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

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    1 /*-
    2  * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
    3  *
    4  * Redistribution and use in source and binary forms, with or without
    5  * modification, are permitted provided that the following conditions
    6  * are met:
    7  * 1. Redistributions of source code must retain the above copyright
    8  *    notice, this list of conditions and the following disclaimer.
    9  * 2. Redistributions in binary form must reproduce the above copyright
   10  *    notice, this list of conditions and the following disclaimer in the
   11  *    documentation and/or other materials provided with the distribution.
   12  * 3. Berkeley Software Design Inc's name may not be used to endorse or
   13  *    promote products derived from this software without specific prior
   14  *    written permission.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
   17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   19  * ARE DISCLAIMED.  IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
   20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   26  * SUCH DAMAGE.
   27  *
   28  *      from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
   29  *      and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
   30  */
   31 
   32 /*
   33  * Machine independent bits of mutex implementation.
   34  */
   35 
   36 #include <sys/cdefs.h>
   37 __FBSDID("$FreeBSD: releng/10.2/sys/kern/kern_mutex.c 285759 2015-07-21 17:16:37Z markj $");
   38 
   39 #include "opt_adaptive_mutexes.h"
   40 #include "opt_ddb.h"
   41 #include "opt_global.h"
   42 #include "opt_hwpmc_hooks.h"
   43 #include "opt_kdtrace.h"
   44 #include "opt_sched.h"
   45 
   46 #include <sys/param.h>
   47 #include <sys/systm.h>
   48 #include <sys/bus.h>
   49 #include <sys/conf.h>
   50 #include <sys/kdb.h>
   51 #include <sys/kernel.h>
   52 #include <sys/ktr.h>
   53 #include <sys/lock.h>
   54 #include <sys/malloc.h>
   55 #include <sys/mutex.h>
   56 #include <sys/proc.h>
   57 #include <sys/resourcevar.h>
   58 #include <sys/sched.h>
   59 #include <sys/sbuf.h>
   60 #include <sys/sysctl.h>
   61 #include <sys/turnstile.h>
   62 #include <sys/vmmeter.h>
   63 #include <sys/lock_profile.h>
   64 
   65 #include <machine/atomic.h>
   66 #include <machine/bus.h>
   67 #include <machine/cpu.h>
   68 
   69 #include <ddb/ddb.h>
   70 
   71 #include <fs/devfs/devfs_int.h>
   72 
   73 #include <vm/vm.h>
   74 #include <vm/vm_extern.h>
   75 
   76 #if defined(SMP) && !defined(NO_ADAPTIVE_MUTEXES)
   77 #define ADAPTIVE_MUTEXES
   78 #endif
   79 
   80 #ifdef HWPMC_HOOKS
   81 #include <sys/pmckern.h>
   82 PMC_SOFT_DEFINE( , , lock, failed);
   83 #endif
   84 
   85 /*
   86  * Return the mutex address when the lock cookie address is provided.
   87  * This functionality assumes that struct mtx* have a member named mtx_lock.
   88  */
   89 #define mtxlock2mtx(c)  (__containerof(c, struct mtx, mtx_lock))
   90 
   91 /*
   92  * Internal utility macros.
   93  */
   94 #define mtx_unowned(m)  ((m)->mtx_lock == MTX_UNOWNED)
   95 
   96 #define mtx_destroyed(m) ((m)->mtx_lock == MTX_DESTROYED)
   97 
   98 #define mtx_owner(m)    ((struct thread *)((m)->mtx_lock & ~MTX_FLAGMASK))
   99 
  100 static void     assert_mtx(const struct lock_object *lock, int what);
  101 #ifdef DDB
  102 static void     db_show_mtx(const struct lock_object *lock);
  103 #endif
  104 static void     lock_mtx(struct lock_object *lock, uintptr_t how);
  105 static void     lock_spin(struct lock_object *lock, uintptr_t how);
  106 #ifdef KDTRACE_HOOKS
  107 static int      owner_mtx(const struct lock_object *lock,
  108                     struct thread **owner);
  109 #endif
  110 static uintptr_t unlock_mtx(struct lock_object *lock);
  111 static uintptr_t unlock_spin(struct lock_object *lock);
  112 
  113 /*
  114  * Lock classes for sleep and spin mutexes.
  115  */
  116 struct lock_class lock_class_mtx_sleep = {
  117         .lc_name = "sleep mutex",
  118         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
  119         .lc_assert = assert_mtx,
  120 #ifdef DDB
  121         .lc_ddb_show = db_show_mtx,
  122 #endif
  123         .lc_lock = lock_mtx,
  124         .lc_unlock = unlock_mtx,
  125 #ifdef KDTRACE_HOOKS
  126         .lc_owner = owner_mtx,
  127 #endif
  128 };
  129 struct lock_class lock_class_mtx_spin = {
  130         .lc_name = "spin mutex",
  131         .lc_flags = LC_SPINLOCK | LC_RECURSABLE,
  132         .lc_assert = assert_mtx,
  133 #ifdef DDB
  134         .lc_ddb_show = db_show_mtx,
  135 #endif
  136         .lc_lock = lock_spin,
  137         .lc_unlock = unlock_spin,
  138 #ifdef KDTRACE_HOOKS
  139         .lc_owner = owner_mtx,
  140 #endif
  141 };
  142 
  143 /*
  144  * System-wide mutexes
  145  */
  146 struct mtx blocked_lock;
  147 struct mtx Giant;
  148 
  149 void
  150 assert_mtx(const struct lock_object *lock, int what)
  151 {
  152 
  153         mtx_assert((const struct mtx *)lock, what);
  154 }
  155 
  156 void
  157 lock_mtx(struct lock_object *lock, uintptr_t how)
  158 {
  159 
  160         mtx_lock((struct mtx *)lock);
  161 }
  162 
  163 void
  164 lock_spin(struct lock_object *lock, uintptr_t how)
  165 {
  166 
  167         panic("spin locks can only use msleep_spin");
  168 }
  169 
  170 uintptr_t
  171 unlock_mtx(struct lock_object *lock)
  172 {
  173         struct mtx *m;
  174 
  175         m = (struct mtx *)lock;
  176         mtx_assert(m, MA_OWNED | MA_NOTRECURSED);
  177         mtx_unlock(m);
  178         return (0);
  179 }
  180 
  181 uintptr_t
  182 unlock_spin(struct lock_object *lock)
  183 {
  184 
  185         panic("spin locks can only use msleep_spin");
  186 }
  187 
  188 #ifdef KDTRACE_HOOKS
  189 int
  190 owner_mtx(const struct lock_object *lock, struct thread **owner)
  191 {
  192         const struct mtx *m = (const struct mtx *)lock;
  193 
  194         *owner = mtx_owner(m);
  195         return (mtx_unowned(m) == 0);
  196 }
  197 #endif
  198 
  199 /*
  200  * Function versions of the inlined __mtx_* macros.  These are used by
  201  * modules and can also be called from assembly language if needed.
  202  */
  203 void
  204 __mtx_lock_flags(volatile uintptr_t *c, int opts, const char *file, int line)
  205 {
  206         struct mtx *m;
  207 
  208         if (SCHEDULER_STOPPED())
  209                 return;
  210 
  211         m = mtxlock2mtx(c);
  212 
  213         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  214             ("mtx_lock() by idle thread %p on sleep mutex %s @ %s:%d",
  215             curthread, m->lock_object.lo_name, file, line));
  216         KASSERT(m->mtx_lock != MTX_DESTROYED,
  217             ("mtx_lock() of destroyed mutex @ %s:%d", file, line));
  218         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
  219             ("mtx_lock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
  220             file, line));
  221         WITNESS_CHECKORDER(&m->lock_object, (opts & ~MTX_RECURSE) |
  222             LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL);
  223 
  224         __mtx_lock(m, curthread, opts, file, line);
  225         LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
  226             line);
  227         WITNESS_LOCK(&m->lock_object, (opts & ~MTX_RECURSE) | LOP_EXCLUSIVE,
  228             file, line);
  229         curthread->td_locks++;
  230 }
  231 
  232 void
  233 __mtx_unlock_flags(volatile uintptr_t *c, int opts, const char *file, int line)
  234 {
  235         struct mtx *m;
  236 
  237         if (SCHEDULER_STOPPED())
  238                 return;
  239 
  240         m = mtxlock2mtx(c);
  241 
  242         KASSERT(m->mtx_lock != MTX_DESTROYED,
  243             ("mtx_unlock() of destroyed mutex @ %s:%d", file, line));
  244         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
  245             ("mtx_unlock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
  246             file, line));
  247         WITNESS_UNLOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  248         LOCK_LOG_LOCK("UNLOCK", &m->lock_object, opts, m->mtx_recurse, file,
  249             line);
  250         mtx_assert(m, MA_OWNED);
  251 
  252         if (m->mtx_recurse == 0)
  253                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_MTX_UNLOCK_RELEASE, m);
  254         __mtx_unlock(m, curthread, opts, file, line);
  255         curthread->td_locks--;
  256 }
  257 
  258 void
  259 __mtx_lock_spin_flags(volatile uintptr_t *c, int opts, const char *file,
  260     int line)
  261 {
  262         struct mtx *m;
  263 
  264         if (SCHEDULER_STOPPED())
  265                 return;
  266 
  267         m = mtxlock2mtx(c);
  268 
  269         KASSERT(m->mtx_lock != MTX_DESTROYED,
  270             ("mtx_lock_spin() of destroyed mutex @ %s:%d", file, line));
  271         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
  272             ("mtx_lock_spin() of sleep mutex %s @ %s:%d",
  273             m->lock_object.lo_name, file, line));
  274         if (mtx_owned(m))
  275                 KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0 ||
  276                     (opts & MTX_RECURSE) != 0,
  277             ("mtx_lock_spin: recursed on non-recursive mutex %s @ %s:%d\n",
  278                     m->lock_object.lo_name, file, line));
  279         opts &= ~MTX_RECURSE;
  280         WITNESS_CHECKORDER(&m->lock_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE,
  281             file, line, NULL);
  282         __mtx_lock_spin(m, curthread, opts, file, line);
  283         LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
  284             line);
  285         WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  286 }
  287 
  288 void
  289 __mtx_unlock_spin_flags(volatile uintptr_t *c, int opts, const char *file,
  290     int line)
  291 {
  292         struct mtx *m;
  293 
  294         if (SCHEDULER_STOPPED())
  295                 return;
  296 
  297         m = mtxlock2mtx(c);
  298 
  299         KASSERT(m->mtx_lock != MTX_DESTROYED,
  300             ("mtx_unlock_spin() of destroyed mutex @ %s:%d", file, line));
  301         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
  302             ("mtx_unlock_spin() of sleep mutex %s @ %s:%d",
  303             m->lock_object.lo_name, file, line));
  304         WITNESS_UNLOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  305         LOCK_LOG_LOCK("UNLOCK", &m->lock_object, opts, m->mtx_recurse, file,
  306             line);
  307         mtx_assert(m, MA_OWNED);
  308 
  309         __mtx_unlock_spin(m);
  310 }
  311 
  312 /*
  313  * The important part of mtx_trylock{,_flags}()
  314  * Tries to acquire lock `m.'  If this function is called on a mutex that
  315  * is already owned, it will recursively acquire the lock.
  316  */
  317 int
  318 _mtx_trylock_flags_(volatile uintptr_t *c, int opts, const char *file, int line)
  319 {
  320         struct mtx *m;
  321 #ifdef LOCK_PROFILING
  322         uint64_t waittime = 0;
  323         int contested = 0;
  324 #endif
  325         int rval;
  326 
  327         if (SCHEDULER_STOPPED())
  328                 return (1);
  329 
  330         m = mtxlock2mtx(c);
  331 
  332         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  333             ("mtx_trylock() by idle thread %p on sleep mutex %s @ %s:%d",
  334             curthread, m->lock_object.lo_name, file, line));
  335         KASSERT(m->mtx_lock != MTX_DESTROYED,
  336             ("mtx_trylock() of destroyed mutex @ %s:%d", file, line));
  337         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
  338             ("mtx_trylock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
  339             file, line));
  340 
  341         if (mtx_owned(m) && ((m->lock_object.lo_flags & LO_RECURSABLE) != 0 ||
  342             (opts & MTX_RECURSE) != 0)) {
  343                 m->mtx_recurse++;
  344                 atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
  345                 rval = 1;
  346         } else
  347                 rval = _mtx_obtain_lock(m, (uintptr_t)curthread);
  348         opts &= ~MTX_RECURSE;
  349 
  350         LOCK_LOG_TRY("LOCK", &m->lock_object, opts, rval, file, line);
  351         if (rval) {
  352                 WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE | LOP_TRYLOCK,
  353                     file, line);
  354                 curthread->td_locks++;
  355                 if (m->mtx_recurse == 0)
  356                         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_LOCK_ACQUIRE,
  357                             m, contested, waittime, file, line);
  358 
  359         }
  360 
  361         return (rval);
  362 }
  363 
  364 /*
  365  * __mtx_lock_sleep: the tougher part of acquiring an MTX_DEF lock.
  366  *
  367  * We call this if the lock is either contested (i.e. we need to go to
  368  * sleep waiting for it), or if we need to recurse on it.
  369  */
  370 void
  371 __mtx_lock_sleep(volatile uintptr_t *c, uintptr_t tid, int opts,
  372     const char *file, int line)
  373 {
  374         struct mtx *m;
  375         struct turnstile *ts;
  376         uintptr_t v;
  377 #ifdef ADAPTIVE_MUTEXES
  378         volatile struct thread *owner;
  379 #endif
  380 #ifdef KTR
  381         int cont_logged = 0;
  382 #endif
  383 #ifdef LOCK_PROFILING
  384         int contested = 0;
  385         uint64_t waittime = 0;
  386 #endif
  387 #ifdef KDTRACE_HOOKS
  388         uint64_t spin_cnt = 0;
  389         uint64_t sleep_cnt = 0;
  390         int64_t sleep_time = 0;
  391         int64_t all_time = 0;
  392 #endif
  393 
  394         if (SCHEDULER_STOPPED())
  395                 return;
  396 
  397         m = mtxlock2mtx(c);
  398 
  399         if (mtx_owned(m)) {
  400                 KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0 ||
  401                     (opts & MTX_RECURSE) != 0,
  402             ("_mtx_lock_sleep: recursed on non-recursive mutex %s @ %s:%d\n",
  403                     m->lock_object.lo_name, file, line));
  404                 opts &= ~MTX_RECURSE;
  405                 m->mtx_recurse++;
  406                 atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
  407                 if (LOCK_LOG_TEST(&m->lock_object, opts))
  408                         CTR1(KTR_LOCK, "_mtx_lock_sleep: %p recursing", m);
  409                 return;
  410         }
  411         opts &= ~MTX_RECURSE;
  412 
  413 #ifdef HWPMC_HOOKS
  414         PMC_SOFT_CALL( , , lock, failed);
  415 #endif
  416         lock_profile_obtain_lock_failed(&m->lock_object,
  417                     &contested, &waittime);
  418         if (LOCK_LOG_TEST(&m->lock_object, opts))
  419                 CTR4(KTR_LOCK,
  420                     "_mtx_lock_sleep: %s contested (lock=%p) at %s:%d",
  421                     m->lock_object.lo_name, (void *)m->mtx_lock, file, line);
  422 #ifdef KDTRACE_HOOKS
  423         all_time -= lockstat_nsecs(&m->lock_object);
  424 #endif
  425 
  426         while (!_mtx_obtain_lock(m, tid)) {
  427 #ifdef KDTRACE_HOOKS
  428                 spin_cnt++;
  429 #endif
  430 #ifdef ADAPTIVE_MUTEXES
  431                 /*
  432                  * If the owner is running on another CPU, spin until the
  433                  * owner stops running or the state of the lock changes.
  434                  */
  435                 v = m->mtx_lock;
  436                 if (v != MTX_UNOWNED) {
  437                         owner = (struct thread *)(v & ~MTX_FLAGMASK);
  438                         if (TD_IS_RUNNING(owner)) {
  439                                 if (LOCK_LOG_TEST(&m->lock_object, 0))
  440                                         CTR3(KTR_LOCK,
  441                                             "%s: spinning on %p held by %p",
  442                                             __func__, m, owner);
  443                                 KTR_STATE1(KTR_SCHED, "thread",
  444                                     sched_tdname((struct thread *)tid),
  445                                     "spinning", "lockname:\"%s\"",
  446                                     m->lock_object.lo_name);
  447                                 while (mtx_owner(m) == owner &&
  448                                     TD_IS_RUNNING(owner)) {
  449                                         cpu_spinwait();
  450 #ifdef KDTRACE_HOOKS
  451                                         spin_cnt++;
  452 #endif
  453                                 }
  454                                 KTR_STATE0(KTR_SCHED, "thread",
  455                                     sched_tdname((struct thread *)tid),
  456                                     "running");
  457                                 continue;
  458                         }
  459                 }
  460 #endif
  461 
  462                 ts = turnstile_trywait(&m->lock_object);
  463                 v = m->mtx_lock;
  464 
  465                 /*
  466                  * Check if the lock has been released while spinning for
  467                  * the turnstile chain lock.
  468                  */
  469                 if (v == MTX_UNOWNED) {
  470                         turnstile_cancel(ts);
  471                         continue;
  472                 }
  473 
  474 #ifdef ADAPTIVE_MUTEXES
  475                 /*
  476                  * The current lock owner might have started executing
  477                  * on another CPU (or the lock could have changed
  478                  * owners) while we were waiting on the turnstile
  479                  * chain lock.  If so, drop the turnstile lock and try
  480                  * again.
  481                  */
  482                 owner = (struct thread *)(v & ~MTX_FLAGMASK);
  483                 if (TD_IS_RUNNING(owner)) {
  484                         turnstile_cancel(ts);
  485                         continue;
  486                 }
  487 #endif
  488 
  489                 /*
  490                  * If the mutex isn't already contested and a failure occurs
  491                  * setting the contested bit, the mutex was either released
  492                  * or the state of the MTX_RECURSED bit changed.
  493                  */
  494                 if ((v & MTX_CONTESTED) == 0 &&
  495                     !atomic_cmpset_ptr(&m->mtx_lock, v, v | MTX_CONTESTED)) {
  496                         turnstile_cancel(ts);
  497                         continue;
  498                 }
  499 
  500                 /*
  501                  * We definitely must sleep for this lock.
  502                  */
  503                 mtx_assert(m, MA_NOTOWNED);
  504 
  505 #ifdef KTR
  506                 if (!cont_logged) {
  507                         CTR6(KTR_CONTENTION,
  508                             "contention: %p at %s:%d wants %s, taken by %s:%d",
  509                             (void *)tid, file, line, m->lock_object.lo_name,
  510                             WITNESS_FILE(&m->lock_object),
  511                             WITNESS_LINE(&m->lock_object));
  512                         cont_logged = 1;
  513                 }
  514 #endif
  515 
  516                 /*
  517                  * Block on the turnstile.
  518                  */
  519 #ifdef KDTRACE_HOOKS
  520                 sleep_time -= lockstat_nsecs(&m->lock_object);
  521 #endif
  522                 turnstile_wait(ts, mtx_owner(m), TS_EXCLUSIVE_QUEUE);
  523 #ifdef KDTRACE_HOOKS
  524                 sleep_time += lockstat_nsecs(&m->lock_object);
  525                 sleep_cnt++;
  526 #endif
  527         }
  528 #ifdef KDTRACE_HOOKS
  529         all_time += lockstat_nsecs(&m->lock_object);
  530 #endif
  531 #ifdef KTR
  532         if (cont_logged) {
  533                 CTR4(KTR_CONTENTION,
  534                     "contention end: %s acquired by %p at %s:%d",
  535                     m->lock_object.lo_name, (void *)tid, file, line);
  536         }
  537 #endif
  538         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_LOCK_ACQUIRE, m, contested,
  539             waittime, file, line);
  540 #ifdef KDTRACE_HOOKS
  541         if (sleep_time)
  542                 LOCKSTAT_RECORD1(LS_MTX_LOCK_BLOCK, m, sleep_time);
  543 
  544         /*
  545          * Only record the loops spinning and not sleeping. 
  546          */
  547         if (spin_cnt > sleep_cnt)
  548                 LOCKSTAT_RECORD1(LS_MTX_LOCK_SPIN, m, (all_time - sleep_time));
  549 #endif
  550 }
  551 
  552 static void
  553 _mtx_lock_spin_failed(struct mtx *m)
  554 {
  555         struct thread *td;
  556 
  557         td = mtx_owner(m);
  558 
  559         /* If the mutex is unlocked, try again. */
  560         if (td == NULL)
  561                 return;
  562 
  563         printf( "spin lock %p (%s) held by %p (tid %d) too long\n",
  564             m, m->lock_object.lo_name, td, td->td_tid);
  565 #ifdef WITNESS
  566         witness_display_spinlock(&m->lock_object, td, printf);
  567 #endif
  568         panic("spin lock held too long");
  569 }
  570 
  571 #ifdef SMP
  572 /*
  573  * _mtx_lock_spin_cookie: the tougher part of acquiring an MTX_SPIN lock.
  574  *
  575  * This is only called if we need to actually spin for the lock. Recursion
  576  * is handled inline.
  577  */
  578 void
  579 _mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t tid, int opts,
  580     const char *file, int line)
  581 {
  582         struct mtx *m;
  583         int i = 0;
  584 #ifdef LOCK_PROFILING
  585         int contested = 0;
  586         uint64_t waittime = 0;
  587 #endif
  588 #ifdef KDTRACE_HOOKS
  589         int64_t spin_time = 0;
  590 #endif
  591 
  592         if (SCHEDULER_STOPPED())
  593                 return;
  594 
  595         m = mtxlock2mtx(c);
  596 
  597         if (LOCK_LOG_TEST(&m->lock_object, opts))
  598                 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
  599         KTR_STATE1(KTR_SCHED, "thread", sched_tdname((struct thread *)tid),
  600             "spinning", "lockname:\"%s\"", m->lock_object.lo_name);
  601 
  602 #ifdef HWPMC_HOOKS
  603         PMC_SOFT_CALL( , , lock, failed);
  604 #endif
  605         lock_profile_obtain_lock_failed(&m->lock_object, &contested, &waittime);
  606 #ifdef KDTRACE_HOOKS
  607         spin_time -= lockstat_nsecs(&m->lock_object);
  608 #endif
  609         while (!_mtx_obtain_lock(m, tid)) {
  610 
  611                 /* Give interrupts a chance while we spin. */
  612                 spinlock_exit();
  613                 while (m->mtx_lock != MTX_UNOWNED) {
  614                         if (i++ < 10000000) {
  615                                 cpu_spinwait();
  616                                 continue;
  617                         }
  618                         if (i < 60000000 || kdb_active || panicstr != NULL)
  619                                 DELAY(1);
  620                         else
  621                                 _mtx_lock_spin_failed(m);
  622                         cpu_spinwait();
  623                 }
  624                 spinlock_enter();
  625         }
  626 #ifdef KDTRACE_HOOKS
  627         spin_time += lockstat_nsecs(&m->lock_object);
  628 #endif
  629 
  630         if (LOCK_LOG_TEST(&m->lock_object, opts))
  631                 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spin done", m);
  632         KTR_STATE0(KTR_SCHED, "thread", sched_tdname((struct thread *)tid),
  633             "running");
  634 
  635         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_SPIN_LOCK_ACQUIRE, m,
  636             contested, waittime, (file), (line));
  637 #ifdef KDTRACE_HOOKS
  638         if (spin_time != 0)
  639                 LOCKSTAT_RECORD1(LS_MTX_SPIN_LOCK_SPIN, m, spin_time);
  640 #endif
  641 }
  642 #endif /* SMP */
  643 
  644 void
  645 thread_lock_flags_(struct thread *td, int opts, const char *file, int line)
  646 {
  647         struct mtx *m;
  648         uintptr_t tid;
  649         int i;
  650 #ifdef LOCK_PROFILING
  651         int contested = 0;
  652         uint64_t waittime = 0;
  653 #endif
  654 #ifdef KDTRACE_HOOKS
  655         int64_t spin_time = 0;
  656 #endif
  657 
  658         i = 0;
  659         tid = (uintptr_t)curthread;
  660 
  661         if (SCHEDULER_STOPPED())
  662                 return;
  663 
  664 #ifdef KDTRACE_HOOKS
  665         spin_time -= lockstat_nsecs(&td->td_lock->lock_object);
  666 #endif
  667         for (;;) {
  668 retry:
  669                 spinlock_enter();
  670                 m = td->td_lock;
  671                 KASSERT(m->mtx_lock != MTX_DESTROYED,
  672                     ("thread_lock() of destroyed mutex @ %s:%d", file, line));
  673                 KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
  674                     ("thread_lock() of sleep mutex %s @ %s:%d",
  675                     m->lock_object.lo_name, file, line));
  676                 if (mtx_owned(m))
  677                         KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0,
  678             ("thread_lock: recursed on non-recursive mutex %s @ %s:%d\n",
  679                             m->lock_object.lo_name, file, line));
  680                 WITNESS_CHECKORDER(&m->lock_object,
  681                     opts | LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL);
  682                 while (!_mtx_obtain_lock(m, tid)) {
  683                         if (m->mtx_lock == tid) {
  684                                 m->mtx_recurse++;
  685                                 break;
  686                         }
  687 #ifdef HWPMC_HOOKS
  688                         PMC_SOFT_CALL( , , lock, failed);
  689 #endif
  690                         lock_profile_obtain_lock_failed(&m->lock_object,
  691                             &contested, &waittime);
  692                         /* Give interrupts a chance while we spin. */
  693                         spinlock_exit();
  694                         while (m->mtx_lock != MTX_UNOWNED) {
  695                                 if (i++ < 10000000)
  696                                         cpu_spinwait();
  697                                 else if (i < 60000000 ||
  698                                     kdb_active || panicstr != NULL)
  699                                         DELAY(1);
  700                                 else
  701                                         _mtx_lock_spin_failed(m);
  702                                 cpu_spinwait();
  703                                 if (m != td->td_lock)
  704                                         goto retry;
  705                         }
  706                         spinlock_enter();
  707                 }
  708                 if (m == td->td_lock)
  709                         break;
  710                 __mtx_unlock_spin(m);   /* does spinlock_exit() */
  711         }
  712 #ifdef KDTRACE_HOOKS
  713         spin_time += lockstat_nsecs(&m->lock_object);
  714 #endif
  715         if (m->mtx_recurse == 0)
  716                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_SPIN_LOCK_ACQUIRE,
  717                     m, contested, waittime, (file), (line));
  718         LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
  719             line);
  720         WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  721         LOCKSTAT_RECORD1(LS_THREAD_LOCK_SPIN, m, spin_time);
  722 }
  723 
  724 struct mtx *
  725 thread_lock_block(struct thread *td)
  726 {
  727         struct mtx *lock;
  728 
  729         THREAD_LOCK_ASSERT(td, MA_OWNED);
  730         lock = td->td_lock;
  731         td->td_lock = &blocked_lock;
  732         mtx_unlock_spin(lock);
  733 
  734         return (lock);
  735 }
  736 
  737 void
  738 thread_lock_unblock(struct thread *td, struct mtx *new)
  739 {
  740         mtx_assert(new, MA_OWNED);
  741         MPASS(td->td_lock == &blocked_lock);
  742         atomic_store_rel_ptr((volatile void *)&td->td_lock, (uintptr_t)new);
  743 }
  744 
  745 void
  746 thread_lock_set(struct thread *td, struct mtx *new)
  747 {
  748         struct mtx *lock;
  749 
  750         mtx_assert(new, MA_OWNED);
  751         THREAD_LOCK_ASSERT(td, MA_OWNED);
  752         lock = td->td_lock;
  753         td->td_lock = new;
  754         mtx_unlock_spin(lock);
  755 }
  756 
  757 /*
  758  * __mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock.
  759  *
  760  * We are only called here if the lock is recursed or contested (i.e. we
  761  * need to wake up a blocked thread).
  762  */
  763 void
  764 __mtx_unlock_sleep(volatile uintptr_t *c, int opts, const char *file, int line)
  765 {
  766         struct mtx *m;
  767         struct turnstile *ts;
  768 
  769         if (SCHEDULER_STOPPED())
  770                 return;
  771 
  772         m = mtxlock2mtx(c);
  773 
  774         if (mtx_recursed(m)) {
  775                 if (--(m->mtx_recurse) == 0)
  776                         atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED);
  777                 if (LOCK_LOG_TEST(&m->lock_object, opts))
  778                         CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p unrecurse", m);
  779                 return;
  780         }
  781 
  782         /*
  783          * We have to lock the chain before the turnstile so this turnstile
  784          * can be removed from the hash list if it is empty.
  785          */
  786         turnstile_chain_lock(&m->lock_object);
  787         ts = turnstile_lookup(&m->lock_object);
  788         if (LOCK_LOG_TEST(&m->lock_object, opts))
  789                 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
  790         MPASS(ts != NULL);
  791         turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE);
  792         _mtx_release_lock_quick(m);
  793 
  794         /*
  795          * This turnstile is now no longer associated with the mutex.  We can
  796          * unlock the chain lock so a new turnstile may take it's place.
  797          */
  798         turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
  799         turnstile_chain_unlock(&m->lock_object);
  800 }
  801 
  802 /*
  803  * All the unlocking of MTX_SPIN locks is done inline.
  804  * See the __mtx_unlock_spin() macro for the details.
  805  */
  806 
  807 /*
  808  * The backing function for the INVARIANTS-enabled mtx_assert()
  809  */
  810 #ifdef INVARIANT_SUPPORT
  811 void
  812 __mtx_assert(const volatile uintptr_t *c, int what, const char *file, int line)
  813 {
  814         const struct mtx *m;
  815 
  816         if (panicstr != NULL || dumping)
  817                 return;
  818 
  819         m = mtxlock2mtx(c);
  820 
  821         switch (what) {
  822         case MA_OWNED:
  823         case MA_OWNED | MA_RECURSED:
  824         case MA_OWNED | MA_NOTRECURSED:
  825                 if (!mtx_owned(m))
  826                         panic("mutex %s not owned at %s:%d",
  827                             m->lock_object.lo_name, file, line);
  828                 if (mtx_recursed(m)) {
  829                         if ((what & MA_NOTRECURSED) != 0)
  830                                 panic("mutex %s recursed at %s:%d",
  831                                     m->lock_object.lo_name, file, line);
  832                 } else if ((what & MA_RECURSED) != 0) {
  833                         panic("mutex %s unrecursed at %s:%d",
  834                             m->lock_object.lo_name, file, line);
  835                 }
  836                 break;
  837         case MA_NOTOWNED:
  838                 if (mtx_owned(m))
  839                         panic("mutex %s owned at %s:%d",
  840                             m->lock_object.lo_name, file, line);
  841                 break;
  842         default:
  843                 panic("unknown mtx_assert at %s:%d", file, line);
  844         }
  845 }
  846 #endif
  847 
  848 /*
  849  * The MUTEX_DEBUG-enabled mtx_validate()
  850  *
  851  * Most of these checks have been moved off into the LO_INITIALIZED flag
  852  * maintained by the witness code.
  853  */
  854 #ifdef MUTEX_DEBUG
  855 
  856 void    mtx_validate(struct mtx *);
  857 
  858 void
  859 mtx_validate(struct mtx *m)
  860 {
  861 
  862 /*
  863  * XXX: When kernacc() does not require Giant we can reenable this check
  864  */
  865 #ifdef notyet
  866         /*
  867          * Can't call kernacc() from early init386(), especially when
  868          * initializing Giant mutex, because some stuff in kernacc()
  869          * requires Giant itself.
  870          */
  871         if (!cold)
  872                 if (!kernacc((caddr_t)m, sizeof(m),
  873                     VM_PROT_READ | VM_PROT_WRITE))
  874                         panic("Can't read and write to mutex %p", m);
  875 #endif
  876 }
  877 #endif
  878 
  879 /*
  880  * General init routine used by the MTX_SYSINIT() macro.
  881  */
  882 void
  883 mtx_sysinit(void *arg)
  884 {
  885         struct mtx_args *margs = arg;
  886 
  887         mtx_init((struct mtx *)margs->ma_mtx, margs->ma_desc, NULL,
  888             margs->ma_opts);
  889 }
  890 
  891 /*
  892  * Mutex initialization routine; initialize lock `m' of type contained in
  893  * `opts' with options contained in `opts' and name `name.'  The optional
  894  * lock type `type' is used as a general lock category name for use with
  895  * witness.
  896  */
  897 void
  898 _mtx_init(volatile uintptr_t *c, const char *name, const char *type, int opts)
  899 {
  900         struct mtx *m;
  901         struct lock_class *class;
  902         int flags;
  903 
  904         m = mtxlock2mtx(c);
  905 
  906         MPASS((opts & ~(MTX_SPIN | MTX_QUIET | MTX_RECURSE |
  907                 MTX_NOWITNESS | MTX_DUPOK | MTX_NOPROFILE)) == 0);
  908         ASSERT_ATOMIC_LOAD_PTR(m->mtx_lock,
  909             ("%s: mtx_lock not aligned for %s: %p", __func__, name,
  910             &m->mtx_lock));
  911 
  912 #ifdef MUTEX_DEBUG
  913         /* Diagnostic and error correction */
  914         mtx_validate(m);
  915 #endif
  916 
  917         /* Determine lock class and lock flags. */
  918         if (opts & MTX_SPIN)
  919                 class = &lock_class_mtx_spin;
  920         else
  921                 class = &lock_class_mtx_sleep;
  922         flags = 0;
  923         if (opts & MTX_QUIET)
  924                 flags |= LO_QUIET;
  925         if (opts & MTX_RECURSE)
  926                 flags |= LO_RECURSABLE;
  927         if ((opts & MTX_NOWITNESS) == 0)
  928                 flags |= LO_WITNESS;
  929         if (opts & MTX_DUPOK)
  930                 flags |= LO_DUPOK;
  931         if (opts & MTX_NOPROFILE)
  932                 flags |= LO_NOPROFILE;
  933 
  934         /* Initialize mutex. */
  935         lock_init(&m->lock_object, class, name, type, flags);
  936 
  937         m->mtx_lock = MTX_UNOWNED;
  938         m->mtx_recurse = 0;
  939 }
  940 
  941 /*
  942  * Remove lock `m' from all_mtx queue.  We don't allow MTX_QUIET to be
  943  * passed in as a flag here because if the corresponding mtx_init() was
  944  * called with MTX_QUIET set, then it will already be set in the mutex's
  945  * flags.
  946  */
  947 void
  948 _mtx_destroy(volatile uintptr_t *c)
  949 {
  950         struct mtx *m;
  951 
  952         m = mtxlock2mtx(c);
  953 
  954         if (!mtx_owned(m))
  955                 MPASS(mtx_unowned(m));
  956         else {
  957                 MPASS((m->mtx_lock & (MTX_RECURSED|MTX_CONTESTED)) == 0);
  958 
  959                 /* Perform the non-mtx related part of mtx_unlock_spin(). */
  960                 if (LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin)
  961                         spinlock_exit();
  962                 else
  963                         curthread->td_locks--;
  964 
  965                 lock_profile_release_lock(&m->lock_object);
  966                 /* Tell witness this isn't locked to make it happy. */
  967                 WITNESS_UNLOCK(&m->lock_object, LOP_EXCLUSIVE, __FILE__,
  968                     __LINE__);
  969         }
  970 
  971         m->mtx_lock = MTX_DESTROYED;
  972         lock_destroy(&m->lock_object);
  973 }
  974 
  975 /*
  976  * Intialize the mutex code and system mutexes.  This is called from the MD
  977  * startup code prior to mi_startup().  The per-CPU data space needs to be
  978  * setup before this is called.
  979  */
  980 void
  981 mutex_init(void)
  982 {
  983 
  984         /* Setup turnstiles so that sleep mutexes work. */
  985         init_turnstiles();
  986 
  987         /*
  988          * Initialize mutexes.
  989          */
  990         mtx_init(&Giant, "Giant", NULL, MTX_DEF | MTX_RECURSE);
  991         mtx_init(&blocked_lock, "blocked lock", NULL, MTX_SPIN);
  992         blocked_lock.mtx_lock = 0xdeadc0de;     /* Always blocked. */
  993         mtx_init(&proc0.p_mtx, "process lock", NULL, MTX_DEF | MTX_DUPOK);
  994         mtx_init(&proc0.p_slock, "process slock", NULL, MTX_SPIN | MTX_RECURSE);
  995         mtx_init(&devmtx, "cdev", NULL, MTX_DEF);
  996         mtx_lock(&Giant);
  997 }
  998 
  999 #ifdef DDB
 1000 void
 1001 db_show_mtx(const struct lock_object *lock)
 1002 {
 1003         struct thread *td;
 1004         const struct mtx *m;
 1005 
 1006         m = (const struct mtx *)lock;
 1007 
 1008         db_printf(" flags: {");
 1009         if (LOCK_CLASS(lock) == &lock_class_mtx_spin)
 1010                 db_printf("SPIN");
 1011         else
 1012                 db_printf("DEF");
 1013         if (m->lock_object.lo_flags & LO_RECURSABLE)
 1014                 db_printf(", RECURSE");
 1015         if (m->lock_object.lo_flags & LO_DUPOK)
 1016                 db_printf(", DUPOK");
 1017         db_printf("}\n");
 1018         db_printf(" state: {");
 1019         if (mtx_unowned(m))
 1020                 db_printf("UNOWNED");
 1021         else if (mtx_destroyed(m))
 1022                 db_printf("DESTROYED");
 1023         else {
 1024                 db_printf("OWNED");
 1025                 if (m->mtx_lock & MTX_CONTESTED)
 1026                         db_printf(", CONTESTED");
 1027                 if (m->mtx_lock & MTX_RECURSED)
 1028                         db_printf(", RECURSED");
 1029         }
 1030         db_printf("}\n");
 1031         if (!mtx_unowned(m) && !mtx_destroyed(m)) {
 1032                 td = mtx_owner(m);
 1033                 db_printf(" owner: %p (tid %d, pid %d, \"%s\")\n", td,
 1034                     td->td_tid, td->td_proc->p_pid, td->td_name);
 1035                 if (mtx_recursed(m))
 1036                         db_printf(" recursed: %d\n", m->mtx_recurse);
 1037         }
 1038 }
 1039 #endif

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