
 1126 
 1127         db_printf("Unable to locate a turnstile via %p\n", (void *)addr);
 1128         return;
 1129 found:
 1130         lock = ts->ts_lockobj;
 1131         db_printf("Lock: %p - (%s) %s\n", lock, LOCK_CLASS(lock)->lc_name,
 1132             lock->lo_name);
 1133         if (ts->ts_owner)
 1134                 print_thread(ts->ts_owner, "Lock Owner: ");
 1135         else
 1136                 db_printf("Lock Owner: none\n");
 1137         print_queue(&ts->ts_blocked[TS_SHARED_QUEUE], "Shared Waiters", "\t");
 1138         print_queue(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE], "Exclusive Waiters",
 1139             "\t");
 1140         print_queue(&ts->ts_pending, "Pending Threads", "\t");
 1141         
 1142 }
 1143 
 1144 /*
 1145  * Show all the threads a particular thread is waiting on based on
 1146  * non-spin locks.
 1147  */
 1148 static void
 1149 print_lockchain(struct thread *td, const char *prefix)
 1150 {
 1151         struct lock_object *lock;
 1152         struct lock_class *class;
 1153         struct turnstile *ts;
 1154         struct thread *owner;
 1155 
 1156         /*
 1157          * Follow the chain.  We keep walking as long as the thread is
 1158          * blocked on a lock that has an owner.
 1159          */
 1160         while (!db_pager_quit) {
 1161                 db_printf("%sthread %d (pid %d, %s) ", prefix, td->td_tid,
 1162                     td->td_proc->p_pid, td->td_name);
 1163                 switch (td->td_state) {
 1164                 case TDS_INACTIVE:
 1165                         db_printf("is inactive\n");
 1166                         return;
 1167                 case TDS_CAN_RUN:
 1168                         db_printf("can run\n");
 1169                         return;
 1170                 case TDS_RUNQ:
 1171                         db_printf("is on a run queue\n");
 1172                         return;
 1173                 case TDS_RUNNING:
 1174                         db_printf("running on CPU %d\n", td->td_oncpu);
 1175                         return;
 1176                 case TDS_INHIBITED:
 1177                         if (TD_ON_LOCK(td)) {
 1178                                 ts = td->td_blocked;
 1179                                 lock = ts->ts_lockobj;
 1180                                 class = LOCK_CLASS(lock);
 1181                                 db_printf("blocked on lock %p (%s) \"%s\"\n",
 1182                                     lock, class->lc_name, lock->lo_name);
 1183                                 if (ts->ts_owner == NULL)
 1184                                         return;
 1185                                 td = ts->ts_owner;
 1186                                 break;
 1187                         } else if (TD_ON_SLEEPQ(td)) {
 1188                                 if (!lockmgr_chain(td, &owner) &&
 1189                                     !sx_chain(td, &owner)) {
 1190                                         db_printf("sleeping on %p \"%s\"\n",
 1191                                             td->td_wchan, td->td_wmesg);
 1192                                         return;
 1193                                 }
 1194                                 if (owner == NULL)
 1195                                         return;
 1196                                 td = owner;
 1197                                 break;
 1198                         }
 1199                         db_printf("inhibited\n");
 1200                         return;
 1201                 default:
 1202                         db_printf("??? (%#x)\n", td->td_state);
 1203                         return;
 1204                 }
 1205         }
 1206 }
 1207 
 1208 DB_SHOW_COMMAND(lockchain, db_show_lockchain)
 1209 {
 1210         struct thread *td;
 1211 
 1212         /* Figure out which thread to start with. */
 1213         if (have_addr)
 1214                 td = db_lookup_thread(addr, true);
 1215         else
 1216                 td = kdb_thread;
 1217 
 1218         print_lockchain(td, "");
 1219 }
 1220 DB_SHOW_ALIAS(sleepchain, db_show_lockchain);
 1221 
 1222 DB_SHOW_ALL_COMMAND(chains, db_show_allchains)
 1223 {
 1224         struct thread *td;
 1225         struct proc *p;
 1226         int i;
 1227 
 1228         i = 1;
 1229         FOREACH_PROC_IN_SYSTEM(p) {
 1230                 FOREACH_THREAD_IN_PROC(p, td) {
 1231                         if ((TD_ON_LOCK(td) && LIST_EMPTY(&td->td_contested))
 1232                             || (TD_IS_INHIBITED(td) && TD_ON_SLEEPQ(td))) {
 1233                                 db_printf("chain %d:\n", i++);
 1234                                 print_lockchain(td, " ");
 1235                         }
 1236                         if (db_pager_quit)
 1237                                 return;
 1238                 }
 1239         }
 1240 }
 1241 DB_SHOW_ALIAS(allchains, db_show_allchains)
 1242 
 1243 static void     print_waiters(struct turnstile *ts, int indent);
 1244         
 1245 static void
 1246 print_waiter(struct thread *td, int indent)
 1247 {
 1248         struct turnstile *ts;
 1249         int i;
 1250 
 1251         if (db_pager_quit)
 1252                 return;
 1253         for (i = 0; i < indent; i++)
 1254                 db_printf(" ");
 1255         print_thread(td, "thread ");
 1256         LIST_FOREACH(ts, &td->td_contested, ts_link)
 1257                 print_waiters(ts, indent + 1);
 1258 }
 1259 
 1260 static void
 1261 print_waiters(struct turnstile *ts, int indent)
 1262 {
 1263         struct lock_object *lock;
 1264         struct lock_class *class;
 1265         struct thread *td;
 1266         int i;
 1267 
 1268         if (db_pager_quit)
 1269                 return;
 1270         lock = ts->ts_lockobj;
 1271         class = LOCK_CLASS(lock);
 1272         for (i = 0; i < indent; i++)
 1273                 db_printf(" ");
 1274         db_printf("lock %p (%s) \"%s\"\n", lock, class->lc_name, lock->lo_name);
 1275         TAILQ_FOREACH(td, &ts->ts_blocked[TS_EXCLUSIVE_QUEUE], td_lockq)
 1276                 print_waiter(td, indent + 1);
 1277         TAILQ_FOREACH(td, &ts->ts_blocked[TS_SHARED_QUEUE], td_lockq)
 1278                 print_waiter(td, indent + 1);
 1279         TAILQ_FOREACH(td, &ts->ts_pending, td_lockq)
 1280                 print_waiter(td, indent + 1);
 1281 }
 1282 
 1283 DB_SHOW_COMMAND(locktree, db_show_locktree)
 1284 {
 1285         struct lock_object *lock;
 1286         struct lock_class *class;
 1287         struct turnstile_chain *tc;
 1288         struct turnstile *ts;
 1289 
 1290         if (!have_addr)
 1291                 return;
 1292         lock = (struct lock_object *)addr;
 1293         tc = TC_LOOKUP(lock);
 1294         LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
 1295                 if (ts->ts_lockobj == lock)
 1296                         break;
 1297         if (ts == NULL) {
 1298                 class = LOCK_CLASS(lock);
 1299                 db_printf("lock %p (%s) \"%s\"\n", lock, class->lc_name,
 1300                     lock->lo_name);
 1301         } else
 1302                 print_waiters(ts, 0);
 1303 }
 1304 #endif

Cache object: 11bc2c4ecada3000a967252539ffa1ed


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]


This page is part of the FreeBSD/Linux Linux Kernel Cross-Reference, and was automatically generated using a modified version of the LXR engine.