The Design and Implementation of the FreeBSD Operating System, Second Edition
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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  * $FreeBSD: src/sys/kern/kern_mutex.c,v 1.116 2002/10/25 08:40:20 phk Exp $
   31  */
   32 
   33 /*
   34  * Machine independent bits of mutex implementation.
   35  */
   36 
   37 #include "opt_adaptive_mutexes.h"
   38 #include "opt_ddb.h"
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/bus.h>
   43 #include <sys/kernel.h>
   44 #include <sys/ktr.h>
   45 #include <sys/lock.h>
   46 #include <sys/malloc.h>
   47 #include <sys/mutex.h>
   48 #include <sys/proc.h>
   49 #include <sys/resourcevar.h>
   50 #include <sys/sched.h>
   51 #include <sys/sbuf.h>
   52 #include <sys/stdint.h>
   53 #include <sys/sysctl.h>
   54 #include <sys/vmmeter.h>
   55 
   56 #include <machine/atomic.h>
   57 #include <machine/bus.h>
   58 #include <machine/clock.h>
   59 #include <machine/cpu.h>
   60 
   61 #include <ddb/ddb.h>
   62 
   63 #include <vm/vm.h>
   64 #include <vm/vm_extern.h>
   65 
   66 /*
   67  * Internal utility macros.
   68  */
   69 #define mtx_unowned(m)  ((m)->mtx_lock == MTX_UNOWNED)
   70 
   71 #define mtx_owner(m)    (mtx_unowned((m)) ? NULL \
   72         : (struct thread *)((m)->mtx_lock & MTX_FLAGMASK))
   73 
   74 /* XXXKSE This test will change. */
   75 #define thread_running(td)                                              \
   76         ((td)->td_kse != NULL && (td)->td_kse->ke_oncpu != NOCPU)
   77 
   78 /*
   79  * Lock classes for sleep and spin mutexes.
   80  */
   81 struct lock_class lock_class_mtx_sleep = {
   82         "sleep mutex",
   83         LC_SLEEPLOCK | LC_RECURSABLE
   84 };
   85 struct lock_class lock_class_mtx_spin = {
   86         "spin mutex",
   87         LC_SPINLOCK | LC_RECURSABLE
   88 };
   89 
   90 /*
   91  * System-wide mutexes
   92  */
   93 struct mtx sched_lock;
   94 struct mtx Giant;
   95 
   96 /*
   97  * Prototypes for non-exported routines.
   98  */
   99 static void     propagate_priority(struct thread *);
  100 
  101 static void
  102 propagate_priority(struct thread *td)
  103 {
  104         int pri = td->td_priority;
  105         struct mtx *m = td->td_blocked;
  106 
  107         mtx_assert(&sched_lock, MA_OWNED);
  108         for (;;) {
  109                 struct thread *td1;
  110 
  111                 td = mtx_owner(m);
  112 
  113                 if (td == NULL) {
  114                         /*
  115                          * This really isn't quite right. Really
  116                          * ought to bump priority of thread that
  117                          * next acquires the mutex.
  118                          */
  119                         MPASS(m->mtx_lock == MTX_CONTESTED);
  120                         return;
  121                 }
  122 
  123                 MPASS(td->td_proc != NULL);
  124                 MPASS(td->td_proc->p_magic == P_MAGIC);
  125                 KASSERT(!TD_IS_SLEEPING(td), ("sleeping thread owns a mutex"));
  126                 if (td->td_priority <= pri) /* lower is higher priority */
  127                         return;
  128 
  129 
  130                 /*
  131                  * If lock holder is actually running, just bump priority.
  132                  */
  133                 if (TD_IS_RUNNING(td)) {
  134                         td->td_priority = pri;
  135                         return;
  136                 }
  137 
  138 #ifndef SMP
  139                 /*
  140                  * For UP, we check to see if td is curthread (this shouldn't
  141                  * ever happen however as it would mean we are in a deadlock.)
  142                  */
  143                 KASSERT(td != curthread, ("Deadlock detected"));
  144 #endif
  145 
  146                 /*
  147                  * If on run queue move to new run queue, and quit.
  148                  * XXXKSE this gets a lot more complicated under threads
  149                  * but try anyhow.
  150                  */
  151                 if (TD_ON_RUNQ(td)) {
  152                         MPASS(td->td_blocked == NULL);
  153                         sched_prio(td, pri);
  154                         return;
  155                 }
  156                 /*
  157                  * Adjust for any other cases.
  158                  */
  159                 td->td_priority = pri;
  160 
  161                 /*
  162                  * If we aren't blocked on a mutex, we should be.
  163                  */
  164                 KASSERT(TD_ON_LOCK(td), (
  165                     "process %d(%s):%d holds %s but isn't blocked on a mutex\n",
  166                     td->td_proc->p_pid, td->td_proc->p_comm, td->td_state,
  167                     m->mtx_object.lo_name));
  168 
  169                 /*
  170                  * Pick up the mutex that td is blocked on.
  171                  */
  172                 m = td->td_blocked;
  173                 MPASS(m != NULL);
  174 
  175                 /*
  176                  * Check if the thread needs to be moved up on
  177                  * the blocked chain
  178                  */
  179                 if (td == TAILQ_FIRST(&m->mtx_blocked)) {
  180                         continue;
  181                 }
  182 
  183                 td1 = TAILQ_PREV(td, threadqueue, td_lockq);
  184                 if (td1->td_priority <= pri) {
  185                         continue;
  186                 }
  187 
  188                 /*
  189                  * Remove thread from blocked chain and determine where
  190                  * it should be moved up to.  Since we know that td1 has
  191                  * a lower priority than td, we know that at least one
  192                  * thread in the chain has a lower priority and that
  193                  * td1 will thus not be NULL after the loop.
  194                  */
  195                 TAILQ_REMOVE(&m->mtx_blocked, td, td_lockq);
  196                 TAILQ_FOREACH(td1, &m->mtx_blocked, td_lockq) {
  197                         MPASS(td1->td_proc->p_magic == P_MAGIC);
  198                         if (td1->td_priority > pri)
  199                                 break;
  200                 }
  201 
  202                 MPASS(td1 != NULL);
  203                 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
  204                 CTR4(KTR_LOCK,
  205                     "propagate_priority: p %p moved before %p on [%p] %s",
  206                     td, td1, m, m->mtx_object.lo_name);
  207         }
  208 }
  209 
  210 #ifdef MUTEX_PROFILING
  211 SYSCTL_NODE(_debug, OID_AUTO, mutex, CTLFLAG_RD, NULL, "mutex debugging");
  212 SYSCTL_NODE(_debug_mutex, OID_AUTO, prof, CTLFLAG_RD, NULL, "mutex profiling");
  213 static int mutex_prof_enable = 0;
  214 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, enable, CTLFLAG_RW,
  215     &mutex_prof_enable, 0, "Enable tracing of mutex holdtime");
  216 
  217 struct mutex_prof {
  218         const char      *name;
  219         const char      *file;
  220         int             line;
  221         struct {
  222                 uintmax_t       max;
  223                 uintmax_t       tot;
  224                 uintmax_t       cur;
  225         } cnt;
  226         struct mutex_prof *next;
  227 };
  228 
  229 /*
  230  * mprof_buf is a static pool of profiling records to avoid possible
  231  * reentrance of the memory allocation functions.
  232  *
  233  * Note: NUM_MPROF_BUFFERS must be smaller than MPROF_HASH_SIZE.
  234  */
  235 #define NUM_MPROF_BUFFERS       1000
  236 static struct mutex_prof mprof_buf[NUM_MPROF_BUFFERS];
  237 static int first_free_mprof_buf;
  238 #define MPROF_HASH_SIZE         1009
  239 static struct mutex_prof *mprof_hash[MPROF_HASH_SIZE];
  240 
  241 static int mutex_prof_acquisitions;
  242 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, acquisitions, CTLFLAG_RD,
  243     &mutex_prof_acquisitions, 0, "Number of mutex acquistions recorded");
  244 static int mutex_prof_records;
  245 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, records, CTLFLAG_RD,
  246     &mutex_prof_records, 0, "Number of profiling records");
  247 static int mutex_prof_maxrecords = NUM_MPROF_BUFFERS;
  248 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, maxrecords, CTLFLAG_RD,
  249     &mutex_prof_maxrecords, 0, "Maximum number of profiling records");
  250 static int mutex_prof_rejected;
  251 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, rejected, CTLFLAG_RD,
  252     &mutex_prof_rejected, 0, "Number of rejected profiling records");
  253 static int mutex_prof_hashsize = MPROF_HASH_SIZE;
  254 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, hashsize, CTLFLAG_RD,
  255     &mutex_prof_hashsize, 0, "Hash size");
  256 static int mutex_prof_collisions = 0;
  257 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, collisions, CTLFLAG_RD,
  258     &mutex_prof_collisions, 0, "Number of hash collisions");
  259 
  260 /*
  261  * mprof_mtx protects the profiling buffers and the hash.
  262  */
  263 static struct mtx mprof_mtx;
  264 MTX_SYSINIT(mprof, &mprof_mtx, "mutex profiling lock", MTX_SPIN | MTX_QUIET);
  265 
  266 static u_int64_t
  267 nanoseconds(void)
  268 {
  269         struct timespec tv;
  270 
  271         nanotime(&tv);
  272         return (tv.tv_sec * (u_int64_t)1000000000 + tv.tv_nsec);
  273 }
  274 
  275 static int
  276 dump_mutex_prof_stats(SYSCTL_HANDLER_ARGS)
  277 {
  278         struct sbuf *sb;
  279         int error, i;
  280 
  281         if (first_free_mprof_buf == 0)
  282                 return (SYSCTL_OUT(req, "No locking recorded",
  283                     sizeof("No locking recorded")));
  284 
  285         sb = sbuf_new(NULL, NULL, 1024, SBUF_AUTOEXTEND);
  286         sbuf_printf(sb, "%6s %12s %11s %5s %s\n",
  287             "max", "total", "count", "avg", "name");
  288         /*
  289          * XXX this spinlock seems to be by far the largest perpetrator
  290          * of spinlock latency (1.6 msec on an Athlon1600 was recorded
  291          * even before I pessimized it further by moving the average
  292          * computation here).
  293          */
  294         mtx_lock_spin(&mprof_mtx);
  295         for (i = 0; i < first_free_mprof_buf; ++i)
  296                 sbuf_printf(sb, "%6ju %12ju %11ju %5ju %s:%d (%s)\n",
  297                     mprof_buf[i].cnt.max / 1000,
  298                     mprof_buf[i].cnt.tot / 1000,
  299                     mprof_buf[i].cnt.cur,
  300                     mprof_buf[i].cnt.cur == 0 ? (uintmax_t)0 :
  301                         mprof_buf[i].cnt.tot / (mprof_buf[i].cnt.cur * 1000),
  302                     mprof_buf[i].file, mprof_buf[i].line, mprof_buf[i].name);
  303         mtx_unlock_spin(&mprof_mtx);
  304         sbuf_finish(sb);
  305         error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1);
  306         sbuf_delete(sb);
  307         return (error);
  308 }
  309 SYSCTL_PROC(_debug_mutex_prof, OID_AUTO, stats, CTLTYPE_STRING | CTLFLAG_RD,
  310     NULL, 0, dump_mutex_prof_stats, "A", "Mutex profiling statistics");
  311 #endif
  312 
  313 /*
  314  * Function versions of the inlined __mtx_* macros.  These are used by
  315  * modules and can also be called from assembly language if needed.
  316  */
  317 void
  318 _mtx_lock_flags(struct mtx *m, int opts, const char *file, int line)
  319 {
  320 
  321         MPASS(curthread != NULL);
  322         KASSERT(m->mtx_object.lo_class == &lock_class_mtx_sleep,
  323             ("mtx_lock() of spin mutex %s @ %s:%d", m->mtx_object.lo_name,
  324             file, line));
  325         _get_sleep_lock(m, curthread, opts, file, line);
  326         LOCK_LOG_LOCK("LOCK", &m->mtx_object, opts, m->mtx_recurse, file,
  327             line);
  328         WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
  329 #ifdef MUTEX_PROFILING
  330         /* don't reset the timer when/if recursing */
  331         if (m->mtx_acqtime == 0) {
  332                 m->mtx_filename = file;
  333                 m->mtx_lineno = line;
  334                 m->mtx_acqtime = mutex_prof_enable ? nanoseconds() : 0;
  335                 ++mutex_prof_acquisitions;
  336         }
  337 #endif
  338 }
  339 
  340 void
  341 _mtx_unlock_flags(struct mtx *m, int opts, const char *file, int line)
  342 {
  343 
  344         MPASS(curthread != NULL);
  345         KASSERT(m->mtx_object.lo_class == &lock_class_mtx_sleep,
  346             ("mtx_unlock() of spin mutex %s @ %s:%d", m->mtx_object.lo_name,
  347             file, line));
  348         WITNESS_UNLOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
  349         LOCK_LOG_LOCK("UNLOCK", &m->mtx_object, opts, m->mtx_recurse, file,
  350             line);
  351         mtx_assert(m, MA_OWNED);
  352 #ifdef MUTEX_PROFILING
  353         if (m->mtx_acqtime != 0) {
  354                 static const char *unknown = "(unknown)";
  355                 struct mutex_prof *mpp;
  356                 u_int64_t acqtime, now;
  357                 const char *p, *q;
  358                 volatile u_int hash;
  359 
  360                 now = nanoseconds();
  361                 acqtime = m->mtx_acqtime;
  362                 m->mtx_acqtime = 0;
  363                 if (now <= acqtime)
  364                         goto out;
  365                 for (p = m->mtx_filename; strncmp(p, "../", 3) == 0; p += 3)
  366                         /* nothing */ ;
  367                 if (p == NULL || *p == '\0')
  368                         p = unknown;
  369                 for (hash = m->mtx_lineno, q = p; *q != '\0'; ++q)
  370                         hash = (hash * 2 + *q) % MPROF_HASH_SIZE;
  371                 mtx_lock_spin(&mprof_mtx);
  372                 for (mpp = mprof_hash[hash]; mpp != NULL; mpp = mpp->next)
  373                         if (mpp->line == m->mtx_lineno &&
  374                             strcmp(mpp->file, p) == 0)
  375                                 break;
  376                 if (mpp == NULL) {
  377                         /* Just exit if we cannot get a trace buffer */
  378                         if (first_free_mprof_buf >= NUM_MPROF_BUFFERS) {
  379                                 ++mutex_prof_rejected;
  380                                 goto unlock;
  381                         }
  382                         mpp = &mprof_buf[first_free_mprof_buf++];
  383                         mpp->name = mtx_name(m);
  384                         mpp->file = p;
  385                         mpp->line = m->mtx_lineno;
  386                         mpp->next = mprof_hash[hash];
  387                         if (mprof_hash[hash] != NULL)
  388                                 ++mutex_prof_collisions;
  389                         mprof_hash[hash] = mpp;
  390                         ++mutex_prof_records;
  391                 }
  392                 /*
  393                  * Record if the mutex has been held longer now than ever
  394                  * before.
  395                  */
  396                 if (now - acqtime > mpp->cnt.max)
  397                         mpp->cnt.max = now - acqtime;
  398                 mpp->cnt.tot += now - acqtime;
  399                 mpp->cnt.cur++;
  400 unlock:
  401                 mtx_unlock_spin(&mprof_mtx);
  402         }
  403 out:
  404 #endif
  405         _rel_sleep_lock(m, curthread, opts, file, line);
  406 }
  407 
  408 void
  409 _mtx_lock_spin_flags(struct mtx *m, int opts, const char *file, int line)
  410 {
  411 
  412         MPASS(curthread != NULL);
  413         KASSERT(m->mtx_object.lo_class == &lock_class_mtx_spin,
  414             ("mtx_lock_spin() of sleep mutex %s @ %s:%d",
  415             m->mtx_object.lo_name, file, line));
  416 #if defined(SMP) || LOCK_DEBUG > 0 || 1
  417         _get_spin_lock(m, curthread, opts, file, line);
  418 #else
  419         critical_enter();
  420 #endif
  421         LOCK_LOG_LOCK("LOCK", &m->mtx_object, opts, m->mtx_recurse, file,
  422             line);
  423         WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
  424 }
  425 
  426 void
  427 _mtx_unlock_spin_flags(struct mtx *m, int opts, const char *file, int line)
  428 {
  429 
  430         MPASS(curthread != NULL);
  431         KASSERT(m->mtx_object.lo_class == &lock_class_mtx_spin,
  432             ("mtx_unlock_spin() of sleep mutex %s @ %s:%d",
  433             m->mtx_object.lo_name, file, line));
  434         WITNESS_UNLOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
  435         LOCK_LOG_LOCK("UNLOCK", &m->mtx_object, opts, m->mtx_recurse, file,
  436             line);
  437         mtx_assert(m, MA_OWNED);
  438 #if defined(SMP) || LOCK_DEBUG > 0 || 1
  439         _rel_spin_lock(m);
  440 #else
  441         critical_exit();
  442 #endif
  443 }
  444 
  445 /*
  446  * The important part of mtx_trylock{,_flags}()
  447  * Tries to acquire lock `m.' We do NOT handle recursion here; we assume that
  448  * if we're called, it's because we know we don't already own this lock.
  449  */
  450 int
  451 _mtx_trylock(struct mtx *m, int opts, const char *file, int line)
  452 {
  453         int rval;
  454 
  455         MPASS(curthread != NULL);
  456 
  457         rval = _obtain_lock(m, curthread);
  458 
  459         LOCK_LOG_TRY("LOCK", &m->mtx_object, opts, rval, file, line);
  460         if (rval) {
  461                 /*
  462                  * We do not handle recursion in _mtx_trylock; see the
  463                  * note at the top of the routine.
  464                  */
  465                 KASSERT(!mtx_recursed(m),
  466                     ("mtx_trylock() called on a recursed mutex"));
  467                 WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE | LOP_TRYLOCK,
  468                     file, line);
  469         }
  470 
  471         return (rval);
  472 }
  473 
  474 /*
  475  * _mtx_lock_sleep: the tougher part of acquiring an MTX_DEF lock.
  476  *
  477  * We call this if the lock is either contested (i.e. we need to go to
  478  * sleep waiting for it), or if we need to recurse on it.
  479  */
  480 void
  481 _mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
  482 {
  483         struct thread *td = curthread;
  484 #if defined(SMP) && defined(ADAPTIVE_MUTEXES)
  485         struct thread *owner;
  486 #endif
  487 #ifdef KTR
  488         int cont_logged = 0;
  489 #endif
  490 
  491         if ((m->mtx_lock & MTX_FLAGMASK) == (uintptr_t)td) {
  492                 m->mtx_recurse++;
  493                 atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
  494                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  495                         CTR1(KTR_LOCK, "_mtx_lock_sleep: %p recursing", m);
  496                 return;
  497         }
  498 
  499         if (LOCK_LOG_TEST(&m->mtx_object, opts))
  500                 CTR4(KTR_LOCK,
  501                     "_mtx_lock_sleep: %s contested (lock=%p) at %s:%d",
  502                     m->mtx_object.lo_name, (void *)m->mtx_lock, file, line);
  503 
  504         while (!_obtain_lock(m, td)) {
  505                 uintptr_t v;
  506                 struct thread *td1;
  507 
  508                 mtx_lock_spin(&sched_lock);
  509                 /*
  510                  * Check if the lock has been released while spinning for
  511                  * the sched_lock.
  512                  */
  513                 if ((v = m->mtx_lock) == MTX_UNOWNED) {
  514                         mtx_unlock_spin(&sched_lock);
  515 #ifdef __i386__
  516                         ia32_pause();
  517 #endif
  518                         continue;
  519                 }
  520 
  521                 /*
  522                  * The mutex was marked contested on release. This means that
  523                  * there are threads blocked on it.
  524                  */
  525                 if (v == MTX_CONTESTED) {
  526                         td1 = TAILQ_FIRST(&m->mtx_blocked);
  527                         MPASS(td1 != NULL);
  528                         m->mtx_lock = (uintptr_t)td | MTX_CONTESTED;
  529 
  530                         if (td1->td_priority < td->td_priority)
  531                                 td->td_priority = td1->td_priority;
  532                         mtx_unlock_spin(&sched_lock);
  533                         return;
  534                 }
  535 
  536                 /*
  537                  * If the mutex isn't already contested and a failure occurs
  538                  * setting the contested bit, the mutex was either released
  539                  * or the state of the MTX_RECURSED bit changed.
  540                  */
  541                 if ((v & MTX_CONTESTED) == 0 &&
  542                     !atomic_cmpset_ptr(&m->mtx_lock, (void *)v,
  543                         (void *)(v | MTX_CONTESTED))) {
  544                         mtx_unlock_spin(&sched_lock);
  545 #ifdef __i386__
  546                         ia32_pause();
  547 #endif
  548                         continue;
  549                 }
  550 
  551 #if defined(SMP) && defined(ADAPTIVE_MUTEXES)
  552                 /*
  553                  * If the current owner of the lock is executing on another
  554                  * CPU, spin instead of blocking.
  555                  */
  556                 owner = (struct thread *)(v & MTX_FLAGMASK);
  557                 if (m != &Giant && thread_running(owner)) {
  558                         mtx_unlock_spin(&sched_lock);
  559                         while (mtx_owner(m) == owner && thread_running(owner)) {
  560 #ifdef __i386__
  561                                 ia32_pause();
  562 #endif
  563                         }
  564                         continue;
  565                 }
  566 #endif  /* SMP && ADAPTIVE_MUTEXES */
  567 
  568                 /*
  569                  * We definitely must sleep for this lock.
  570                  */
  571                 mtx_assert(m, MA_NOTOWNED);
  572 
  573 #ifdef notyet
  574                 /*
  575                  * If we're borrowing an interrupted thread's VM context, we
  576                  * must clean up before going to sleep.
  577                  */
  578                 if (td->td_ithd != NULL) {
  579                         struct ithd *it = td->td_ithd;
  580 
  581                         if (it->it_interrupted) {
  582                                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  583                                         CTR2(KTR_LOCK,
  584                                     "_mtx_lock_sleep: %p interrupted %p",
  585                                             it, it->it_interrupted);
  586                                 intr_thd_fixup(it);
  587                         }
  588                 }
  589 #endif
  590 
  591                 /*
  592                  * Put us on the list of threads blocked on this mutex.
  593                  */
  594                 if (TAILQ_EMPTY(&m->mtx_blocked)) {
  595                         td1 = mtx_owner(m);
  596                         LIST_INSERT_HEAD(&td1->td_contested, m, mtx_contested);
  597                         TAILQ_INSERT_TAIL(&m->mtx_blocked, td, td_lockq);
  598                 } else {
  599                         TAILQ_FOREACH(td1, &m->mtx_blocked, td_lockq)
  600                                 if (td1->td_priority > td->td_priority)
  601                                         break;
  602                         if (td1)
  603                                 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
  604                         else
  605                                 TAILQ_INSERT_TAIL(&m->mtx_blocked, td, td_lockq);
  606                 }
  607 #ifdef KTR
  608                 if (!cont_logged) {
  609                         CTR6(KTR_CONTENTION,
  610                             "contention: %p at %s:%d wants %s, taken by %s:%d",
  611                             td, file, line, m->mtx_object.lo_name,
  612                             WITNESS_FILE(&m->mtx_object),
  613                             WITNESS_LINE(&m->mtx_object));
  614                         cont_logged = 1;
  615                 }
  616 #endif
  617 
  618                 /*
  619                  * Save who we're blocked on.
  620                  */
  621                 td->td_blocked = m;
  622                 td->td_lockname = m->mtx_object.lo_name;
  623                 TD_SET_LOCK(td);
  624                 propagate_priority(td);
  625 
  626                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  627                         CTR3(KTR_LOCK,
  628                             "_mtx_lock_sleep: p %p blocked on [%p] %s", td, m,
  629                             m->mtx_object.lo_name);
  630 
  631                 td->td_proc->p_stats->p_ru.ru_nvcsw++;
  632                 mi_switch();
  633 
  634                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  635                         CTR3(KTR_LOCK,
  636                           "_mtx_lock_sleep: p %p free from blocked on [%p] %s",
  637                           td, m, m->mtx_object.lo_name);
  638 
  639                 mtx_unlock_spin(&sched_lock);
  640         }
  641 
  642 #ifdef KTR
  643         if (cont_logged) {
  644                 CTR4(KTR_CONTENTION,
  645                     "contention end: %s acquired by %p at %s:%d",
  646                     m->mtx_object.lo_name, td, file, line);
  647         }
  648 #endif
  649         return;
  650 }
  651 
  652 /*
  653  * _mtx_lock_spin: the tougher part of acquiring an MTX_SPIN lock.
  654  *
  655  * This is only called if we need to actually spin for the lock. Recursion
  656  * is handled inline.
  657  */
  658 void
  659 _mtx_lock_spin(struct mtx *m, int opts, const char *file, int line)
  660 {
  661         int i = 0;
  662 
  663         if (LOCK_LOG_TEST(&m->mtx_object, opts))
  664                 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
  665 
  666         for (;;) {
  667                 if (_obtain_lock(m, curthread))
  668                         break;
  669 
  670                 /* Give interrupts a chance while we spin. */
  671                 critical_exit();
  672                 while (m->mtx_lock != MTX_UNOWNED) {
  673                         if (i++ < 10000000) {
  674 #ifdef __i386__
  675                                 ia32_pause();
  676 #endif
  677                                 continue;
  678                         }
  679                         if (i < 60000000)
  680                                 DELAY(1);
  681 #ifdef DDB
  682                         else if (!db_active)
  683 #else
  684                         else
  685 #endif
  686                                 panic("spin lock %s held by %p for > 5 seconds",
  687                                     m->mtx_object.lo_name, (void *)m->mtx_lock);
  688 #ifdef __i386__
  689                         ia32_pause();
  690 #endif
  691                 }
  692                 critical_enter();
  693         }
  694 
  695         if (LOCK_LOG_TEST(&m->mtx_object, opts))
  696                 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spin done", m);
  697 
  698         return;
  699 }
  700 
  701 /*
  702  * _mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock.
  703  *
  704  * We are only called here if the lock is recursed or contested (i.e. we
  705  * need to wake up a blocked thread).
  706  */
  707 void
  708 _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
  709 {
  710         struct thread *td, *td1;
  711         struct mtx *m1;
  712         int pri;
  713 
  714         td = curthread;
  715 
  716         if (mtx_recursed(m)) {
  717                 if (--(m->mtx_recurse) == 0)
  718                         atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED);
  719                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  720                         CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p unrecurse", m);
  721                 return;
  722         }
  723 
  724         mtx_lock_spin(&sched_lock);
  725         if (LOCK_LOG_TEST(&m->mtx_object, opts))
  726                 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
  727 
  728         td1 = TAILQ_FIRST(&m->mtx_blocked);
  729 #if defined(SMP) && defined(ADAPTIVE_MUTEXES)
  730         if (td1 == NULL) {
  731                 _release_lock_quick(m);
  732                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  733                         CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p no sleepers", m);
  734                 mtx_unlock_spin(&sched_lock);
  735                 return;
  736         }
  737 #endif
  738         MPASS(td->td_proc->p_magic == P_MAGIC);
  739         MPASS(td1->td_proc->p_magic == P_MAGIC);
  740 
  741         TAILQ_REMOVE(&m->mtx_blocked, td1, td_lockq);
  742 
  743         if (TAILQ_EMPTY(&m->mtx_blocked)) {
  744                 LIST_REMOVE(m, mtx_contested);
  745                 _release_lock_quick(m);
  746                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  747                         CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p not held", m);
  748         } else
  749                 atomic_store_rel_ptr(&m->mtx_lock, (void *)MTX_CONTESTED);
  750 
  751         pri = PRI_MAX;
  752         LIST_FOREACH(m1, &td->td_contested, mtx_contested) {
  753                 int cp = TAILQ_FIRST(&m1->mtx_blocked)->td_priority;
  754                 if (cp < pri)
  755                         pri = cp;
  756         }
  757 
  758         if (pri > td->td_base_pri)
  759                 pri = td->td_base_pri;
  760         td->td_priority = pri;
  761 
  762         if (LOCK_LOG_TEST(&m->mtx_object, opts))
  763                 CTR2(KTR_LOCK, "_mtx_unlock_sleep: %p contested setrunqueue %p",
  764                     m, td1);
  765 
  766         td1->td_blocked = NULL;
  767         TD_CLR_LOCK(td1);
  768         if (!TD_CAN_RUN(td1)) {
  769                 mtx_unlock_spin(&sched_lock);
  770                 return;
  771         }
  772         setrunqueue(td1);
  773 
  774         if (td->td_critnest == 1 && td1->td_priority < pri) {
  775 #ifdef notyet
  776                 if (td->td_ithd != NULL) {
  777                         struct ithd *it = td->td_ithd;
  778 
  779                         if (it->it_interrupted) {
  780                                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  781                                         CTR2(KTR_LOCK,
  782                                     "_mtx_unlock_sleep: %p interrupted %p",
  783                                             it, it->it_interrupted);
  784                                 intr_thd_fixup(it);
  785                         }
  786                 }
  787 #endif
  788                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  789                         CTR2(KTR_LOCK,
  790                             "_mtx_unlock_sleep: %p switching out lock=%p", m,
  791                             (void *)m->mtx_lock);
  792 
  793                 td->td_proc->p_stats->p_ru.ru_nivcsw++;
  794                 mi_switch();
  795                 if (LOCK_LOG_TEST(&m->mtx_object, opts))
  796                         CTR2(KTR_LOCK, "_mtx_unlock_sleep: %p resuming lock=%p",
  797                             m, (void *)m->mtx_lock);
  798         }
  799 
  800         mtx_unlock_spin(&sched_lock);
  801 
  802         return;
  803 }
  804 
  805 /*
  806  * All the unlocking of MTX_SPIN locks is done inline.
  807  * See the _rel_spin_lock() macro for the details.
  808  */
  809 
  810 /*
  811  * The backing function for the INVARIANTS-enabled mtx_assert()
  812  */
  813 #ifdef INVARIANT_SUPPORT
  814 void
  815 _mtx_assert(struct mtx *m, int what, const char *file, int line)
  816 {
  817 
  818         if (panicstr != NULL)
  819                 return;
  820         switch (what) {
  821         case MA_OWNED:
  822         case MA_OWNED | MA_RECURSED:
  823         case MA_OWNED | MA_NOTRECURSED:
  824                 if (!mtx_owned(m))
  825                         panic("mutex %s not owned at %s:%d",
  826                             m->mtx_object.lo_name, file, line);
  827                 if (mtx_recursed(m)) {
  828                         if ((what & MA_NOTRECURSED) != 0)
  829                                 panic("mutex %s recursed at %s:%d",
  830                                     m->mtx_object.lo_name, file, line);
  831                 } else if ((what & MA_RECURSED) != 0) {
  832                         panic("mutex %s unrecursed at %s:%d",
  833                             m->mtx_object.lo_name, file, line);
  834                 }
  835                 break;
  836         case MA_NOTOWNED:
  837                 if (mtx_owned(m))
  838                         panic("mutex %s owned at %s:%d",
  839                             m->mtx_object.lo_name, file, line);
  840                 break;
  841         default:
  842                 panic("unknown mtx_assert at %s:%d", file, line);
  843         }
  844 }
  845 #endif
  846 
  847 /*
  848  * The MUTEX_DEBUG-enabled mtx_validate()
  849  *
  850  * Most of these checks have been moved off into the LO_INITIALIZED flag
  851  * maintained by the witness code.
  852  */
  853 #ifdef MUTEX_DEBUG
  854 
  855 void    mtx_validate(struct mtx *);
  856 
  857 void
  858 mtx_validate(struct mtx *m)
  859 {
  860 
  861 /*
  862  * XXX: When kernacc() does not require Giant we can reenable this check
  863  */
  864 #ifdef notyet
  865 /*
  866  * XXX - When kernacc() is fixed on the alpha to handle K0_SEG memory properly
  867  * we can re-enable the kernacc() checks.
  868  */
  869 #ifndef __alpha__
  870         /*
  871          * Can't call kernacc() from early init386(), especially when
  872          * initializing Giant mutex, because some stuff in kernacc()
  873          * requires Giant itself.
  874          */
  875         if (!cold)
  876                 if (!kernacc((caddr_t)m, sizeof(m),
  877                     VM_PROT_READ | VM_PROT_WRITE))
  878                         panic("Can't read and write to mutex %p", m);
  879 #endif
  880 #endif
  881 }
  882 #endif
  883 
  884 /*
  885  * General init routine used by the MTX_SYSINIT() macro.
  886  */
  887 void
  888 mtx_sysinit(void *arg)
  889 {
  890         struct mtx_args *margs = arg;
  891 
  892         mtx_init(margs->ma_mtx, margs->ma_desc, NULL, margs->ma_opts);
  893 }
  894 
  895 /*
  896  * Mutex initialization routine; initialize lock `m' of type contained in
  897  * `opts' with options contained in `opts' and name `name.'  The optional
  898  * lock type `type' is used as a general lock category name for use with
  899  * witness.
  900  */
  901 void
  902 mtx_init(struct mtx *m, const char *name, const char *type, int opts)
  903 {
  904         struct lock_object *lock;
  905 
  906         MPASS((opts & ~(MTX_SPIN | MTX_QUIET | MTX_RECURSE |
  907             MTX_SLEEPABLE | MTX_NOWITNESS | MTX_DUPOK)) == 0);
  908 
  909 #ifdef MUTEX_DEBUG
  910         /* Diagnostic and error correction */
  911         mtx_validate(m);
  912 #endif
  913 
  914         lock = &m->mtx_object;
  915         KASSERT((lock->lo_flags & LO_INITIALIZED) == 0,
  916             ("mutex %s %p already initialized", name, m));
  917         bzero(m, sizeof(*m));
  918         if (opts & MTX_SPIN)
  919                 lock->lo_class = &lock_class_mtx_spin;
  920         else
  921                 lock->lo_class = &lock_class_mtx_sleep;
  922         lock->lo_name = name;
  923         lock->lo_type = type != NULL ? type : name;
  924         if (opts & MTX_QUIET)
  925                 lock->lo_flags = LO_QUIET;
  926         if (opts & MTX_RECURSE)
  927                 lock->lo_flags |= LO_RECURSABLE;
  928         if (opts & MTX_SLEEPABLE)
  929                 lock->lo_flags |= LO_SLEEPABLE;
  930         if ((opts & MTX_NOWITNESS) == 0)
  931                 lock->lo_flags |= LO_WITNESS;
  932         if (opts & MTX_DUPOK)
  933                 lock->lo_flags |= LO_DUPOK;
  934 
  935         m->mtx_lock = MTX_UNOWNED;
  936         TAILQ_INIT(&m->mtx_blocked);
  937 
  938         LOCK_LOG_INIT(lock, opts);
  939 
  940         WITNESS_INIT(lock);
  941 }
  942 
  943 /*
  944  * Remove lock `m' from all_mtx queue.  We don't allow MTX_QUIET to be
  945  * passed in as a flag here because if the corresponding mtx_init() was
  946  * called with MTX_QUIET set, then it will already be set in the mutex's
  947  * flags.
  948  */
  949 void
  950 mtx_destroy(struct mtx *m)
  951 {
  952 
  953         LOCK_LOG_DESTROY(&m->mtx_object, 0);
  954 
  955         if (!mtx_owned(m))
  956                 MPASS(mtx_unowned(m));
  957         else {
  958                 MPASS((m->mtx_lock & (MTX_RECURSED|MTX_CONTESTED)) == 0);
  959 
  960                 /* Tell witness this isn't locked to make it happy. */
  961                 WITNESS_UNLOCK(&m->mtx_object, LOP_EXCLUSIVE, __FILE__,
  962                     __LINE__);
  963         }
  964 
  965         WITNESS_DESTROY(&m->mtx_object);
  966 }
  967 
  968 /*
  969  * Intialize the mutex code and system mutexes.  This is called from the MD
  970  * startup code prior to mi_startup().  The per-CPU data space needs to be
  971  * setup before this is called.
  972  */
  973 void
  974 mutex_init(void)
  975 {
  976 
  977         /* Setup thread0 so that mutexes work. */
  978         LIST_INIT(&thread0.td_contested);
  979 
  980         /*
  981          * Initialize mutexes.
  982          */
  983         mtx_init(&Giant, "Giant", NULL, MTX_DEF | MTX_RECURSE);
  984         mtx_init(&sched_lock, "sched lock", NULL, MTX_SPIN | MTX_RECURSE);
  985         mtx_init(&proc0.p_mtx, "process lock", NULL, MTX_DEF | MTX_DUPOK);
  986         mtx_lock(&Giant);
  987 }
  988 
  989 /*
  990  * Encapsulated Giant mutex routines.  These routines provide encapsulation
  991  * control for the Giant mutex, allowing sysctls to be used to turn on and
  992  * off Giant around certain subsystems.  The default value for the sysctls
  993  * are set to what developers believe is stable and working in regards to
  994  * the Giant pushdown.  Developers should not turn off Giant via these
  995  * sysctls unless they know what they are doing.
  996  *
  997  * Callers of mtx_lock_giant() are expected to pass the return value to an
  998  * accompanying mtx_unlock_giant() later on.  If multiple subsystems are
  999  * effected by a Giant wrap, all related sysctl variables must be zero for
 1000  * the subsystem call to operate without Giant (as determined by the caller).
 1001  */
 1002 
 1003 SYSCTL_NODE(_kern, OID_AUTO, giant, CTLFLAG_RD, NULL, "Giant mutex manipulation");
 1004 
 1005 static int kern_giant_all = 0;
 1006 SYSCTL_INT(_kern_giant, OID_AUTO, all, CTLFLAG_RW, &kern_giant_all, 0, "");
 1007 
 1008 int kern_giant_proc = 1;        /* Giant around PROC locks */
 1009 int kern_giant_file = 1;        /* Giant around struct file & filedesc */
 1010 int kern_giant_ucred = 1;       /* Giant around ucred */
 1011 SYSCTL_INT(_kern_giant, OID_AUTO, proc, CTLFLAG_RW, &kern_giant_proc, 0, "");
 1012 SYSCTL_INT(_kern_giant, OID_AUTO, file, CTLFLAG_RW, &kern_giant_file, 0, "");
 1013 SYSCTL_INT(_kern_giant, OID_AUTO, ucred, CTLFLAG_RW, &kern_giant_ucred, 0, "");
 1014 
 1015 int
 1016 mtx_lock_giant(int sysctlvar)
 1017 {
 1018         if (sysctlvar || kern_giant_all) {
 1019                 mtx_lock(&Giant);
 1020                 return(1);
 1021         }
 1022         return(0);
 1023 }
 1024 
 1025 void
 1026 mtx_unlock_giant(int s)
 1027 {
 1028         if (s)
 1029                 mtx_unlock(&Giant);
 1030 }

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