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

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    1 /*-
    2  * Copyright (c) 2007 Stephan Uphoff <ups@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  * Machine independent bits of reader/writer lock implementation.
   32  */
   33 
   34 #include <sys/cdefs.h>
   35 __FBSDID("$FreeBSD: releng/10.0/sys/kern/kern_rmlock.c 255745 2013-09-20 23:06:21Z davide $");
   36 
   37 #include "opt_ddb.h"
   38 #include "opt_kdtrace.h"
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 
   43 #include <sys/kernel.h>
   44 #include <sys/kdb.h>
   45 #include <sys/ktr.h>
   46 #include <sys/lock.h>
   47 #include <sys/mutex.h>
   48 #include <sys/proc.h>
   49 #include <sys/rmlock.h>
   50 #include <sys/sched.h>
   51 #include <sys/smp.h>
   52 #include <sys/turnstile.h>
   53 #include <sys/lock_profile.h>
   54 #include <machine/cpu.h>
   55 
   56 #ifdef DDB
   57 #include <ddb/ddb.h>
   58 #endif
   59 
   60 /*
   61  * A cookie to mark destroyed rmlocks.  This is stored in the head of
   62  * rm_activeReaders.
   63  */
   64 #define RM_DESTROYED    ((void *)0xdead)
   65 
   66 #define rm_destroyed(rm)                                                \
   67         (LIST_FIRST(&(rm)->rm_activeReaders) == RM_DESTROYED)
   68 
   69 #define RMPF_ONQUEUE    1
   70 #define RMPF_SIGNAL     2
   71 
   72 #ifndef INVARIANTS
   73 #define _rm_assert(c, what, file, line)
   74 #endif
   75 
   76 static void     assert_rm(const struct lock_object *lock, int what);
   77 #ifdef DDB
   78 static void     db_show_rm(const struct lock_object *lock);
   79 #endif
   80 static void     lock_rm(struct lock_object *lock, uintptr_t how);
   81 #ifdef KDTRACE_HOOKS
   82 static int      owner_rm(const struct lock_object *lock, struct thread **owner);
   83 #endif
   84 static uintptr_t unlock_rm(struct lock_object *lock);
   85 
   86 struct lock_class lock_class_rm = {
   87         .lc_name = "rm",
   88         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
   89         .lc_assert = assert_rm,
   90 #ifdef DDB
   91         .lc_ddb_show = db_show_rm,
   92 #endif
   93         .lc_lock = lock_rm,
   94         .lc_unlock = unlock_rm,
   95 #ifdef KDTRACE_HOOKS
   96         .lc_owner = owner_rm,
   97 #endif
   98 };
   99 
  100 struct lock_class lock_class_rm_sleepable = {
  101         .lc_name = "sleepable rm",
  102         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE,
  103         .lc_assert = assert_rm,
  104 #ifdef DDB
  105         .lc_ddb_show = db_show_rm,
  106 #endif
  107         .lc_lock = lock_rm,
  108         .lc_unlock = unlock_rm,
  109 #ifdef KDTRACE_HOOKS
  110         .lc_owner = owner_rm,
  111 #endif
  112 };
  113 
  114 static void
  115 assert_rm(const struct lock_object *lock, int what)
  116 {
  117 
  118         rm_assert((const struct rmlock *)lock, what);
  119 }
  120 
  121 static void
  122 lock_rm(struct lock_object *lock, uintptr_t how)
  123 {
  124         struct rmlock *rm;
  125         struct rm_priotracker *tracker;
  126 
  127         rm = (struct rmlock *)lock;
  128         if (how == 0)
  129                 rm_wlock(rm);
  130         else {
  131                 tracker = (struct rm_priotracker *)how;
  132                 rm_rlock(rm, tracker);
  133         }
  134 }
  135 
  136 static uintptr_t
  137 unlock_rm(struct lock_object *lock)
  138 {
  139         struct thread *td;
  140         struct pcpu *pc;
  141         struct rmlock *rm;
  142         struct rm_queue *queue;
  143         struct rm_priotracker *tracker;
  144         uintptr_t how;
  145 
  146         rm = (struct rmlock *)lock;
  147         tracker = NULL;
  148         how = 0;
  149         rm_assert(rm, RA_LOCKED | RA_NOTRECURSED);
  150         if (rm_wowned(rm))
  151                 rm_wunlock(rm);
  152         else {
  153                 /*
  154                  * Find the right rm_priotracker structure for curthread.
  155                  * The guarantee about its uniqueness is given by the fact
  156                  * we already asserted the lock wasn't recursively acquired.
  157                  */
  158                 critical_enter();
  159                 td = curthread;
  160                 pc = pcpu_find(curcpu);
  161                 for (queue = pc->pc_rm_queue.rmq_next;
  162                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
  163                         tracker = (struct rm_priotracker *)queue;
  164                                 if ((tracker->rmp_rmlock == rm) &&
  165                                     (tracker->rmp_thread == td)) {
  166                                         how = (uintptr_t)tracker;
  167                                         break;
  168                                 }
  169                 }
  170                 KASSERT(tracker != NULL,
  171                     ("rm_priotracker is non-NULL when lock held in read mode"));
  172                 critical_exit();
  173                 rm_runlock(rm, tracker);
  174         }
  175         return (how);
  176 }
  177 
  178 #ifdef KDTRACE_HOOKS
  179 static int
  180 owner_rm(const struct lock_object *lock, struct thread **owner)
  181 {
  182         const struct rmlock *rm;
  183         struct lock_class *lc;
  184 
  185         rm = (const struct rmlock *)lock;
  186         lc = LOCK_CLASS(&rm->rm_wlock_object);
  187         return (lc->lc_owner(&rm->rm_wlock_object, owner));
  188 }
  189 #endif
  190 
  191 static struct mtx rm_spinlock;
  192 
  193 MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
  194 
  195 /*
  196  * Add or remove tracker from per-cpu list.
  197  *
  198  * The per-cpu list can be traversed at any time in forward direction from an
  199  * interrupt on the *local* cpu.
  200  */
  201 static void inline
  202 rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
  203 {
  204         struct rm_queue *next;
  205 
  206         /* Initialize all tracker pointers */
  207         tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
  208         next = pc->pc_rm_queue.rmq_next;
  209         tracker->rmp_cpuQueue.rmq_next = next;
  210 
  211         /* rmq_prev is not used during froward traversal. */
  212         next->rmq_prev = &tracker->rmp_cpuQueue;
  213 
  214         /* Update pointer to first element. */
  215         pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
  216 }
  217 
  218 /*
  219  * Return a count of the number of trackers the thread 'td' already
  220  * has on this CPU for the lock 'rm'.
  221  */
  222 static int
  223 rm_trackers_present(const struct pcpu *pc, const struct rmlock *rm,
  224     const struct thread *td)
  225 {
  226         struct rm_queue *queue;
  227         struct rm_priotracker *tracker;
  228         int count;
  229 
  230         count = 0;
  231         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
  232             queue = queue->rmq_next) {
  233                 tracker = (struct rm_priotracker *)queue;
  234                 if ((tracker->rmp_rmlock == rm) && (tracker->rmp_thread == td))
  235                         count++;
  236         }
  237         return (count);
  238 }
  239 
  240 static void inline
  241 rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
  242 {
  243         struct rm_queue *next, *prev;
  244 
  245         next = tracker->rmp_cpuQueue.rmq_next;
  246         prev = tracker->rmp_cpuQueue.rmq_prev;
  247 
  248         /* Not used during forward traversal. */
  249         next->rmq_prev = prev;
  250 
  251         /* Remove from list. */
  252         prev->rmq_next = next;
  253 }
  254 
  255 static void
  256 rm_cleanIPI(void *arg)
  257 {
  258         struct pcpu *pc;
  259         struct rmlock *rm = arg;
  260         struct rm_priotracker *tracker;
  261         struct rm_queue *queue;
  262         pc = pcpu_find(curcpu);
  263 
  264         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
  265             queue = queue->rmq_next) {
  266                 tracker = (struct rm_priotracker *)queue;
  267                 if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
  268                         tracker->rmp_flags = RMPF_ONQUEUE;
  269                         mtx_lock_spin(&rm_spinlock);
  270                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
  271                             rmp_qentry);
  272                         mtx_unlock_spin(&rm_spinlock);
  273                 }
  274         }
  275 }
  276 
  277 void
  278 rm_init_flags(struct rmlock *rm, const char *name, int opts)
  279 {
  280         struct lock_class *lc;
  281         int liflags;
  282 
  283         liflags = 0;
  284         if (!(opts & RM_NOWITNESS))
  285                 liflags |= LO_WITNESS;
  286         if (opts & RM_RECURSE)
  287                 liflags |= LO_RECURSABLE;
  288         rm->rm_writecpus = all_cpus;
  289         LIST_INIT(&rm->rm_activeReaders);
  290         if (opts & RM_SLEEPABLE) {
  291                 liflags |= LO_SLEEPABLE;
  292                 lc = &lock_class_rm_sleepable;
  293                 sx_init_flags(&rm->rm_lock_sx, "rmlock_sx", SX_NOWITNESS);
  294         } else {
  295                 lc = &lock_class_rm;
  296                 mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx", MTX_NOWITNESS);
  297         }
  298         lock_init(&rm->lock_object, lc, name, NULL, liflags);
  299 }
  300 
  301 void
  302 rm_init(struct rmlock *rm, const char *name)
  303 {
  304 
  305         rm_init_flags(rm, name, 0);
  306 }
  307 
  308 void
  309 rm_destroy(struct rmlock *rm)
  310 {
  311 
  312         rm_assert(rm, RA_UNLOCKED);
  313         LIST_FIRST(&rm->rm_activeReaders) = RM_DESTROYED;
  314         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  315                 sx_destroy(&rm->rm_lock_sx);
  316         else
  317                 mtx_destroy(&rm->rm_lock_mtx);
  318         lock_destroy(&rm->lock_object);
  319 }
  320 
  321 int
  322 rm_wowned(const struct rmlock *rm)
  323 {
  324 
  325         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  326                 return (sx_xlocked(&rm->rm_lock_sx));
  327         else
  328                 return (mtx_owned(&rm->rm_lock_mtx));
  329 }
  330 
  331 void
  332 rm_sysinit(void *arg)
  333 {
  334         struct rm_args *args = arg;
  335 
  336         rm_init(args->ra_rm, args->ra_desc);
  337 }
  338 
  339 void
  340 rm_sysinit_flags(void *arg)
  341 {
  342         struct rm_args_flags *args = arg;
  343 
  344         rm_init_flags(args->ra_rm, args->ra_desc, args->ra_opts);
  345 }
  346 
  347 static int
  348 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
  349 {
  350         struct pcpu *pc;
  351 
  352         critical_enter();
  353         pc = pcpu_find(curcpu);
  354 
  355         /* Check if we just need to do a proper critical_exit. */
  356         if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
  357                 critical_exit();
  358                 return (1);
  359         }
  360 
  361         /* Remove our tracker from the per-cpu list. */
  362         rm_tracker_remove(pc, tracker);
  363 
  364         /* Check to see if the IPI granted us the lock after all. */
  365         if (tracker->rmp_flags) {
  366                 /* Just add back tracker - we hold the lock. */
  367                 rm_tracker_add(pc, tracker);
  368                 critical_exit();
  369                 return (1);
  370         }
  371 
  372         /*
  373          * We allow readers to aquire a lock even if a writer is blocked if
  374          * the lock is recursive and the reader already holds the lock.
  375          */
  376         if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
  377                 /*
  378                  * Just grant the lock if this thread already has a tracker
  379                  * for this lock on the per-cpu queue.
  380                  */
  381                 if (rm_trackers_present(pc, rm, curthread) != 0) {
  382                         mtx_lock_spin(&rm_spinlock);
  383                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
  384                             rmp_qentry);
  385                         tracker->rmp_flags = RMPF_ONQUEUE;
  386                         mtx_unlock_spin(&rm_spinlock);
  387                         rm_tracker_add(pc, tracker);
  388                         critical_exit();
  389                         return (1);
  390                 }
  391         }
  392 
  393         sched_unpin();
  394         critical_exit();
  395 
  396         if (trylock) {
  397                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
  398                         if (!sx_try_xlock(&rm->rm_lock_sx))
  399                                 return (0);
  400                 } else {
  401                         if (!mtx_trylock(&rm->rm_lock_mtx))
  402                                 return (0);
  403                 }
  404         } else {
  405                 if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  406                         sx_xlock(&rm->rm_lock_sx);
  407                 else
  408                         mtx_lock(&rm->rm_lock_mtx);
  409         }
  410 
  411         critical_enter();
  412         pc = pcpu_find(curcpu);
  413         CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
  414         rm_tracker_add(pc, tracker);
  415         sched_pin();
  416         critical_exit();
  417 
  418         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  419                 sx_xunlock(&rm->rm_lock_sx);
  420         else
  421                 mtx_unlock(&rm->rm_lock_mtx);
  422 
  423         return (1);
  424 }
  425 
  426 int
  427 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
  428 {
  429         struct thread *td = curthread;
  430         struct pcpu *pc;
  431 
  432         if (SCHEDULER_STOPPED())
  433                 return (1);
  434 
  435         tracker->rmp_flags  = 0;
  436         tracker->rmp_thread = td;
  437         tracker->rmp_rmlock = rm;
  438 
  439         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  440                 THREAD_NO_SLEEPING();
  441 
  442         td->td_critnest++;      /* critical_enter(); */
  443 
  444         __compiler_membar();
  445 
  446         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
  447 
  448         rm_tracker_add(pc, tracker);
  449 
  450         sched_pin();
  451 
  452         __compiler_membar();
  453 
  454         td->td_critnest--;
  455 
  456         /*
  457          * Fast path to combine two common conditions into a single
  458          * conditional jump.
  459          */
  460         if (0 == (td->td_owepreempt |
  461             CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)))
  462                 return (1);
  463 
  464         /* We do not have a read token and need to acquire one. */
  465         return _rm_rlock_hard(rm, tracker, trylock);
  466 }
  467 
  468 static void
  469 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
  470 {
  471 
  472         if (td->td_owepreempt) {
  473                 td->td_critnest++;
  474                 critical_exit();
  475         }
  476 
  477         if (!tracker->rmp_flags)
  478                 return;
  479 
  480         mtx_lock_spin(&rm_spinlock);
  481         LIST_REMOVE(tracker, rmp_qentry);
  482 
  483         if (tracker->rmp_flags & RMPF_SIGNAL) {
  484                 struct rmlock *rm;
  485                 struct turnstile *ts;
  486 
  487                 rm = tracker->rmp_rmlock;
  488 
  489                 turnstile_chain_lock(&rm->lock_object);
  490                 mtx_unlock_spin(&rm_spinlock);
  491 
  492                 ts = turnstile_lookup(&rm->lock_object);
  493 
  494                 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
  495                 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
  496                 turnstile_chain_unlock(&rm->lock_object);
  497         } else
  498                 mtx_unlock_spin(&rm_spinlock);
  499 }
  500 
  501 void
  502 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
  503 {
  504         struct pcpu *pc;
  505         struct thread *td = tracker->rmp_thread;
  506 
  507         if (SCHEDULER_STOPPED())
  508                 return;
  509 
  510         td->td_critnest++;      /* critical_enter(); */
  511         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
  512         rm_tracker_remove(pc, tracker);
  513         td->td_critnest--;
  514         sched_unpin();
  515 
  516         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  517                 THREAD_SLEEPING_OK();
  518 
  519         if (0 == (td->td_owepreempt | tracker->rmp_flags))
  520                 return;
  521 
  522         _rm_unlock_hard(td, tracker);
  523 }
  524 
  525 void
  526 _rm_wlock(struct rmlock *rm)
  527 {
  528         struct rm_priotracker *prio;
  529         struct turnstile *ts;
  530         cpuset_t readcpus;
  531 
  532         if (SCHEDULER_STOPPED())
  533                 return;
  534 
  535         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  536                 sx_xlock(&rm->rm_lock_sx);
  537         else
  538                 mtx_lock(&rm->rm_lock_mtx);
  539 
  540         if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
  541                 /* Get all read tokens back */
  542                 readcpus = all_cpus;
  543                 CPU_NAND(&readcpus, &rm->rm_writecpus);
  544                 rm->rm_writecpus = all_cpus;
  545 
  546                 /*
  547                  * Assumes rm->rm_writecpus update is visible on other CPUs
  548                  * before rm_cleanIPI is called.
  549                  */
  550 #ifdef SMP
  551                 smp_rendezvous_cpus(readcpus,
  552                     smp_no_rendevous_barrier,
  553                     rm_cleanIPI,
  554                     smp_no_rendevous_barrier,
  555                     rm);
  556 
  557 #else
  558                 rm_cleanIPI(rm);
  559 #endif
  560 
  561                 mtx_lock_spin(&rm_spinlock);
  562                 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
  563                         ts = turnstile_trywait(&rm->lock_object);
  564                         prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
  565                         mtx_unlock_spin(&rm_spinlock);
  566                         turnstile_wait(ts, prio->rmp_thread,
  567                             TS_EXCLUSIVE_QUEUE);
  568                         mtx_lock_spin(&rm_spinlock);
  569                 }
  570                 mtx_unlock_spin(&rm_spinlock);
  571         }
  572 }
  573 
  574 void
  575 _rm_wunlock(struct rmlock *rm)
  576 {
  577 
  578         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  579                 sx_xunlock(&rm->rm_lock_sx);
  580         else
  581                 mtx_unlock(&rm->rm_lock_mtx);
  582 }
  583 
  584 #ifdef LOCK_DEBUG
  585 
  586 void
  587 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
  588 {
  589 
  590         if (SCHEDULER_STOPPED())
  591                 return;
  592 
  593         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  594             ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
  595             curthread, rm->lock_object.lo_name, file, line));
  596         KASSERT(!rm_destroyed(rm),
  597             ("rm_wlock() of destroyed rmlock @ %s:%d", file, line));
  598         _rm_assert(rm, RA_UNLOCKED, file, line);
  599 
  600         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
  601             file, line, NULL);
  602 
  603         _rm_wlock(rm);
  604 
  605         LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
  606 
  607         WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
  608 
  609         curthread->td_locks++;
  610 
  611 }
  612 
  613 void
  614 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
  615 {
  616 
  617         if (SCHEDULER_STOPPED())
  618                 return;
  619 
  620         KASSERT(!rm_destroyed(rm),
  621             ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
  622         _rm_assert(rm, RA_WLOCKED, file, line);
  623         WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
  624         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
  625         _rm_wunlock(rm);
  626         curthread->td_locks--;
  627 }
  628 
  629 int
  630 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
  631     int trylock, const char *file, int line)
  632 {
  633 
  634         if (SCHEDULER_STOPPED())
  635                 return (1);
  636 
  637 #ifdef INVARIANTS
  638         if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
  639                 critical_enter();
  640                 KASSERT(rm_trackers_present(pcpu_find(curcpu), rm,
  641                     curthread) == 0,
  642                     ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
  643                     rm->lock_object.lo_name, file, line));
  644                 critical_exit();
  645         }
  646 #endif
  647         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  648             ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
  649             curthread, rm->lock_object.lo_name, file, line));
  650         KASSERT(!rm_destroyed(rm),
  651             ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
  652         if (!trylock) {
  653                 KASSERT(!rm_wowned(rm),
  654                     ("rm_rlock: wlock already held for %s @ %s:%d",
  655                     rm->lock_object.lo_name, file, line));
  656                 WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER, file, line,
  657                     NULL);
  658         }
  659 
  660         if (_rm_rlock(rm, tracker, trylock)) {
  661                 if (trylock)
  662                         LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
  663                             line);
  664                 else
  665                         LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
  666                             line);
  667                 WITNESS_LOCK(&rm->lock_object, 0, file, line);
  668 
  669                 curthread->td_locks++;
  670 
  671                 return (1);
  672         } else if (trylock)
  673                 LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
  674 
  675         return (0);
  676 }
  677 
  678 void
  679 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
  680     const char *file, int line)
  681 {
  682 
  683         if (SCHEDULER_STOPPED())
  684                 return;
  685 
  686         KASSERT(!rm_destroyed(rm),
  687             ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
  688         _rm_assert(rm, RA_RLOCKED, file, line);
  689         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
  690         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
  691         _rm_runlock(rm, tracker);
  692         curthread->td_locks--;
  693 }
  694 
  695 #else
  696 
  697 /*
  698  * Just strip out file and line arguments if no lock debugging is enabled in
  699  * the kernel - we are called from a kernel module.
  700  */
  701 void
  702 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
  703 {
  704 
  705         _rm_wlock(rm);
  706 }
  707 
  708 void
  709 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
  710 {
  711 
  712         _rm_wunlock(rm);
  713 }
  714 
  715 int
  716 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
  717     int trylock, const char *file, int line)
  718 {
  719 
  720         return _rm_rlock(rm, tracker, trylock);
  721 }
  722 
  723 void
  724 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
  725     const char *file, int line)
  726 {
  727 
  728         _rm_runlock(rm, tracker);
  729 }
  730 
  731 #endif
  732 
  733 #ifdef INVARIANT_SUPPORT
  734 #ifndef INVARIANTS
  735 #undef _rm_assert
  736 #endif
  737 
  738 /*
  739  * Note that this does not need to use witness_assert() for read lock
  740  * assertions since an exact count of read locks held by this thread
  741  * is computable.
  742  */
  743 void
  744 _rm_assert(const struct rmlock *rm, int what, const char *file, int line)
  745 {
  746         int count;
  747 
  748         if (panicstr != NULL)
  749                 return;
  750         switch (what) {
  751         case RA_LOCKED:
  752         case RA_LOCKED | RA_RECURSED:
  753         case RA_LOCKED | RA_NOTRECURSED:
  754         case RA_RLOCKED:
  755         case RA_RLOCKED | RA_RECURSED:
  756         case RA_RLOCKED | RA_NOTRECURSED:
  757                 /*
  758                  * Handle the write-locked case.  Unlike other
  759                  * primitives, writers can never recurse.
  760                  */
  761                 if (rm_wowned(rm)) {
  762                         if (what & RA_RLOCKED)
  763                                 panic("Lock %s exclusively locked @ %s:%d\n",
  764                                     rm->lock_object.lo_name, file, line);
  765                         if (what & RA_RECURSED)
  766                                 panic("Lock %s not recursed @ %s:%d\n",
  767                                     rm->lock_object.lo_name, file, line);
  768                         break;
  769                 }
  770 
  771                 critical_enter();
  772                 count = rm_trackers_present(pcpu_find(curcpu), rm, curthread);
  773                 critical_exit();
  774 
  775                 if (count == 0)
  776                         panic("Lock %s not %slocked @ %s:%d\n",
  777                             rm->lock_object.lo_name, (what & RA_RLOCKED) ?
  778                             "read " : "", file, line);
  779                 if (count > 1) {
  780                         if (what & RA_NOTRECURSED)
  781                                 panic("Lock %s recursed @ %s:%d\n",
  782                                     rm->lock_object.lo_name, file, line);
  783                 } else if (what & RA_RECURSED)
  784                         panic("Lock %s not recursed @ %s:%d\n",
  785                             rm->lock_object.lo_name, file, line);
  786                 break;
  787         case RA_WLOCKED:
  788                 if (!rm_wowned(rm))
  789                         panic("Lock %s not exclusively locked @ %s:%d\n",
  790                             rm->lock_object.lo_name, file, line);
  791                 break;
  792         case RA_UNLOCKED:
  793                 if (rm_wowned(rm))
  794                         panic("Lock %s exclusively locked @ %s:%d\n",
  795                             rm->lock_object.lo_name, file, line);
  796 
  797                 critical_enter();
  798                 count = rm_trackers_present(pcpu_find(curcpu), rm, curthread);
  799                 critical_exit();
  800 
  801                 if (count != 0)
  802                         panic("Lock %s read locked @ %s:%d\n",
  803                             rm->lock_object.lo_name, file, line);
  804                 break;
  805         default:
  806                 panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
  807                     line);
  808         }
  809 }
  810 #endif /* INVARIANT_SUPPORT */
  811 
  812 #ifdef DDB
  813 static void
  814 print_tracker(struct rm_priotracker *tr)
  815 {
  816         struct thread *td;
  817 
  818         td = tr->rmp_thread;
  819         db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
  820             td->td_proc->p_pid, td->td_name);
  821         if (tr->rmp_flags & RMPF_ONQUEUE) {
  822                 db_printf("ONQUEUE");
  823                 if (tr->rmp_flags & RMPF_SIGNAL)
  824                         db_printf(",SIGNAL");
  825         } else
  826                 db_printf("");
  827         db_printf("}\n");
  828 }
  829 
  830 static void
  831 db_show_rm(const struct lock_object *lock)
  832 {
  833         struct rm_priotracker *tr;
  834         struct rm_queue *queue;
  835         const struct rmlock *rm;
  836         struct lock_class *lc;
  837         struct pcpu *pc;
  838 
  839         rm = (const struct rmlock *)lock;
  840         db_printf(" writecpus: ");
  841         ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
  842         db_printf("\n");
  843         db_printf(" per-CPU readers:\n");
  844         STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
  845                 for (queue = pc->pc_rm_queue.rmq_next;
  846                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
  847                         tr = (struct rm_priotracker *)queue;
  848                         if (tr->rmp_rmlock == rm)
  849                                 print_tracker(tr);
  850                 }
  851         db_printf(" active readers:\n");
  852         LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
  853                 print_tracker(tr);
  854         lc = LOCK_CLASS(&rm->rm_wlock_object);
  855         db_printf("Backing write-lock (%s):\n", lc->lc_name);
  856         lc->lc_ddb_show(&rm->rm_wlock_object);
  857 }
  858 #endif

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