kern_rmlock.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 2007 Stephan Uphoff <ups@FreeBSD.org>
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  * 3. Neither the name of the author nor the names of any co-contributors
   16  *    may be used to endorse or promote products derived from this software
   17  *    without specific prior written permission.
   18  *
   19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  */
   31 
   32 /*
   33  * Machine independent bits of reader/writer lock implementation.
   34  */
   35 
   36 #include <sys/cdefs.h>
   37 __FBSDID("$FreeBSD$");
   38 
   39 #include "opt_ddb.h"
   40 
   41 #include <sys/param.h>
   42 #include <sys/systm.h>
   43 
   44 #include <sys/kernel.h>
   45 #include <sys/kdb.h>
   46 #include <sys/ktr.h>
   47 #include <sys/lock.h>
   48 #include <sys/mutex.h>
   49 #include <sys/proc.h>
   50 #include <sys/rmlock.h>
   51 #include <sys/sched.h>
   52 #include <sys/smp.h>
   53 #include <sys/turnstile.h>
   54 #include <sys/lock_profile.h>
   55 #include <machine/cpu.h>
   56 #include <vm/uma.h>
   57 
   58 #ifdef DDB
   59 #include <ddb/ddb.h>
   60 #endif
   61 
   62 /*
   63  * A cookie to mark destroyed rmlocks.  This is stored in the head of
   64  * rm_activeReaders.
   65  */
   66 #define RM_DESTROYED    ((void *)0xdead)
   67 
   68 #define rm_destroyed(rm)                                                \
   69         (LIST_FIRST(&(rm)->rm_activeReaders) == RM_DESTROYED)
   70 
   71 #define RMPF_ONQUEUE    1
   72 #define RMPF_SIGNAL     2
   73 
   74 #ifndef INVARIANTS
   75 #define _rm_assert(c, what, file, line)
   76 #endif
   77 
   78 static void     assert_rm(const struct lock_object *lock, int what);
   79 #ifdef DDB
   80 static void     db_show_rm(const struct lock_object *lock);
   81 #endif
   82 static void     lock_rm(struct lock_object *lock, uintptr_t how);
   83 #ifdef KDTRACE_HOOKS
   84 static int      owner_rm(const struct lock_object *lock, struct thread **owner);
   85 #endif
   86 static uintptr_t unlock_rm(struct lock_object *lock);
   87 
   88 struct lock_class lock_class_rm = {
   89         .lc_name = "rm",
   90         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
   91         .lc_assert = assert_rm,
   92 #ifdef DDB
   93         .lc_ddb_show = db_show_rm,
   94 #endif
   95         .lc_lock = lock_rm,
   96         .lc_unlock = unlock_rm,
   97 #ifdef KDTRACE_HOOKS
   98         .lc_owner = owner_rm,
   99 #endif
  100 };
  101 
  102 struct lock_class lock_class_rm_sleepable = {
  103         .lc_name = "sleepable rm",
  104         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE,
  105         .lc_assert = assert_rm,
  106 #ifdef DDB
  107         .lc_ddb_show = db_show_rm,
  108 #endif
  109         .lc_lock = lock_rm,
  110         .lc_unlock = unlock_rm,
  111 #ifdef KDTRACE_HOOKS
  112         .lc_owner = owner_rm,
  113 #endif
  114 };
  115 
  116 static void
  117 assert_rm(const struct lock_object *lock, int what)
  118 {
  119 
  120         rm_assert((const struct rmlock *)lock, what);
  121 }
  122 
  123 static void
  124 lock_rm(struct lock_object *lock, uintptr_t how)
  125 {
  126         struct rmlock *rm;
  127         struct rm_priotracker *tracker;
  128 
  129         rm = (struct rmlock *)lock;
  130         if (how == 0)
  131                 rm_wlock(rm);
  132         else {
  133                 tracker = (struct rm_priotracker *)how;
  134                 rm_rlock(rm, tracker);
  135         }
  136 }
  137 
  138 static uintptr_t
  139 unlock_rm(struct lock_object *lock)
  140 {
  141         struct thread *td;
  142         struct pcpu *pc;
  143         struct rmlock *rm;
  144         struct rm_queue *queue;
  145         struct rm_priotracker *tracker;
  146         uintptr_t how;
  147 
  148         rm = (struct rmlock *)lock;
  149         tracker = NULL;
  150         how = 0;
  151         rm_assert(rm, RA_LOCKED | RA_NOTRECURSED);
  152         if (rm_wowned(rm))
  153                 rm_wunlock(rm);
  154         else {
  155                 /*
  156                  * Find the right rm_priotracker structure for curthread.
  157                  * The guarantee about its uniqueness is given by the fact
  158                  * we already asserted the lock wasn't recursively acquired.
  159                  */
  160                 critical_enter();
  161                 td = curthread;
  162                 pc = get_pcpu();
  163                 for (queue = pc->pc_rm_queue.rmq_next;
  164                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
  165                         tracker = (struct rm_priotracker *)queue;
  166                                 if ((tracker->rmp_rmlock == rm) &&
  167                                     (tracker->rmp_thread == td)) {
  168                                         how = (uintptr_t)tracker;
  169                                         break;
  170                                 }
  171                 }
  172                 KASSERT(tracker != NULL,
  173                     ("rm_priotracker is non-NULL when lock held in read mode"));
  174                 critical_exit();
  175                 rm_runlock(rm, tracker);
  176         }
  177         return (how);
  178 }
  179 
  180 #ifdef KDTRACE_HOOKS
  181 static int
  182 owner_rm(const struct lock_object *lock, struct thread **owner)
  183 {
  184         const struct rmlock *rm;
  185         struct lock_class *lc;
  186 
  187         rm = (const struct rmlock *)lock;
  188         lc = LOCK_CLASS(&rm->rm_wlock_object);
  189         return (lc->lc_owner(&rm->rm_wlock_object, owner));
  190 }
  191 #endif
  192 
  193 static struct mtx rm_spinlock;
  194 
  195 MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
  196 
  197 /*
  198  * Add or remove tracker from per-cpu list.
  199  *
  200  * The per-cpu list can be traversed at any time in forward direction from an
  201  * interrupt on the *local* cpu.
  202  */
  203 static void inline
  204 rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
  205 {
  206         struct rm_queue *next;
  207 
  208         /* Initialize all tracker pointers */
  209         tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
  210         next = pc->pc_rm_queue.rmq_next;
  211         tracker->rmp_cpuQueue.rmq_next = next;
  212 
  213         /* rmq_prev is not used during froward traversal. */
  214         next->rmq_prev = &tracker->rmp_cpuQueue;
  215 
  216         /* Update pointer to first element. */
  217         pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
  218 }
  219 
  220 /*
  221  * Return a count of the number of trackers the thread 'td' already
  222  * has on this CPU for the lock 'rm'.
  223  */
  224 static int
  225 rm_trackers_present(const struct pcpu *pc, const struct rmlock *rm,
  226     const struct thread *td)
  227 {
  228         struct rm_queue *queue;
  229         struct rm_priotracker *tracker;
  230         int count;
  231 
  232         count = 0;
  233         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
  234             queue = queue->rmq_next) {
  235                 tracker = (struct rm_priotracker *)queue;
  236                 if ((tracker->rmp_rmlock == rm) && (tracker->rmp_thread == td))
  237                         count++;
  238         }
  239         return (count);
  240 }
  241 
  242 static void inline
  243 rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
  244 {
  245         struct rm_queue *next, *prev;
  246 
  247         next = tracker->rmp_cpuQueue.rmq_next;
  248         prev = tracker->rmp_cpuQueue.rmq_prev;
  249 
  250         /* Not used during forward traversal. */
  251         next->rmq_prev = prev;
  252 
  253         /* Remove from list. */
  254         prev->rmq_next = next;
  255 }
  256 
  257 static void
  258 rm_cleanIPI(void *arg)
  259 {
  260         struct pcpu *pc;
  261         struct rmlock *rm = arg;
  262         struct rm_priotracker *tracker;
  263         struct rm_queue *queue;
  264         pc = get_pcpu();
  265 
  266         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
  267             queue = queue->rmq_next) {
  268                 tracker = (struct rm_priotracker *)queue;
  269                 if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
  270                         tracker->rmp_flags = RMPF_ONQUEUE;
  271                         mtx_lock_spin(&rm_spinlock);
  272                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
  273                             rmp_qentry);
  274                         mtx_unlock_spin(&rm_spinlock);
  275                 }
  276         }
  277 }
  278 
  279 void
  280 rm_init_flags(struct rmlock *rm, const char *name, int opts)
  281 {
  282         struct lock_class *lc;
  283         int liflags, xflags;
  284 
  285         liflags = 0;
  286         if (!(opts & RM_NOWITNESS))
  287                 liflags |= LO_WITNESS;
  288         if (opts & RM_RECURSE)
  289                 liflags |= LO_RECURSABLE;
  290         if (opts & RM_NEW)
  291                 liflags |= LO_NEW;
  292         if (opts & RM_DUPOK)
  293                 liflags |= LO_DUPOK;
  294         rm->rm_writecpus = all_cpus;
  295         LIST_INIT(&rm->rm_activeReaders);
  296         if (opts & RM_SLEEPABLE) {
  297                 liflags |= LO_SLEEPABLE;
  298                 lc = &lock_class_rm_sleepable;
  299                 xflags = (opts & RM_NEW ? SX_NEW : 0);
  300                 sx_init_flags(&rm->rm_lock_sx, "rmlock_sx",
  301                     xflags | SX_NOWITNESS);
  302         } else {
  303                 lc = &lock_class_rm;
  304                 xflags = (opts & RM_NEW ? MTX_NEW : 0);
  305                 mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx",
  306                     xflags | MTX_NOWITNESS);
  307         }
  308         lock_init(&rm->lock_object, lc, name, NULL, liflags);
  309 }
  310 
  311 void
  312 rm_init(struct rmlock *rm, const char *name)
  313 {
  314 
  315         rm_init_flags(rm, name, 0);
  316 }
  317 
  318 void
  319 rm_destroy(struct rmlock *rm)
  320 {
  321 
  322         rm_assert(rm, RA_UNLOCKED);
  323         LIST_FIRST(&rm->rm_activeReaders) = RM_DESTROYED;
  324         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  325                 sx_destroy(&rm->rm_lock_sx);
  326         else
  327                 mtx_destroy(&rm->rm_lock_mtx);
  328         lock_destroy(&rm->lock_object);
  329 }
  330 
  331 int
  332 rm_wowned(const struct rmlock *rm)
  333 {
  334 
  335         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  336                 return (sx_xlocked(&rm->rm_lock_sx));
  337         else
  338                 return (mtx_owned(&rm->rm_lock_mtx));
  339 }
  340 
  341 void
  342 rm_sysinit(void *arg)
  343 {
  344         struct rm_args *args;
  345 
  346         args = arg;
  347         rm_init_flags(args->ra_rm, args->ra_desc, args->ra_flags);
  348 }
  349 
  350 static __noinline int
  351 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
  352 {
  353         struct pcpu *pc;
  354 
  355         critical_enter();
  356         pc = get_pcpu();
  357 
  358         /* Check if we just need to do a proper critical_exit. */
  359         if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
  360                 critical_exit();
  361                 return (1);
  362         }
  363 
  364         /* Remove our tracker from the per-cpu list. */
  365         rm_tracker_remove(pc, tracker);
  366 
  367         /*
  368          * Check to see if the IPI granted us the lock after all.  The load of
  369          * rmp_flags must happen after the tracker is removed from the list.
  370          */
  371         atomic_interrupt_fence();
  372         if (tracker->rmp_flags) {
  373                 /* Just add back tracker - we hold the lock. */
  374                 rm_tracker_add(pc, tracker);
  375                 critical_exit();
  376                 return (1);
  377         }
  378 
  379         /*
  380          * We allow readers to acquire a lock even if a writer is blocked if
  381          * the lock is recursive and the reader already holds the lock.
  382          */
  383         if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
  384                 /*
  385                  * Just grant the lock if this thread already has a tracker
  386                  * for this lock on the per-cpu queue.
  387                  */
  388                 if (rm_trackers_present(pc, rm, curthread) != 0) {
  389                         mtx_lock_spin(&rm_spinlock);
  390                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
  391                             rmp_qentry);
  392                         tracker->rmp_flags = RMPF_ONQUEUE;
  393                         mtx_unlock_spin(&rm_spinlock);
  394                         rm_tracker_add(pc, tracker);
  395                         critical_exit();
  396                         return (1);
  397                 }
  398         }
  399 
  400         sched_unpin();
  401         critical_exit();
  402 
  403         if (trylock) {
  404                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
  405                         if (!sx_try_xlock(&rm->rm_lock_sx))
  406                                 return (0);
  407                 } else {
  408                         if (!mtx_trylock(&rm->rm_lock_mtx))
  409                                 return (0);
  410                 }
  411         } else {
  412                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
  413                         THREAD_SLEEPING_OK();
  414                         sx_xlock(&rm->rm_lock_sx);
  415                         THREAD_NO_SLEEPING();
  416                 } else
  417                         mtx_lock(&rm->rm_lock_mtx);
  418         }
  419 
  420         critical_enter();
  421         pc = get_pcpu();
  422         CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
  423         rm_tracker_add(pc, tracker);
  424         sched_pin();
  425         critical_exit();
  426 
  427         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  428                 sx_xunlock(&rm->rm_lock_sx);
  429         else
  430                 mtx_unlock(&rm->rm_lock_mtx);
  431 
  432         return (1);
  433 }
  434 
  435 int
  436 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
  437 {
  438         struct thread *td = curthread;
  439         struct pcpu *pc;
  440 
  441         if (SCHEDULER_STOPPED())
  442                 return (1);
  443 
  444         tracker->rmp_flags  = 0;
  445         tracker->rmp_thread = td;
  446         tracker->rmp_rmlock = rm;
  447 
  448         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  449                 THREAD_NO_SLEEPING();
  450 
  451         td->td_critnest++;      /* critical_enter(); */
  452         atomic_interrupt_fence();
  453 
  454         pc = cpuid_to_pcpu[td->td_oncpu];
  455         rm_tracker_add(pc, tracker);
  456         sched_pin();
  457 
  458         atomic_interrupt_fence();
  459         td->td_critnest--;
  460 
  461         /*
  462          * Fast path to combine two common conditions into a single
  463          * conditional jump.
  464          */
  465         if (__predict_true(0 == (td->td_owepreempt |
  466             CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus))))
  467                 return (1);
  468 
  469         /* We do not have a read token and need to acquire one. */
  470         return _rm_rlock_hard(rm, tracker, trylock);
  471 }
  472 
  473 static __noinline void
  474 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
  475 {
  476 
  477         if (td->td_owepreempt) {
  478                 td->td_critnest++;
  479                 critical_exit();
  480         }
  481 
  482         if (!tracker->rmp_flags)
  483                 return;
  484 
  485         mtx_lock_spin(&rm_spinlock);
  486         LIST_REMOVE(tracker, rmp_qentry);
  487 
  488         if (tracker->rmp_flags & RMPF_SIGNAL) {
  489                 struct rmlock *rm;
  490                 struct turnstile *ts;
  491 
  492                 rm = tracker->rmp_rmlock;
  493 
  494                 turnstile_chain_lock(&rm->lock_object);
  495                 mtx_unlock_spin(&rm_spinlock);
  496 
  497                 ts = turnstile_lookup(&rm->lock_object);
  498 
  499                 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
  500                 turnstile_unpend(ts);
  501                 turnstile_chain_unlock(&rm->lock_object);
  502         } else
  503                 mtx_unlock_spin(&rm_spinlock);
  504 }
  505 
  506 void
  507 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
  508 {
  509         struct pcpu *pc;
  510         struct thread *td = tracker->rmp_thread;
  511 
  512         if (SCHEDULER_STOPPED())
  513                 return;
  514 
  515         td->td_critnest++;      /* critical_enter(); */
  516         atomic_interrupt_fence();
  517 
  518         pc = cpuid_to_pcpu[td->td_oncpu];
  519         rm_tracker_remove(pc, tracker);
  520 
  521         atomic_interrupt_fence();
  522         td->td_critnest--;
  523         sched_unpin();
  524 
  525         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  526                 THREAD_SLEEPING_OK();
  527 
  528         if (__predict_true(0 == (td->td_owepreempt | tracker->rmp_flags)))
  529                 return;
  530 
  531         _rm_unlock_hard(td, tracker);
  532 }
  533 
  534 void
  535 _rm_wlock(struct rmlock *rm)
  536 {
  537         struct rm_priotracker *prio;
  538         struct turnstile *ts;
  539         cpuset_t readcpus;
  540 
  541         if (SCHEDULER_STOPPED())
  542                 return;
  543 
  544         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  545                 sx_xlock(&rm->rm_lock_sx);
  546         else
  547                 mtx_lock(&rm->rm_lock_mtx);
  548 
  549         if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
  550                 /* Get all read tokens back */
  551                 readcpus = all_cpus;
  552                 CPU_ANDNOT(&readcpus, &readcpus, &rm->rm_writecpus);
  553                 rm->rm_writecpus = all_cpus;
  554 
  555                 /*
  556                  * Assumes rm->rm_writecpus update is visible on other CPUs
  557                  * before rm_cleanIPI is called.
  558                  */
  559 #ifdef SMP
  560                 smp_rendezvous_cpus(readcpus,
  561                     smp_no_rendezvous_barrier,
  562                     rm_cleanIPI,
  563                     smp_no_rendezvous_barrier,
  564                     rm);
  565 
  566 #else
  567                 rm_cleanIPI(rm);
  568 #endif
  569 
  570                 mtx_lock_spin(&rm_spinlock);
  571                 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
  572                         ts = turnstile_trywait(&rm->lock_object);
  573                         prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
  574                         mtx_unlock_spin(&rm_spinlock);
  575                         turnstile_wait(ts, prio->rmp_thread,
  576                             TS_EXCLUSIVE_QUEUE);
  577                         mtx_lock_spin(&rm_spinlock);
  578                 }
  579                 mtx_unlock_spin(&rm_spinlock);
  580         }
  581 }
  582 
  583 void
  584 _rm_wunlock(struct rmlock *rm)
  585 {
  586 
  587         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
  588                 sx_xunlock(&rm->rm_lock_sx);
  589         else
  590                 mtx_unlock(&rm->rm_lock_mtx);
  591 }
  592 
  593 #if LOCK_DEBUG > 0
  594 
  595 void
  596 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
  597 {
  598 
  599         if (SCHEDULER_STOPPED())
  600                 return;
  601 
  602         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  603             ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
  604             curthread, rm->lock_object.lo_name, file, line));
  605         KASSERT(!rm_destroyed(rm),
  606             ("rm_wlock() of destroyed rmlock @ %s:%d", file, line));
  607         _rm_assert(rm, RA_UNLOCKED, file, line);
  608 
  609         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
  610             file, line, NULL);
  611 
  612         _rm_wlock(rm);
  613 
  614         LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
  615         WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
  616         TD_LOCKS_INC(curthread);
  617 }
  618 
  619 void
  620 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
  621 {
  622 
  623         if (SCHEDULER_STOPPED())
  624                 return;
  625 
  626         KASSERT(!rm_destroyed(rm),
  627             ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
  628         _rm_assert(rm, RA_WLOCKED, file, line);
  629         WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
  630         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
  631         _rm_wunlock(rm);
  632         TD_LOCKS_DEC(curthread);
  633 }
  634 
  635 int
  636 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
  637     int trylock, const char *file, int line)
  638 {
  639 
  640         if (SCHEDULER_STOPPED())
  641                 return (1);
  642 
  643 #ifdef INVARIANTS
  644         if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
  645                 critical_enter();
  646                 KASSERT(rm_trackers_present(get_pcpu(), rm,
  647                     curthread) == 0,
  648                     ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
  649                     rm->lock_object.lo_name, file, line));
  650                 critical_exit();
  651         }
  652 #endif
  653         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  654             ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
  655             curthread, rm->lock_object.lo_name, file, line));
  656         KASSERT(!rm_destroyed(rm),
  657             ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
  658         if (!trylock) {
  659                 KASSERT(!rm_wowned(rm),
  660                     ("rm_rlock: wlock already held for %s @ %s:%d",
  661                     rm->lock_object.lo_name, file, line));
  662                 WITNESS_CHECKORDER(&rm->lock_object,
  663                     LOP_NEWORDER | LOP_NOSLEEP, file, line, NULL);
  664         }
  665 
  666         if (_rm_rlock(rm, tracker, trylock)) {
  667                 if (trylock)
  668                         LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
  669                             line);
  670                 else
  671                         LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
  672                             line);
  673                 WITNESS_LOCK(&rm->lock_object, LOP_NOSLEEP, file, line);
  674                 TD_LOCKS_INC(curthread);
  675                 return (1);
  676         } else if (trylock)
  677                 LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
  678 
  679         return (0);
  680 }
  681 
  682 void
  683 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
  684     const char *file, int line)
  685 {
  686 
  687         if (SCHEDULER_STOPPED())
  688                 return;
  689 
  690         KASSERT(!rm_destroyed(rm),
  691             ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
  692         _rm_assert(rm, RA_RLOCKED, file, line);
  693         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
  694         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
  695         _rm_runlock(rm, tracker);
  696         TD_LOCKS_DEC(curthread);
  697 }
  698 
  699 #else
  700 
  701 /*
  702  * Just strip out file and line arguments if no lock debugging is enabled in
  703  * the kernel - we are called from a kernel module.
  704  */
  705 void
  706 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
  707 {
  708 
  709         _rm_wlock(rm);
  710 }
  711 
  712 void
  713 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
  714 {
  715 
  716         _rm_wunlock(rm);
  717 }
  718 
  719 int
  720 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
  721     int trylock, const char *file, int line)
  722 {
  723 
  724         return _rm_rlock(rm, tracker, trylock);
  725 }
  726 
  727 void
  728 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
  729     const char *file, int line)
  730 {
  731 
  732         _rm_runlock(rm, tracker);
  733 }
  734 
  735 #endif
  736 
  737 #ifdef INVARIANT_SUPPORT
  738 #ifndef INVARIANTS
  739 #undef _rm_assert
  740 #endif
  741 
  742 /*
  743  * Note that this does not need to use witness_assert() for read lock
  744  * assertions since an exact count of read locks held by this thread
  745  * is computable.
  746  */
  747 void
  748 _rm_assert(const struct rmlock *rm, int what, const char *file, int line)
  749 {
  750         int count;
  751 
  752         if (SCHEDULER_STOPPED())
  753                 return;
  754         switch (what) {
  755         case RA_LOCKED:
  756         case RA_LOCKED | RA_RECURSED:
  757         case RA_LOCKED | RA_NOTRECURSED:
  758         case RA_RLOCKED:
  759         case RA_RLOCKED | RA_RECURSED:
  760         case RA_RLOCKED | RA_NOTRECURSED:
  761                 /*
  762                  * Handle the write-locked case.  Unlike other
  763                  * primitives, writers can never recurse.
  764                  */
  765                 if (rm_wowned(rm)) {
  766                         if (what & RA_RLOCKED)
  767                                 panic("Lock %s exclusively locked @ %s:%d\n",
  768                                     rm->lock_object.lo_name, file, line);
  769                         if (what & RA_RECURSED)
  770                                 panic("Lock %s not recursed @ %s:%d\n",
  771                                     rm->lock_object.lo_name, file, line);
  772                         break;
  773                 }
  774 
  775                 critical_enter();
  776                 count = rm_trackers_present(get_pcpu(), rm, curthread);
  777                 critical_exit();
  778 
  779                 if (count == 0)
  780                         panic("Lock %s not %slocked @ %s:%d\n",
  781                             rm->lock_object.lo_name, (what & RA_RLOCKED) ?
  782                             "read " : "", file, line);
  783                 if (count > 1) {
  784                         if (what & RA_NOTRECURSED)
  785                                 panic("Lock %s recursed @ %s:%d\n",
  786                                     rm->lock_object.lo_name, file, line);
  787                 } else if (what & RA_RECURSED)
  788                         panic("Lock %s not recursed @ %s:%d\n",
  789                             rm->lock_object.lo_name, file, line);
  790                 break;
  791         case RA_WLOCKED:
  792                 if (!rm_wowned(rm))
  793                         panic("Lock %s not exclusively locked @ %s:%d\n",
  794                             rm->lock_object.lo_name, file, line);
  795                 break;
  796         case RA_UNLOCKED:
  797                 if (rm_wowned(rm))
  798                         panic("Lock %s exclusively locked @ %s:%d\n",
  799                             rm->lock_object.lo_name, file, line);
  800 
  801                 critical_enter();
  802                 count = rm_trackers_present(get_pcpu(), rm, curthread);
  803                 critical_exit();
  804 
  805                 if (count != 0)
  806                         panic("Lock %s read locked @ %s:%d\n",
  807                             rm->lock_object.lo_name, file, line);
  808                 break;
  809         default:
  810                 panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
  811                     line);
  812         }
  813 }
  814 #endif /* INVARIANT_SUPPORT */
  815 
  816 #ifdef DDB
  817 static void
  818 print_tracker(struct rm_priotracker *tr)
  819 {
  820         struct thread *td;
  821 
  822         td = tr->rmp_thread;
  823         db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
  824             td->td_proc->p_pid, td->td_name);
  825         if (tr->rmp_flags & RMPF_ONQUEUE) {
  826                 db_printf("ONQUEUE");
  827                 if (tr->rmp_flags & RMPF_SIGNAL)
  828                         db_printf(",SIGNAL");
  829         } else
  830                 db_printf("");
  831         db_printf("}\n");
  832 }
  833 
  834 static void
  835 db_show_rm(const struct lock_object *lock)
  836 {
  837         struct rm_priotracker *tr;
  838         struct rm_queue *queue;
  839         const struct rmlock *rm;
  840         struct lock_class *lc;
  841         struct pcpu *pc;
  842 
  843         rm = (const struct rmlock *)lock;
  844         db_printf(" writecpus: ");
  845         ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
  846         db_printf("\n");
  847         db_printf(" per-CPU readers:\n");
  848         STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
  849                 for (queue = pc->pc_rm_queue.rmq_next;
  850                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
  851                         tr = (struct rm_priotracker *)queue;
  852                         if (tr->rmp_rmlock == rm)
  853                                 print_tracker(tr);
  854                 }
  855         db_printf(" active readers:\n");
  856         LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
  857                 print_tracker(tr);
  858         lc = LOCK_CLASS(&rm->rm_wlock_object);
  859         db_printf("Backing write-lock (%s):\n", lc->lc_name);
  860         lc->lc_ddb_show(&rm->rm_wlock_object);
  861 }
  862 #endif
  863 
  864 /*
  865  * Read-mostly sleepable locks.
  866  *
  867  * These primitives allow both readers and writers to sleep. However, neither
  868  * readers nor writers are tracked and subsequently there is no priority
  869  * propagation.
  870  *
  871  * They are intended to be only used when write-locking is almost never needed
  872  * (e.g., they can guard against unloading a kernel module) while read-locking
  873  * happens all the time.
  874  *
  875  * Concurrent writers take turns taking the lock while going off cpu. If this is
  876  * of concern for your usecase, this is not the right primitive.
  877  *
  878  * Neither rms_rlock nor rms_runlock use thread fences. Instead interrupt
  879  * fences are inserted to ensure ordering with the code executed in the IPI
  880  * handler.
  881  *
  882  * No attempt is made to track which CPUs read locked at least once,
  883  * consequently write locking sends IPIs to all of them. This will become a
  884  * problem at some point. The easiest way to lessen it is to provide a bitmap.
  885  */
  886 
  887 #define RMS_NOOWNER     ((void *)0x1)
  888 #define RMS_TRANSIENT   ((void *)0x2)
  889 #define RMS_FLAGMASK    0xf
  890 
  891 struct rmslock_pcpu {
  892         int influx;
  893         int readers;
  894 };
  895 
  896 _Static_assert(sizeof(struct rmslock_pcpu) == 8, "bad size");
  897 
  898 /*
  899  * Internal routines
  900  */
  901 static struct rmslock_pcpu *
  902 rms_int_pcpu(struct rmslock *rms)
  903 {
  904 
  905         CRITICAL_ASSERT(curthread);
  906         return (zpcpu_get(rms->pcpu));
  907 }
  908 
  909 static struct rmslock_pcpu *
  910 rms_int_remote_pcpu(struct rmslock *rms, int cpu)
  911 {
  912 
  913         return (zpcpu_get_cpu(rms->pcpu, cpu));
  914 }
  915 
  916 static void
  917 rms_int_influx_enter(struct rmslock *rms, struct rmslock_pcpu *pcpu)
  918 {
  919 
  920         CRITICAL_ASSERT(curthread);
  921         MPASS(pcpu->influx == 0);
  922         pcpu->influx = 1;
  923 }
  924 
  925 static void
  926 rms_int_influx_exit(struct rmslock *rms, struct rmslock_pcpu *pcpu)
  927 {
  928 
  929         CRITICAL_ASSERT(curthread);
  930         MPASS(pcpu->influx == 1);
  931         pcpu->influx = 0;
  932 }
  933 
  934 #ifdef INVARIANTS
  935 static void
  936 rms_int_debug_readers_inc(struct rmslock *rms)
  937 {
  938         int old;
  939         old = atomic_fetchadd_int(&rms->debug_readers, 1);
  940         KASSERT(old >= 0, ("%s: bad readers count %d\n", __func__, old));
  941 }
  942 
  943 static void
  944 rms_int_debug_readers_dec(struct rmslock *rms)
  945 {
  946         int old;
  947 
  948         old = atomic_fetchadd_int(&rms->debug_readers, -1);
  949         KASSERT(old > 0, ("%s: bad readers count %d\n", __func__, old));
  950 }
  951 #else
  952 static void
  953 rms_int_debug_readers_inc(struct rmslock *rms)
  954 {
  955 }
  956 
  957 static void
  958 rms_int_debug_readers_dec(struct rmslock *rms)
  959 {
  960 }
  961 #endif
  962 
  963 static void
  964 rms_int_readers_inc(struct rmslock *rms, struct rmslock_pcpu *pcpu)
  965 {
  966 
  967         CRITICAL_ASSERT(curthread);
  968         rms_int_debug_readers_inc(rms);
  969         pcpu->readers++;
  970 }
  971 
  972 static void
  973 rms_int_readers_dec(struct rmslock *rms, struct rmslock_pcpu *pcpu)
  974 {
  975 
  976         CRITICAL_ASSERT(curthread);
  977         rms_int_debug_readers_dec(rms);
  978         pcpu->readers--;
  979 }
  980 
  981 /*
  982  * Public API
  983  */
  984 void
  985 rms_init(struct rmslock *rms, const char *name)
  986 {
  987 
  988         rms->owner = RMS_NOOWNER;
  989         rms->writers = 0;
  990         rms->readers = 0;
  991         rms->debug_readers = 0;
  992         mtx_init(&rms->mtx, name, NULL, MTX_DEF | MTX_NEW);
  993         rms->pcpu = uma_zalloc_pcpu(pcpu_zone_8, M_WAITOK | M_ZERO);
  994 }
  995 
  996 void
  997 rms_destroy(struct rmslock *rms)
  998 {
  999 
 1000         MPASS(rms->writers == 0);
 1001         MPASS(rms->readers == 0);
 1002         mtx_destroy(&rms->mtx);
 1003         uma_zfree_pcpu(pcpu_zone_8, rms->pcpu);
 1004 }
 1005 
 1006 static void __noinline
 1007 rms_rlock_fallback(struct rmslock *rms)
 1008 {
 1009 
 1010         rms_int_influx_exit(rms, rms_int_pcpu(rms));
 1011         critical_exit();
 1012 
 1013         mtx_lock(&rms->mtx);
 1014         while (rms->writers > 0)
 1015                 msleep(&rms->readers, &rms->mtx, PUSER - 1, mtx_name(&rms->mtx), 0);
 1016         critical_enter();
 1017         rms_int_readers_inc(rms, rms_int_pcpu(rms));
 1018         mtx_unlock(&rms->mtx);
 1019         critical_exit();
 1020         TD_LOCKS_INC(curthread);
 1021 }
 1022 
 1023 void
 1024 rms_rlock(struct rmslock *rms)
 1025 {
 1026         struct rmslock_pcpu *pcpu;
 1027 
 1028         rms_assert_rlock_ok(rms);
 1029         MPASS(atomic_load_ptr(&rms->owner) != curthread);
 1030 
 1031         critical_enter();
 1032         pcpu = rms_int_pcpu(rms);
 1033         rms_int_influx_enter(rms, pcpu);
 1034         atomic_interrupt_fence();
 1035         if (__predict_false(rms->writers > 0)) {
 1036                 rms_rlock_fallback(rms);
 1037                 return;
 1038         }
 1039         atomic_interrupt_fence();
 1040         rms_int_readers_inc(rms, pcpu);
 1041         atomic_interrupt_fence();
 1042         rms_int_influx_exit(rms, pcpu);
 1043         critical_exit();
 1044         TD_LOCKS_INC(curthread);
 1045 }
 1046 
 1047 int
 1048 rms_try_rlock(struct rmslock *rms)
 1049 {
 1050         struct rmslock_pcpu *pcpu;
 1051 
 1052         MPASS(atomic_load_ptr(&rms->owner) != curthread);
 1053 
 1054         critical_enter();
 1055         pcpu = rms_int_pcpu(rms);
 1056         rms_int_influx_enter(rms, pcpu);
 1057         atomic_interrupt_fence();
 1058         if (__predict_false(rms->writers > 0)) {
 1059                 rms_int_influx_exit(rms, pcpu);
 1060                 critical_exit();
 1061                 return (0);
 1062         }
 1063         atomic_interrupt_fence();
 1064         rms_int_readers_inc(rms, pcpu);
 1065         atomic_interrupt_fence();
 1066         rms_int_influx_exit(rms, pcpu);
 1067         critical_exit();
 1068         TD_LOCKS_INC(curthread);
 1069         return (1);
 1070 }
 1071 
 1072 static void __noinline
 1073 rms_runlock_fallback(struct rmslock *rms)
 1074 {
 1075 
 1076         rms_int_influx_exit(rms, rms_int_pcpu(rms));
 1077         critical_exit();
 1078 
 1079         mtx_lock(&rms->mtx);
 1080         MPASS(rms->writers > 0);
 1081         MPASS(rms->readers > 0);
 1082         MPASS(rms->debug_readers == rms->readers);
 1083         rms_int_debug_readers_dec(rms);
 1084         rms->readers--;
 1085         if (rms->readers == 0)
 1086                 wakeup_one(&rms->writers);
 1087         mtx_unlock(&rms->mtx);
 1088         TD_LOCKS_DEC(curthread);
 1089 }
 1090 
 1091 void
 1092 rms_runlock(struct rmslock *rms)
 1093 {
 1094         struct rmslock_pcpu *pcpu;
 1095 
 1096         critical_enter();
 1097         pcpu = rms_int_pcpu(rms);
 1098         rms_int_influx_enter(rms, pcpu);
 1099         atomic_interrupt_fence();
 1100         if (__predict_false(rms->writers > 0)) {
 1101                 rms_runlock_fallback(rms);
 1102                 return;
 1103         }
 1104         atomic_interrupt_fence();
 1105         rms_int_readers_dec(rms, pcpu);
 1106         atomic_interrupt_fence();
 1107         rms_int_influx_exit(rms, pcpu);
 1108         critical_exit();
 1109         TD_LOCKS_DEC(curthread);
 1110 }
 1111 
 1112 struct rmslock_ipi {
 1113         struct rmslock *rms;
 1114         struct smp_rendezvous_cpus_retry_arg srcra;
 1115 };
 1116 
 1117 static void
 1118 rms_action_func(void *arg)
 1119 {
 1120         struct rmslock_ipi *rmsipi;
 1121         struct rmslock_pcpu *pcpu;
 1122         struct rmslock *rms;
 1123 
 1124         rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
 1125         rms = rmsipi->rms;
 1126         pcpu = rms_int_pcpu(rms);
 1127 
 1128         if (pcpu->influx)
 1129                 return;
 1130         if (pcpu->readers != 0) {
 1131                 atomic_add_int(&rms->readers, pcpu->readers);
 1132                 pcpu->readers = 0;
 1133         }
 1134         smp_rendezvous_cpus_done(arg);
 1135 }
 1136 
 1137 static void
 1138 rms_wait_func(void *arg, int cpu)
 1139 {
 1140         struct rmslock_ipi *rmsipi;
 1141         struct rmslock_pcpu *pcpu;
 1142         struct rmslock *rms;
 1143 
 1144         rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
 1145         rms = rmsipi->rms;
 1146         pcpu = rms_int_remote_pcpu(rms, cpu);
 1147 
 1148         while (atomic_load_int(&pcpu->influx))
 1149                 cpu_spinwait();
 1150 }
 1151 
 1152 #ifdef INVARIANTS
 1153 static void
 1154 rms_assert_no_pcpu_readers(struct rmslock *rms)
 1155 {
 1156         struct rmslock_pcpu *pcpu;
 1157         int cpu;
 1158 
 1159         CPU_FOREACH(cpu) {
 1160                 pcpu = rms_int_remote_pcpu(rms, cpu);
 1161                 if (pcpu->readers != 0) {
 1162                         panic("%s: got %d readers on cpu %d\n", __func__,
 1163                             pcpu->readers, cpu);
 1164                 }
 1165         }
 1166 }
 1167 #else
 1168 static void
 1169 rms_assert_no_pcpu_readers(struct rmslock *rms)
 1170 {
 1171 }
 1172 #endif
 1173 
 1174 static void
 1175 rms_wlock_switch(struct rmslock *rms)
 1176 {
 1177         struct rmslock_ipi rmsipi;
 1178 
 1179         MPASS(rms->readers == 0);
 1180         MPASS(rms->writers == 1);
 1181 
 1182         rmsipi.rms = rms;
 1183 
 1184         smp_rendezvous_cpus_retry(all_cpus,
 1185             smp_no_rendezvous_barrier,
 1186             rms_action_func,
 1187             smp_no_rendezvous_barrier,
 1188             rms_wait_func,
 1189             &rmsipi.srcra);
 1190 }
 1191 
 1192 void
 1193 rms_wlock(struct rmslock *rms)
 1194 {
 1195 
 1196         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
 1197         MPASS(atomic_load_ptr(&rms->owner) != curthread);
 1198 
 1199         mtx_lock(&rms->mtx);
 1200         rms->writers++;
 1201         if (rms->writers > 1) {
 1202                 msleep(&rms->owner, &rms->mtx, (PUSER - 1),
 1203                     mtx_name(&rms->mtx), 0);
 1204                 MPASS(rms->readers == 0);
 1205                 KASSERT(rms->owner == RMS_TRANSIENT,
 1206                     ("%s: unexpected owner value %p\n", __func__,
 1207                     rms->owner));
 1208                 goto out_grab;
 1209         }
 1210 
 1211         KASSERT(rms->owner == RMS_NOOWNER,
 1212             ("%s: unexpected owner value %p\n", __func__, rms->owner));
 1213 
 1214         rms_wlock_switch(rms);
 1215         rms_assert_no_pcpu_readers(rms);
 1216 
 1217         if (rms->readers > 0) {
 1218                 msleep(&rms->writers, &rms->mtx, (PUSER - 1),
 1219                     mtx_name(&rms->mtx), 0);
 1220         }
 1221 
 1222 out_grab:
 1223         rms->owner = curthread;
 1224         rms_assert_no_pcpu_readers(rms);
 1225         mtx_unlock(&rms->mtx);
 1226         MPASS(rms->readers == 0);
 1227         TD_LOCKS_INC(curthread);
 1228 }
 1229 
 1230 void
 1231 rms_wunlock(struct rmslock *rms)
 1232 {
 1233 
 1234         mtx_lock(&rms->mtx);
 1235         KASSERT(rms->owner == curthread,
 1236             ("%s: unexpected owner value %p\n", __func__, rms->owner));
 1237         MPASS(rms->writers >= 1);
 1238         MPASS(rms->readers == 0);
 1239         rms->writers--;
 1240         if (rms->writers > 0) {
 1241                 wakeup_one(&rms->owner);
 1242                 rms->owner = RMS_TRANSIENT;
 1243         } else {
 1244                 wakeup(&rms->readers);
 1245                 rms->owner = RMS_NOOWNER;
 1246         }
 1247         mtx_unlock(&rms->mtx);
 1248         TD_LOCKS_DEC(curthread);
 1249 }
 1250 
 1251 void
 1252 rms_unlock(struct rmslock *rms)
 1253 {
 1254 
 1255         if (rms_wowned(rms))
 1256                 rms_wunlock(rms);
 1257         else
 1258                 rms_runlock(rms);
 1259 }
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FreeBSD/Linux Kernel Cross Reference sys/kern/kern_rmlock.c

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