The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: 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: stable/10/sys/kern/kern_mutex.c 323870 2017-09-21 19:24:11Z marius $");
   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/smp.h>
   61 #include <sys/sysctl.h>
   62 #include <sys/turnstile.h>
   63 #include <sys/vmmeter.h>
   64 #include <sys/lock_profile.h>
   65 
   66 #include <machine/atomic.h>
   67 #include <machine/bus.h>
   68 #include <machine/cpu.h>
   69 
   70 #include <ddb/ddb.h>
   71 
   72 #include <fs/devfs/devfs_int.h>
   73 
   74 #include <vm/vm.h>
   75 #include <vm/vm_extern.h>
   76 
   77 #if defined(SMP) && !defined(NO_ADAPTIVE_MUTEXES)
   78 #define ADAPTIVE_MUTEXES
   79 #endif
   80 
   81 #ifdef HWPMC_HOOKS
   82 #include <sys/pmckern.h>
   83 PMC_SOFT_DEFINE( , , lock, failed);
   84 #endif
   85 
   86 /*
   87  * Return the mutex address when the lock cookie address is provided.
   88  * This functionality assumes that struct mtx* have a member named mtx_lock.
   89  */
   90 #define mtxlock2mtx(c)  (__containerof(c, struct mtx, mtx_lock))
   91 
   92 /*
   93  * Internal utility macros.
   94  */
   95 #define mtx_unowned(m)  ((m)->mtx_lock == MTX_UNOWNED)
   96 
   97 #define mtx_destroyed(m) ((m)->mtx_lock == MTX_DESTROYED)
   98 
   99 #define mtx_owner(m)    ((struct thread *)((m)->mtx_lock & ~MTX_FLAGMASK))
  100 
  101 static void     assert_mtx(const struct lock_object *lock, int what);
  102 #ifdef DDB
  103 static void     db_show_mtx(const struct lock_object *lock);
  104 #endif
  105 static void     lock_mtx(struct lock_object *lock, uintptr_t how);
  106 static void     lock_spin(struct lock_object *lock, uintptr_t how);
  107 #ifdef KDTRACE_HOOKS
  108 static int      owner_mtx(const struct lock_object *lock,
  109                     struct thread **owner);
  110 #endif
  111 static uintptr_t unlock_mtx(struct lock_object *lock);
  112 static uintptr_t unlock_spin(struct lock_object *lock);
  113 
  114 /*
  115  * Lock classes for sleep and spin mutexes.
  116  */
  117 struct lock_class lock_class_mtx_sleep = {
  118         .lc_name = "sleep mutex",
  119         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
  120         .lc_assert = assert_mtx,
  121 #ifdef DDB
  122         .lc_ddb_show = db_show_mtx,
  123 #endif
  124         .lc_lock = lock_mtx,
  125         .lc_unlock = unlock_mtx,
  126 #ifdef KDTRACE_HOOKS
  127         .lc_owner = owner_mtx,
  128 #endif
  129 };
  130 struct lock_class lock_class_mtx_spin = {
  131         .lc_name = "spin mutex",
  132         .lc_flags = LC_SPINLOCK | LC_RECURSABLE,
  133         .lc_assert = assert_mtx,
  134 #ifdef DDB
  135         .lc_ddb_show = db_show_mtx,
  136 #endif
  137         .lc_lock = lock_spin,
  138         .lc_unlock = unlock_spin,
  139 #ifdef KDTRACE_HOOKS
  140         .lc_owner = owner_mtx,
  141 #endif
  142 };
  143 
  144 #ifdef ADAPTIVE_MUTEXES
  145 static SYSCTL_NODE(_debug, OID_AUTO, mtx, CTLFLAG_RD, NULL, "mtx debugging");
  146 
  147 static struct lock_delay_config mtx_delay = {
  148         .initial        = 1000,
  149         .step           = 500,
  150         .min            = 100,
  151         .max            = 5000,
  152 };
  153 
  154 SYSCTL_INT(_debug_mtx, OID_AUTO, delay_initial, CTLFLAG_RW, &mtx_delay.initial,
  155     0, "");
  156 SYSCTL_INT(_debug_mtx, OID_AUTO, delay_step, CTLFLAG_RW, &mtx_delay.step,
  157     0, "");
  158 SYSCTL_INT(_debug_mtx, OID_AUTO, delay_min, CTLFLAG_RW, &mtx_delay.min,
  159     0, "");
  160 SYSCTL_INT(_debug_mtx, OID_AUTO, delay_max, CTLFLAG_RW, &mtx_delay.max,
  161     0, "");
  162 
  163 static void
  164 mtx_delay_sysinit(void *dummy)
  165 {
  166 
  167         mtx_delay.initial = mp_ncpus * 25;
  168         mtx_delay.step = (mp_ncpus * 25) / 2;
  169         mtx_delay.min = mp_ncpus * 5;
  170         mtx_delay.max = mp_ncpus * 25 * 10;
  171 }
  172 LOCK_DELAY_SYSINIT(mtx_delay_sysinit);
  173 #endif
  174 
  175 /*
  176  * System-wide mutexes
  177  */
  178 struct mtx blocked_lock;
  179 struct mtx Giant;
  180 
  181 void
  182 assert_mtx(const struct lock_object *lock, int what)
  183 {
  184 
  185         mtx_assert((const struct mtx *)lock, what);
  186 }
  187 
  188 void
  189 lock_mtx(struct lock_object *lock, uintptr_t how)
  190 {
  191 
  192         mtx_lock((struct mtx *)lock);
  193 }
  194 
  195 void
  196 lock_spin(struct lock_object *lock, uintptr_t how)
  197 {
  198 
  199         panic("spin locks can only use msleep_spin");
  200 }
  201 
  202 uintptr_t
  203 unlock_mtx(struct lock_object *lock)
  204 {
  205         struct mtx *m;
  206 
  207         m = (struct mtx *)lock;
  208         mtx_assert(m, MA_OWNED | MA_NOTRECURSED);
  209         mtx_unlock(m);
  210         return (0);
  211 }
  212 
  213 uintptr_t
  214 unlock_spin(struct lock_object *lock)
  215 {
  216 
  217         panic("spin locks can only use msleep_spin");
  218 }
  219 
  220 #ifdef KDTRACE_HOOKS
  221 int
  222 owner_mtx(const struct lock_object *lock, struct thread **owner)
  223 {
  224         const struct mtx *m = (const struct mtx *)lock;
  225 
  226         *owner = mtx_owner(m);
  227         return (mtx_unowned(m) == 0);
  228 }
  229 #endif
  230 
  231 /*
  232  * Function versions of the inlined __mtx_* macros.  These are used by
  233  * modules and can also be called from assembly language if needed.
  234  */
  235 void
  236 __mtx_lock_flags(volatile uintptr_t *c, int opts, const char *file, int line)
  237 {
  238         struct mtx *m;
  239 
  240         if (SCHEDULER_STOPPED())
  241                 return;
  242 
  243         m = mtxlock2mtx(c);
  244 
  245         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  246             ("mtx_lock() by idle thread %p on sleep mutex %s @ %s:%d",
  247             curthread, m->lock_object.lo_name, file, line));
  248         KASSERT(m->mtx_lock != MTX_DESTROYED,
  249             ("mtx_lock() of destroyed mutex @ %s:%d", file, line));
  250         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
  251             ("mtx_lock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
  252             file, line));
  253         WITNESS_CHECKORDER(&m->lock_object, (opts & ~MTX_RECURSE) |
  254             LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL);
  255 
  256         __mtx_lock(m, curthread, opts, file, line);
  257         LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
  258             line);
  259         WITNESS_LOCK(&m->lock_object, (opts & ~MTX_RECURSE) | LOP_EXCLUSIVE,
  260             file, line);
  261         curthread->td_locks++;
  262 }
  263 
  264 void
  265 __mtx_unlock_flags(volatile uintptr_t *c, int opts, const char *file, int line)
  266 {
  267         struct mtx *m;
  268 
  269         if (SCHEDULER_STOPPED())
  270                 return;
  271 
  272         m = mtxlock2mtx(c);
  273 
  274         KASSERT(m->mtx_lock != MTX_DESTROYED,
  275             ("mtx_unlock() of destroyed mutex @ %s:%d", file, line));
  276         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
  277             ("mtx_unlock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
  278             file, line));
  279         WITNESS_UNLOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  280         LOCK_LOG_LOCK("UNLOCK", &m->lock_object, opts, m->mtx_recurse, file,
  281             line);
  282         mtx_assert(m, MA_OWNED);
  283 
  284         if (m->mtx_recurse == 0)
  285                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_MTX_UNLOCK_RELEASE, m);
  286         __mtx_unlock(m, curthread, opts, file, line);
  287         curthread->td_locks--;
  288 }
  289 
  290 void
  291 __mtx_lock_spin_flags(volatile uintptr_t *c, int opts, const char *file,
  292     int line)
  293 {
  294         struct mtx *m;
  295 
  296         if (SCHEDULER_STOPPED())
  297                 return;
  298 
  299         m = mtxlock2mtx(c);
  300 
  301         KASSERT(m->mtx_lock != MTX_DESTROYED,
  302             ("mtx_lock_spin() of destroyed mutex @ %s:%d", file, line));
  303         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
  304             ("mtx_lock_spin() of sleep mutex %s @ %s:%d",
  305             m->lock_object.lo_name, file, line));
  306         if (mtx_owned(m))
  307                 KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0 ||
  308                     (opts & MTX_RECURSE) != 0,
  309             ("mtx_lock_spin: recursed on non-recursive mutex %s @ %s:%d\n",
  310                     m->lock_object.lo_name, file, line));
  311         opts &= ~MTX_RECURSE;
  312         WITNESS_CHECKORDER(&m->lock_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE,
  313             file, line, NULL);
  314         __mtx_lock_spin(m, curthread, opts, file, line);
  315         LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
  316             line);
  317         WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  318 }
  319 
  320 int
  321 __mtx_trylock_spin_flags(volatile uintptr_t *c, int opts, const char *file,
  322     int line)
  323 {
  324         struct mtx *m;
  325 
  326         if (SCHEDULER_STOPPED())
  327                 return (1);
  328 
  329         m = mtxlock2mtx(c);
  330 
  331         KASSERT(m->mtx_lock != MTX_DESTROYED,
  332             ("mtx_trylock_spin() of destroyed mutex @ %s:%d", file, line));
  333         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
  334             ("mtx_trylock_spin() of sleep mutex %s @ %s:%d",
  335             m->lock_object.lo_name, file, line));
  336         KASSERT((opts & MTX_RECURSE) == 0,
  337             ("mtx_trylock_spin: unsupp. opt MTX_RECURSE on mutex %s @ %s:%d\n",
  338             m->lock_object.lo_name, file, line));
  339         if (__mtx_trylock_spin(m, curthread, opts, file, line)) {
  340                 LOCK_LOG_TRY("LOCK", &m->lock_object, opts, 1, file, line);
  341                 WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  342                 return (1);
  343         }
  344         LOCK_LOG_TRY("LOCK", &m->lock_object, opts, 0, file, line);
  345         return (0);
  346 }
  347 
  348 void
  349 __mtx_unlock_spin_flags(volatile uintptr_t *c, int opts, const char *file,
  350     int line)
  351 {
  352         struct mtx *m;
  353 
  354         if (SCHEDULER_STOPPED())
  355                 return;
  356 
  357         m = mtxlock2mtx(c);
  358 
  359         KASSERT(m->mtx_lock != MTX_DESTROYED,
  360             ("mtx_unlock_spin() of destroyed mutex @ %s:%d", file, line));
  361         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
  362             ("mtx_unlock_spin() of sleep mutex %s @ %s:%d",
  363             m->lock_object.lo_name, file, line));
  364         WITNESS_UNLOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  365         LOCK_LOG_LOCK("UNLOCK", &m->lock_object, opts, m->mtx_recurse, file,
  366             line);
  367         mtx_assert(m, MA_OWNED);
  368 
  369         __mtx_unlock_spin(m);
  370 }
  371 
  372 /*
  373  * The important part of mtx_trylock{,_flags}()
  374  * Tries to acquire lock `m.'  If this function is called on a mutex that
  375  * is already owned, it will recursively acquire the lock.
  376  */
  377 int
  378 _mtx_trylock_flags_(volatile uintptr_t *c, int opts, const char *file, int line)
  379 {
  380         struct mtx *m;
  381 #ifdef LOCK_PROFILING
  382         uint64_t waittime = 0;
  383         int contested = 0;
  384 #endif
  385         int rval;
  386 
  387         if (SCHEDULER_STOPPED())
  388                 return (1);
  389 
  390         m = mtxlock2mtx(c);
  391 
  392         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  393             ("mtx_trylock() by idle thread %p on sleep mutex %s @ %s:%d",
  394             curthread, m->lock_object.lo_name, file, line));
  395         KASSERT(m->mtx_lock != MTX_DESTROYED,
  396             ("mtx_trylock() of destroyed mutex @ %s:%d", file, line));
  397         KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
  398             ("mtx_trylock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
  399             file, line));
  400 
  401         if (mtx_owned(m) && ((m->lock_object.lo_flags & LO_RECURSABLE) != 0 ||
  402             (opts & MTX_RECURSE) != 0)) {
  403                 m->mtx_recurse++;
  404                 atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
  405                 rval = 1;
  406         } else
  407                 rval = _mtx_obtain_lock(m, (uintptr_t)curthread);
  408         opts &= ~MTX_RECURSE;
  409 
  410         LOCK_LOG_TRY("LOCK", &m->lock_object, opts, rval, file, line);
  411         if (rval) {
  412                 WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE | LOP_TRYLOCK,
  413                     file, line);
  414                 curthread->td_locks++;
  415                 if (m->mtx_recurse == 0)
  416                         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_LOCK_ACQUIRE,
  417                             m, contested, waittime, file, line);
  418 
  419         }
  420 
  421         return (rval);
  422 }
  423 
  424 /*
  425  * __mtx_lock_sleep: the tougher part of acquiring an MTX_DEF lock.
  426  *
  427  * We call this if the lock is either contested (i.e. we need to go to
  428  * sleep waiting for it), or if we need to recurse on it.
  429  */
  430 void
  431 __mtx_lock_sleep(volatile uintptr_t *c, uintptr_t tid, int opts,
  432     const char *file, int line)
  433 {
  434         struct mtx *m;
  435         struct turnstile *ts;
  436         uintptr_t v;
  437 #ifdef ADAPTIVE_MUTEXES
  438         volatile struct thread *owner;
  439 #endif
  440 #ifdef KTR
  441         int cont_logged = 0;
  442 #endif
  443 #ifdef LOCK_PROFILING
  444         int contested = 0;
  445         uint64_t waittime = 0;
  446 #endif
  447 #if defined(ADAPTIVE_MUTEXES) || defined(KDTRACE_HOOKS)
  448         struct lock_delay_arg lda;
  449 #endif
  450 #ifdef KDTRACE_HOOKS
  451         u_int sleep_cnt = 0;
  452         int64_t sleep_time = 0;
  453         int64_t all_time = 0;
  454 #endif
  455 
  456         if (SCHEDULER_STOPPED())
  457                 return;
  458 
  459 #if defined(ADAPTIVE_MUTEXES)
  460         lock_delay_arg_init(&lda, &mtx_delay);
  461 #elif defined(KDTRACE_HOOKS)
  462         lock_delay_arg_init(&lda, NULL);
  463 #endif
  464         m = mtxlock2mtx(c);
  465 
  466         if (mtx_owned(m)) {
  467                 KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0 ||
  468                     (opts & MTX_RECURSE) != 0,
  469             ("_mtx_lock_sleep: recursed on non-recursive mutex %s @ %s:%d\n",
  470                     m->lock_object.lo_name, file, line));
  471                 opts &= ~MTX_RECURSE;
  472                 m->mtx_recurse++;
  473                 atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
  474                 if (LOCK_LOG_TEST(&m->lock_object, opts))
  475                         CTR1(KTR_LOCK, "_mtx_lock_sleep: %p recursing", m);
  476                 return;
  477         }
  478         opts &= ~MTX_RECURSE;
  479 
  480 #ifdef HWPMC_HOOKS
  481         PMC_SOFT_CALL( , , lock, failed);
  482 #endif
  483         lock_profile_obtain_lock_failed(&m->lock_object,
  484                     &contested, &waittime);
  485         if (LOCK_LOG_TEST(&m->lock_object, opts))
  486                 CTR4(KTR_LOCK,
  487                     "_mtx_lock_sleep: %s contested (lock=%p) at %s:%d",
  488                     m->lock_object.lo_name, (void *)m->mtx_lock, file, line);
  489 #ifdef KDTRACE_HOOKS
  490         all_time -= lockstat_nsecs(&m->lock_object);
  491 #endif
  492 
  493         for (;;) {
  494                 if (m->mtx_lock == MTX_UNOWNED && _mtx_obtain_lock(m, tid))
  495                         break;
  496 #ifdef KDTRACE_HOOKS
  497                 lda.spin_cnt++;
  498 #endif
  499 #ifdef ADAPTIVE_MUTEXES
  500                 /*
  501                  * If the owner is running on another CPU, spin until the
  502                  * owner stops running or the state of the lock changes.
  503                  */
  504                 v = m->mtx_lock;
  505                 if (v != MTX_UNOWNED) {
  506                         owner = (struct thread *)(v & ~MTX_FLAGMASK);
  507                         if (TD_IS_RUNNING(owner)) {
  508                                 if (LOCK_LOG_TEST(&m->lock_object, 0))
  509                                         CTR3(KTR_LOCK,
  510                                             "%s: spinning on %p held by %p",
  511                                             __func__, m, owner);
  512                                 KTR_STATE1(KTR_SCHED, "thread",
  513                                     sched_tdname((struct thread *)tid),
  514                                     "spinning", "lockname:\"%s\"",
  515                                     m->lock_object.lo_name);
  516                                 while (mtx_owner(m) == owner &&
  517                                     TD_IS_RUNNING(owner))
  518                                         lock_delay(&lda);
  519                                 KTR_STATE0(KTR_SCHED, "thread",
  520                                     sched_tdname((struct thread *)tid),
  521                                     "running");
  522                                 continue;
  523                         }
  524                 }
  525 #endif
  526 
  527                 ts = turnstile_trywait(&m->lock_object);
  528                 v = m->mtx_lock;
  529 
  530                 /*
  531                  * Check if the lock has been released while spinning for
  532                  * the turnstile chain lock.
  533                  */
  534                 if (v == MTX_UNOWNED) {
  535                         turnstile_cancel(ts);
  536                         continue;
  537                 }
  538 
  539 #ifdef ADAPTIVE_MUTEXES
  540                 /*
  541                  * The current lock owner might have started executing
  542                  * on another CPU (or the lock could have changed
  543                  * owners) while we were waiting on the turnstile
  544                  * chain lock.  If so, drop the turnstile lock and try
  545                  * again.
  546                  */
  547                 owner = (struct thread *)(v & ~MTX_FLAGMASK);
  548                 if (TD_IS_RUNNING(owner)) {
  549                         turnstile_cancel(ts);
  550                         continue;
  551                 }
  552 #endif
  553 
  554                 /*
  555                  * If the mutex isn't already contested and a failure occurs
  556                  * setting the contested bit, the mutex was either released
  557                  * or the state of the MTX_RECURSED bit changed.
  558                  */
  559                 if ((v & MTX_CONTESTED) == 0 &&
  560                     !atomic_cmpset_ptr(&m->mtx_lock, v, v | MTX_CONTESTED)) {
  561                         turnstile_cancel(ts);
  562                         continue;
  563                 }
  564 
  565                 /*
  566                  * We definitely must sleep for this lock.
  567                  */
  568                 mtx_assert(m, MA_NOTOWNED);
  569 
  570 #ifdef KTR
  571                 if (!cont_logged) {
  572                         CTR6(KTR_CONTENTION,
  573                             "contention: %p at %s:%d wants %s, taken by %s:%d",
  574                             (void *)tid, file, line, m->lock_object.lo_name,
  575                             WITNESS_FILE(&m->lock_object),
  576                             WITNESS_LINE(&m->lock_object));
  577                         cont_logged = 1;
  578                 }
  579 #endif
  580 
  581                 /*
  582                  * Block on the turnstile.
  583                  */
  584 #ifdef KDTRACE_HOOKS
  585                 sleep_time -= lockstat_nsecs(&m->lock_object);
  586 #endif
  587                 turnstile_wait(ts, mtx_owner(m), TS_EXCLUSIVE_QUEUE);
  588 #ifdef KDTRACE_HOOKS
  589                 sleep_time += lockstat_nsecs(&m->lock_object);
  590                 sleep_cnt++;
  591 #endif
  592         }
  593 #ifdef KDTRACE_HOOKS
  594         all_time += lockstat_nsecs(&m->lock_object);
  595 #endif
  596 #ifdef KTR
  597         if (cont_logged) {
  598                 CTR4(KTR_CONTENTION,
  599                     "contention end: %s acquired by %p at %s:%d",
  600                     m->lock_object.lo_name, (void *)tid, file, line);
  601         }
  602 #endif
  603         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_LOCK_ACQUIRE, m, contested,
  604             waittime, file, line);
  605 #ifdef KDTRACE_HOOKS
  606         if (sleep_time)
  607                 LOCKSTAT_RECORD1(LS_MTX_LOCK_BLOCK, m, sleep_time);
  608 
  609         /*
  610          * Only record the loops spinning and not sleeping. 
  611          */
  612         if (lda.spin_cnt > sleep_cnt)
  613                 LOCKSTAT_RECORD1(LS_MTX_LOCK_SPIN, m, (all_time - sleep_time));
  614 #endif
  615 }
  616 
  617 static void
  618 _mtx_lock_spin_failed(struct mtx *m)
  619 {
  620         struct thread *td;
  621 
  622         td = mtx_owner(m);
  623 
  624         /* If the mutex is unlocked, try again. */
  625         if (td == NULL)
  626                 return;
  627 
  628         printf( "spin lock %p (%s) held by %p (tid %d) too long\n",
  629             m, m->lock_object.lo_name, td, td->td_tid);
  630 #ifdef WITNESS
  631         witness_display_spinlock(&m->lock_object, td, printf);
  632 #endif
  633         panic("spin lock held too long");
  634 }
  635 
  636 #ifdef SMP
  637 /*
  638  * _mtx_lock_spin_cookie: the tougher part of acquiring an MTX_SPIN lock.
  639  *
  640  * This is only called if we need to actually spin for the lock. Recursion
  641  * is handled inline.
  642  */
  643 void
  644 _mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t tid, int opts,
  645     const char *file, int line)
  646 {
  647         struct mtx *m;
  648         int i = 0;
  649 #ifdef LOCK_PROFILING
  650         int contested = 0;
  651         uint64_t waittime = 0;
  652 #endif
  653 #ifdef KDTRACE_HOOKS
  654         int64_t spin_time = 0;
  655 #endif
  656 
  657         if (SCHEDULER_STOPPED())
  658                 return;
  659 
  660         m = mtxlock2mtx(c);
  661 
  662         if (LOCK_LOG_TEST(&m->lock_object, opts))
  663                 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
  664         KTR_STATE1(KTR_SCHED, "thread", sched_tdname((struct thread *)tid),
  665             "spinning", "lockname:\"%s\"", m->lock_object.lo_name);
  666 
  667 #ifdef HWPMC_HOOKS
  668         PMC_SOFT_CALL( , , lock, failed);
  669 #endif
  670         lock_profile_obtain_lock_failed(&m->lock_object, &contested, &waittime);
  671 #ifdef KDTRACE_HOOKS
  672         spin_time -= lockstat_nsecs(&m->lock_object);
  673 #endif
  674         for (;;) {
  675                 if (m->mtx_lock == MTX_UNOWNED && _mtx_obtain_lock(m, tid))
  676                         break;
  677                 /* Give interrupts a chance while we spin. */
  678                 spinlock_exit();
  679                 while (m->mtx_lock != MTX_UNOWNED) {
  680                         if (i++ < 10000000) {
  681                                 cpu_spinwait();
  682                                 continue;
  683                         }
  684                         if (i < 60000000 || kdb_active || panicstr != NULL)
  685                                 DELAY(1);
  686                         else
  687                                 _mtx_lock_spin_failed(m);
  688                         cpu_spinwait();
  689                 }
  690                 spinlock_enter();
  691         }
  692 #ifdef KDTRACE_HOOKS
  693         spin_time += lockstat_nsecs(&m->lock_object);
  694 #endif
  695 
  696         if (LOCK_LOG_TEST(&m->lock_object, opts))
  697                 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spin done", m);
  698         KTR_STATE0(KTR_SCHED, "thread", sched_tdname((struct thread *)tid),
  699             "running");
  700 
  701         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_SPIN_LOCK_ACQUIRE, m,
  702             contested, waittime, (file), (line));
  703 #ifdef KDTRACE_HOOKS
  704         if (spin_time != 0)
  705                 LOCKSTAT_RECORD1(LS_MTX_SPIN_LOCK_SPIN, m, spin_time);
  706 #endif
  707 }
  708 #endif /* SMP */
  709 
  710 void
  711 thread_lock_flags_(struct thread *td, int opts, const char *file, int line)
  712 {
  713         struct mtx *m;
  714         uintptr_t tid;
  715         int i;
  716 #ifdef LOCK_PROFILING
  717         int contested = 0;
  718         uint64_t waittime = 0;
  719 #endif
  720 #ifdef KDTRACE_HOOKS
  721         int64_t spin_time = 0;
  722 #endif
  723 
  724         i = 0;
  725         tid = (uintptr_t)curthread;
  726 
  727         if (SCHEDULER_STOPPED()) {
  728                 /*
  729                  * Ensure that spinlock sections are balanced even when the
  730                  * scheduler is stopped, since we may otherwise inadvertently
  731                  * re-enable interrupts while dumping core.
  732                  */
  733                 spinlock_enter();
  734                 return;
  735         }
  736 
  737 #ifdef KDTRACE_HOOKS
  738         spin_time -= lockstat_nsecs(&td->td_lock->lock_object);
  739 #endif
  740         for (;;) {
  741 retry:
  742                 spinlock_enter();
  743                 m = td->td_lock;
  744                 KASSERT(m->mtx_lock != MTX_DESTROYED,
  745                     ("thread_lock() of destroyed mutex @ %s:%d", file, line));
  746                 KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
  747                     ("thread_lock() of sleep mutex %s @ %s:%d",
  748                     m->lock_object.lo_name, file, line));
  749                 if (mtx_owned(m))
  750                         KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0,
  751             ("thread_lock: recursed on non-recursive mutex %s @ %s:%d\n",
  752                             m->lock_object.lo_name, file, line));
  753                 WITNESS_CHECKORDER(&m->lock_object,
  754                     opts | LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL);
  755                 for (;;) {
  756                         if (m->mtx_lock == MTX_UNOWNED && _mtx_obtain_lock(m, tid))
  757                                 break;
  758                         if (m->mtx_lock == tid) {
  759                                 m->mtx_recurse++;
  760                                 break;
  761                         }
  762 #ifdef HWPMC_HOOKS
  763                         PMC_SOFT_CALL( , , lock, failed);
  764 #endif
  765                         lock_profile_obtain_lock_failed(&m->lock_object,
  766                             &contested, &waittime);
  767                         /* Give interrupts a chance while we spin. */
  768                         spinlock_exit();
  769                         while (m->mtx_lock != MTX_UNOWNED) {
  770                                 if (i++ < 10000000)
  771                                         cpu_spinwait();
  772                                 else if (i < 60000000 ||
  773                                     kdb_active || panicstr != NULL)
  774                                         DELAY(1);
  775                                 else
  776                                         _mtx_lock_spin_failed(m);
  777                                 cpu_spinwait();
  778                                 if (m != td->td_lock)
  779                                         goto retry;
  780                         }
  781                         spinlock_enter();
  782                 }
  783                 if (m == td->td_lock)
  784                         break;
  785                 __mtx_unlock_spin(m);   /* does spinlock_exit() */
  786         }
  787 #ifdef KDTRACE_HOOKS
  788         spin_time += lockstat_nsecs(&m->lock_object);
  789 #endif
  790         if (m->mtx_recurse == 0)
  791                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_SPIN_LOCK_ACQUIRE,
  792                     m, contested, waittime, (file), (line));
  793         LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
  794             line);
  795         WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
  796         LOCKSTAT_RECORD1(LS_THREAD_LOCK_SPIN, m, spin_time);
  797 }
  798 
  799 struct mtx *
  800 thread_lock_block(struct thread *td)
  801 {
  802         struct mtx *lock;
  803 
  804         THREAD_LOCK_ASSERT(td, MA_OWNED);
  805         lock = td->td_lock;
  806         td->td_lock = &blocked_lock;
  807         mtx_unlock_spin(lock);
  808 
  809         return (lock);
  810 }
  811 
  812 void
  813 thread_lock_unblock(struct thread *td, struct mtx *new)
  814 {
  815         mtx_assert(new, MA_OWNED);
  816         MPASS(td->td_lock == &blocked_lock);
  817         atomic_store_rel_ptr((volatile void *)&td->td_lock, (uintptr_t)new);
  818 }
  819 
  820 void
  821 thread_lock_set(struct thread *td, struct mtx *new)
  822 {
  823         struct mtx *lock;
  824 
  825         mtx_assert(new, MA_OWNED);
  826         THREAD_LOCK_ASSERT(td, MA_OWNED);
  827         lock = td->td_lock;
  828         td->td_lock = new;
  829         mtx_unlock_spin(lock);
  830 }
  831 
  832 /*
  833  * __mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock.
  834  *
  835  * We are only called here if the lock is recursed or contested (i.e. we
  836  * need to wake up a blocked thread).
  837  */
  838 void
  839 __mtx_unlock_sleep(volatile uintptr_t *c, int opts, const char *file, int line)
  840 {
  841         struct mtx *m;
  842         struct turnstile *ts;
  843 
  844         if (SCHEDULER_STOPPED())
  845                 return;
  846 
  847         m = mtxlock2mtx(c);
  848 
  849         if (mtx_recursed(m)) {
  850                 if (--(m->mtx_recurse) == 0)
  851                         atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED);
  852                 if (LOCK_LOG_TEST(&m->lock_object, opts))
  853                         CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p unrecurse", m);
  854                 return;
  855         }
  856 
  857         /*
  858          * We have to lock the chain before the turnstile so this turnstile
  859          * can be removed from the hash list if it is empty.
  860          */
  861         turnstile_chain_lock(&m->lock_object);
  862         ts = turnstile_lookup(&m->lock_object);
  863         if (LOCK_LOG_TEST(&m->lock_object, opts))
  864                 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
  865         MPASS(ts != NULL);
  866         turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE);
  867         _mtx_release_lock_quick(m);
  868 
  869         /*
  870          * This turnstile is now no longer associated with the mutex.  We can
  871          * unlock the chain lock so a new turnstile may take it's place.
  872          */
  873         turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
  874         turnstile_chain_unlock(&m->lock_object);
  875 }
  876 
  877 /*
  878  * All the unlocking of MTX_SPIN locks is done inline.
  879  * See the __mtx_unlock_spin() macro for the details.
  880  */
  881 
  882 /*
  883  * The backing function for the INVARIANTS-enabled mtx_assert()
  884  */
  885 #ifdef INVARIANT_SUPPORT
  886 void
  887 __mtx_assert(const volatile uintptr_t *c, int what, const char *file, int line)
  888 {
  889         const struct mtx *m;
  890 
  891         if (panicstr != NULL || dumping || SCHEDULER_STOPPED())
  892                 return;
  893 
  894         m = mtxlock2mtx(c);
  895 
  896         switch (what) {
  897         case MA_OWNED:
  898         case MA_OWNED | MA_RECURSED:
  899         case MA_OWNED | MA_NOTRECURSED:
  900                 if (!mtx_owned(m))
  901                         panic("mutex %s not owned at %s:%d",
  902                             m->lock_object.lo_name, file, line);
  903                 if (mtx_recursed(m)) {
  904                         if ((what & MA_NOTRECURSED) != 0)
  905                                 panic("mutex %s recursed at %s:%d",
  906                                     m->lock_object.lo_name, file, line);
  907                 } else if ((what & MA_RECURSED) != 0) {
  908                         panic("mutex %s unrecursed at %s:%d",
  909                             m->lock_object.lo_name, file, line);
  910                 }
  911                 break;
  912         case MA_NOTOWNED:
  913                 if (mtx_owned(m))
  914                         panic("mutex %s owned at %s:%d",
  915                             m->lock_object.lo_name, file, line);
  916                 break;
  917         default:
  918                 panic("unknown mtx_assert at %s:%d", file, line);
  919         }
  920 }
  921 #endif
  922 
  923 /*
  924  * The MUTEX_DEBUG-enabled mtx_validate()
  925  *
  926  * Most of these checks have been moved off into the LO_INITIALIZED flag
  927  * maintained by the witness code.
  928  */
  929 #ifdef MUTEX_DEBUG
  930 
  931 void    mtx_validate(struct mtx *);
  932 
  933 void
  934 mtx_validate(struct mtx *m)
  935 {
  936 
  937 /*
  938  * XXX: When kernacc() does not require Giant we can reenable this check
  939  */
  940 #ifdef notyet
  941         /*
  942          * Can't call kernacc() from early init386(), especially when
  943          * initializing Giant mutex, because some stuff in kernacc()
  944          * requires Giant itself.
  945          */
  946         if (!cold)
  947                 if (!kernacc((caddr_t)m, sizeof(m),
  948                     VM_PROT_READ | VM_PROT_WRITE))
  949                         panic("Can't read and write to mutex %p", m);
  950 #endif
  951 }
  952 #endif
  953 
  954 /*
  955  * General init routine used by the MTX_SYSINIT() macro.
  956  */
  957 void
  958 mtx_sysinit(void *arg)
  959 {
  960         struct mtx_args *margs = arg;
  961 
  962         mtx_init((struct mtx *)margs->ma_mtx, margs->ma_desc, NULL,
  963             margs->ma_opts);
  964 }
  965 
  966 /*
  967  * Mutex initialization routine; initialize lock `m' of type contained in
  968  * `opts' with options contained in `opts' and name `name.'  The optional
  969  * lock type `type' is used as a general lock category name for use with
  970  * witness.
  971  */
  972 void
  973 _mtx_init(volatile uintptr_t *c, const char *name, const char *type, int opts)
  974 {
  975         struct mtx *m;
  976         struct lock_class *class;
  977         int flags;
  978 
  979         m = mtxlock2mtx(c);
  980 
  981         MPASS((opts & ~(MTX_SPIN | MTX_QUIET | MTX_RECURSE |
  982             MTX_NOWITNESS | MTX_DUPOK | MTX_NOPROFILE | MTX_NEW)) == 0);
  983         ASSERT_ATOMIC_LOAD_PTR(m->mtx_lock,
  984             ("%s: mtx_lock not aligned for %s: %p", __func__, name,
  985             &m->mtx_lock));
  986 
  987 #ifdef MUTEX_DEBUG
  988         /* Diagnostic and error correction */
  989         mtx_validate(m);
  990 #endif
  991 
  992         /* Determine lock class and lock flags. */
  993         if (opts & MTX_SPIN)
  994                 class = &lock_class_mtx_spin;
  995         else
  996                 class = &lock_class_mtx_sleep;
  997         flags = 0;
  998         if (opts & MTX_QUIET)
  999                 flags |= LO_QUIET;
 1000         if (opts & MTX_RECURSE)
 1001                 flags |= LO_RECURSABLE;
 1002         if ((opts & MTX_NOWITNESS) == 0)
 1003                 flags |= LO_WITNESS;
 1004         if (opts & MTX_DUPOK)
 1005                 flags |= LO_DUPOK;
 1006         if (opts & MTX_NOPROFILE)
 1007                 flags |= LO_NOPROFILE;
 1008         if (opts & MTX_NEW)
 1009                 flags |= LO_NEW;
 1010 
 1011         /* Initialize mutex. */
 1012         lock_init(&m->lock_object, class, name, type, flags);
 1013 
 1014         m->mtx_lock = MTX_UNOWNED;
 1015         m->mtx_recurse = 0;
 1016 }
 1017 
 1018 /*
 1019  * Remove lock `m' from all_mtx queue.  We don't allow MTX_QUIET to be
 1020  * passed in as a flag here because if the corresponding mtx_init() was
 1021  * called with MTX_QUIET set, then it will already be set in the mutex's
 1022  * flags.
 1023  */
 1024 void
 1025 _mtx_destroy(volatile uintptr_t *c)
 1026 {
 1027         struct mtx *m;
 1028 
 1029         m = mtxlock2mtx(c);
 1030 
 1031         if (!mtx_owned(m))
 1032                 MPASS(mtx_unowned(m));
 1033         else {
 1034                 MPASS((m->mtx_lock & (MTX_RECURSED|MTX_CONTESTED)) == 0);
 1035 
 1036                 /* Perform the non-mtx related part of mtx_unlock_spin(). */
 1037                 if (LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin)
 1038                         spinlock_exit();
 1039                 else
 1040                         curthread->td_locks--;
 1041 
 1042                 lock_profile_release_lock(&m->lock_object);
 1043                 /* Tell witness this isn't locked to make it happy. */
 1044                 WITNESS_UNLOCK(&m->lock_object, LOP_EXCLUSIVE, __FILE__,
 1045                     __LINE__);
 1046         }
 1047 
 1048         m->mtx_lock = MTX_DESTROYED;
 1049         lock_destroy(&m->lock_object);
 1050 }
 1051 
 1052 /*
 1053  * Intialize the mutex code and system mutexes.  This is called from the MD
 1054  * startup code prior to mi_startup().  The per-CPU data space needs to be
 1055  * setup before this is called.
 1056  */
 1057 void
 1058 mutex_init(void)
 1059 {
 1060 
 1061         /* Setup turnstiles so that sleep mutexes work. */
 1062         init_turnstiles();
 1063 
 1064         /*
 1065          * Initialize mutexes.
 1066          */
 1067         mtx_init(&Giant, "Giant", NULL, MTX_DEF | MTX_RECURSE);
 1068         mtx_init(&blocked_lock, "blocked lock", NULL, MTX_SPIN);
 1069         blocked_lock.mtx_lock = 0xdeadc0de;     /* Always blocked. */
 1070         mtx_init(&proc0.p_mtx, "process lock", NULL, MTX_DEF | MTX_DUPOK);
 1071         mtx_init(&proc0.p_slock, "process slock", NULL, MTX_SPIN | MTX_RECURSE);
 1072         mtx_init(&devmtx, "cdev", NULL, MTX_DEF);
 1073         mtx_lock(&Giant);
 1074 }
 1075 
 1076 #ifdef DDB
 1077 void
 1078 db_show_mtx(const struct lock_object *lock)
 1079 {
 1080         struct thread *td;
 1081         const struct mtx *m;
 1082 
 1083         m = (const struct mtx *)lock;
 1084 
 1085         db_printf(" flags: {");
 1086         if (LOCK_CLASS(lock) == &lock_class_mtx_spin)
 1087                 db_printf("SPIN");
 1088         else
 1089                 db_printf("DEF");
 1090         if (m->lock_object.lo_flags & LO_RECURSABLE)
 1091                 db_printf(", RECURSE");
 1092         if (m->lock_object.lo_flags & LO_DUPOK)
 1093                 db_printf(", DUPOK");
 1094         db_printf("}\n");
 1095         db_printf(" state: {");
 1096         if (mtx_unowned(m))
 1097                 db_printf("UNOWNED");
 1098         else if (mtx_destroyed(m))
 1099                 db_printf("DESTROYED");
 1100         else {
 1101                 db_printf("OWNED");
 1102                 if (m->mtx_lock & MTX_CONTESTED)
 1103                         db_printf(", CONTESTED");
 1104                 if (m->mtx_lock & MTX_RECURSED)
 1105                         db_printf(", RECURSED");
 1106         }
 1107         db_printf("}\n");
 1108         if (!mtx_unowned(m) && !mtx_destroyed(m)) {
 1109                 td = mtx_owner(m);
 1110                 db_printf(" owner: %p (tid %d, pid %d, \"%s\")\n", td,
 1111                     td->td_tid, td->td_proc->p_pid, td->td_name);
 1112                 if (mtx_recursed(m))
 1113                         db_printf(" recursed: %d\n", m->mtx_recurse);
 1114         }
 1115 }
 1116 #endif

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