The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]

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

Version: -  FREEBSD  -  FREEBSD-12-STABLE  -  FREEBSD-12-0  -  FREEBSD-11-STABLE  -  FREEBSD-11-2  -  FREEBSD-11-1  -  FREEBSD-11-0  -  FREEBSD-10-STABLE  -  FREEBSD-10-4  -  FREEBSD-10-3  -  FREEBSD-10-2  -  FREEBSD-10-1  -  FREEBSD-10-0  -  FREEBSD-9-STABLE  -  FREEBSD-9-3  -  FREEBSD-9-2  -  FREEBSD-9-1  -  FREEBSD-9-0  -  FREEBSD-8-STABLE  -  FREEBSD-8-4  -  FREEBSD-8-3  -  FREEBSD-8-2  -  FREEBSD-8-1  -  FREEBSD-8-0  -  FREEBSD-7-STABLE  -  FREEBSD-7-4  -  FREEBSD-7-3  -  FREEBSD-7-2  -  FREEBSD-7-1  -  FREEBSD-7-0  -  FREEBSD-6-STABLE  -  FREEBSD-6-4  -  FREEBSD-6-3  -  FREEBSD-6-2  -  FREEBSD-6-1  -  FREEBSD-6-0  -  FREEBSD-5-STABLE  -  FREEBSD-5-5  -  FREEBSD-5-4  -  FREEBSD-5-3  -  FREEBSD-5-2  -  FREEBSD-5-1  -  FREEBSD-5-0  -  FREEBSD-4-STABLE  -  FREEBSD-3-STABLE  -  FREEBSD22  -  linux-2.6  -  linux-2.4.22  -  MK83  -  MK84  -  PLAN9  -  DFBSD  -  NETBSD  -  NETBSD5  -  NETBSD4  -  NETBSD3  -  NETBSD20  -  OPENBSD  -  xnu-517  -  xnu-792  -  xnu-792.6.70  -  xnu-1228  -  xnu-1456.1.26  -  xnu-1699.24.8  -  xnu-2050.18.24  -  OPENSOLARIS  -  minix-3-1-1 
SearchContext: -  none  -  3  -  10 

    1 /*-
    2  * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
    3  * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
    4  * All rights reserved.
    5  *
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice(s), this list of conditions and the following disclaimer as
   11  *    the first lines of this file unmodified other than the possible
   12  *    addition of one or more copyright notices.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice(s), this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
   18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
   19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   20  * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
   21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
   22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   23  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   24  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
   27  * DAMAGE.
   28  */
   29 
   30 /*
   31  * Shared/exclusive locks.  This implementation attempts to ensure
   32  * deterministic lock granting behavior, so that slocks and xlocks are
   33  * interleaved.
   34  *
   35  * Priority propagation will not generally raise the priority of lock holders,
   36  * so should not be relied upon in combination with sx locks.
   37  */
   38 
   39 #include "opt_ddb.h"
   40 #include "opt_hwpmc_hooks.h"
   41 #include "opt_kdtrace.h"
   42 #include "opt_no_adaptive_sx.h"
   43 
   44 #include <sys/cdefs.h>
   45 __FBSDID("$FreeBSD: stable/10/sys/kern/kern_sx.c 323870 2017-09-21 19:24:11Z marius $");
   46 
   47 #include <sys/param.h>
   48 #include <sys/systm.h>
   49 #include <sys/kdb.h>
   50 #include <sys/kernel.h>
   51 #include <sys/ktr.h>
   52 #include <sys/lock.h>
   53 #include <sys/mutex.h>
   54 #include <sys/proc.h>
   55 #include <sys/sched.h>
   56 #include <sys/sleepqueue.h>
   57 #include <sys/sx.h>
   58 #include <sys/smp.h>
   59 #include <sys/sysctl.h>
   60 
   61 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
   62 #include <machine/cpu.h>
   63 #endif
   64 
   65 #ifdef DDB
   66 #include <ddb/ddb.h>
   67 #endif
   68 
   69 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
   70 #define ADAPTIVE_SX
   71 #endif
   72 
   73 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
   74 
   75 #ifdef HWPMC_HOOKS
   76 #include <sys/pmckern.h>
   77 PMC_SOFT_DECLARE( , , lock, failed);
   78 #endif
   79 
   80 /* Handy macros for sleep queues. */
   81 #define SQ_EXCLUSIVE_QUEUE      0
   82 #define SQ_SHARED_QUEUE         1
   83 
   84 /*
   85  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
   86  * drop Giant anytime we have to sleep or if we adaptively spin.
   87  */
   88 #define GIANT_DECLARE                                                   \
   89         int _giantcnt = 0;                                              \
   90         WITNESS_SAVE_DECL(Giant)                                        \
   91 
   92 #define GIANT_SAVE() do {                                               \
   93         if (mtx_owned(&Giant)) {                                        \
   94                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
   95                 while (mtx_owned(&Giant)) {                             \
   96                         _giantcnt++;                                    \
   97                         mtx_unlock(&Giant);                             \
   98                 }                                                       \
   99         }                                                               \
  100 } while (0)
  101 
  102 #define GIANT_RESTORE() do {                                            \
  103         if (_giantcnt > 0) {                                            \
  104                 mtx_assert(&Giant, MA_NOTOWNED);                        \
  105                 while (_giantcnt--)                                     \
  106                         mtx_lock(&Giant);                               \
  107                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
  108         }                                                               \
  109 } while (0)
  110 
  111 /*
  112  * Returns true if an exclusive lock is recursed.  It assumes
  113  * curthread currently has an exclusive lock.
  114  */
  115 #define sx_recurse              lock_object.lo_data
  116 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
  117 
  118 static void     assert_sx(const struct lock_object *lock, int what);
  119 #ifdef DDB
  120 static void     db_show_sx(const struct lock_object *lock);
  121 #endif
  122 static void     lock_sx(struct lock_object *lock, uintptr_t how);
  123 #ifdef KDTRACE_HOOKS
  124 static int      owner_sx(const struct lock_object *lock, struct thread **owner);
  125 #endif
  126 static uintptr_t unlock_sx(struct lock_object *lock);
  127 
  128 struct lock_class lock_class_sx = {
  129         .lc_name = "sx",
  130         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
  131         .lc_assert = assert_sx,
  132 #ifdef DDB
  133         .lc_ddb_show = db_show_sx,
  134 #endif
  135         .lc_lock = lock_sx,
  136         .lc_unlock = unlock_sx,
  137 #ifdef KDTRACE_HOOKS
  138         .lc_owner = owner_sx,
  139 #endif
  140 };
  141 
  142 #ifndef INVARIANTS
  143 #define _sx_assert(sx, what, file, line)
  144 #endif
  145 
  146 #ifdef ADAPTIVE_SX
  147 static u_int asx_retries = 10;
  148 static u_int asx_loops = 10000;
  149 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
  150 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
  151 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
  152 
  153 static struct lock_delay_config sx_delay = {
  154         .initial        = 1000,
  155         .step           = 500,
  156         .min            = 100,
  157         .max            = 5000,
  158 };
  159 
  160 SYSCTL_INT(_debug_sx, OID_AUTO, delay_initial, CTLFLAG_RW, &sx_delay.initial,
  161     0, "");
  162 SYSCTL_INT(_debug_sx, OID_AUTO, delay_step, CTLFLAG_RW, &sx_delay.step,
  163     0, "");
  164 SYSCTL_INT(_debug_sx, OID_AUTO, delay_min, CTLFLAG_RW, &sx_delay.min,
  165     0, "");
  166 SYSCTL_INT(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max,
  167     0, "");
  168 
  169 static void
  170 sx_delay_sysinit(void *dummy)
  171 {
  172 
  173         sx_delay.initial = mp_ncpus * 25;
  174         sx_delay.step = (mp_ncpus * 25) / 2;
  175         sx_delay.min = mp_ncpus * 5;
  176         sx_delay.max = mp_ncpus * 25 * 10;
  177 }
  178 LOCK_DELAY_SYSINIT(sx_delay_sysinit);
  179 #endif
  180 
  181 void
  182 assert_sx(const struct lock_object *lock, int what)
  183 {
  184 
  185         sx_assert((const struct sx *)lock, what);
  186 }
  187 
  188 void
  189 lock_sx(struct lock_object *lock, uintptr_t how)
  190 {
  191         struct sx *sx;
  192 
  193         sx = (struct sx *)lock;
  194         if (how)
  195                 sx_slock(sx);
  196         else
  197                 sx_xlock(sx);
  198 }
  199 
  200 uintptr_t
  201 unlock_sx(struct lock_object *lock)
  202 {
  203         struct sx *sx;
  204 
  205         sx = (struct sx *)lock;
  206         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
  207         if (sx_xlocked(sx)) {
  208                 sx_xunlock(sx);
  209                 return (0);
  210         } else {
  211                 sx_sunlock(sx);
  212                 return (1);
  213         }
  214 }
  215 
  216 #ifdef KDTRACE_HOOKS
  217 int
  218 owner_sx(const struct lock_object *lock, struct thread **owner)
  219 {
  220         const struct sx *sx = (const struct sx *)lock;
  221         uintptr_t x = sx->sx_lock;
  222 
  223         *owner = (struct thread *)SX_OWNER(x);
  224         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
  225             (*owner != NULL));
  226 }
  227 #endif
  228 
  229 void
  230 sx_sysinit(void *arg)
  231 {
  232         struct sx_args *sargs = arg;
  233 
  234         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
  235 }
  236 
  237 void
  238 sx_init_flags(struct sx *sx, const char *description, int opts)
  239 {
  240         int flags;
  241 
  242         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
  243             SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0);
  244         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
  245             ("%s: sx_lock not aligned for %s: %p", __func__, description,
  246             &sx->sx_lock));
  247 
  248         flags = LO_SLEEPABLE | LO_UPGRADABLE;
  249         if (opts & SX_DUPOK)
  250                 flags |= LO_DUPOK;
  251         if (opts & SX_NOPROFILE)
  252                 flags |= LO_NOPROFILE;
  253         if (!(opts & SX_NOWITNESS))
  254                 flags |= LO_WITNESS;
  255         if (opts & SX_RECURSE)
  256                 flags |= LO_RECURSABLE;
  257         if (opts & SX_QUIET)
  258                 flags |= LO_QUIET;
  259         if (opts & SX_NEW)
  260                 flags |= LO_NEW;
  261 
  262         flags |= opts & SX_NOADAPTIVE;
  263         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
  264         sx->sx_lock = SX_LOCK_UNLOCKED;
  265         sx->sx_recurse = 0;
  266 }
  267 
  268 void
  269 sx_destroy(struct sx *sx)
  270 {
  271 
  272         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
  273         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
  274         sx->sx_lock = SX_LOCK_DESTROYED;
  275         lock_destroy(&sx->lock_object);
  276 }
  277 
  278 int
  279 _sx_slock(struct sx *sx, int opts, const char *file, int line)
  280 {
  281         int error = 0;
  282 
  283         if (SCHEDULER_STOPPED())
  284                 return (0);
  285         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  286             ("sx_slock() by idle thread %p on sx %s @ %s:%d",
  287             curthread, sx->lock_object.lo_name, file, line));
  288         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  289             ("sx_slock() of destroyed sx @ %s:%d", file, line));
  290         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
  291         error = __sx_slock(sx, opts, file, line);
  292         if (!error) {
  293                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
  294                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
  295                 curthread->td_locks++;
  296         }
  297 
  298         return (error);
  299 }
  300 
  301 int
  302 sx_try_slock_(struct sx *sx, const char *file, int line)
  303 {
  304         uintptr_t x;
  305 
  306         if (SCHEDULER_STOPPED())
  307                 return (1);
  308 
  309         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  310             ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
  311             curthread, sx->lock_object.lo_name, file, line));
  312 
  313         for (;;) {
  314                 x = sx->sx_lock;
  315                 KASSERT(x != SX_LOCK_DESTROYED,
  316                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
  317                 if (!(x & SX_LOCK_SHARED))
  318                         break;
  319                 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
  320                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
  321                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
  322                         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE,
  323                             sx, 0, 0, file, line);
  324                         curthread->td_locks++;
  325                         return (1);
  326                 }
  327         }
  328 
  329         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
  330         return (0);
  331 }
  332 
  333 int
  334 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
  335 {
  336         int error = 0;
  337 
  338         if (SCHEDULER_STOPPED())
  339                 return (0);
  340         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  341             ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
  342             curthread, sx->lock_object.lo_name, file, line));
  343         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  344             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
  345         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
  346             line, NULL);
  347         error = __sx_xlock(sx, curthread, opts, file, line);
  348         if (!error) {
  349                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
  350                     file, line);
  351                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
  352                 curthread->td_locks++;
  353         }
  354 
  355         return (error);
  356 }
  357 
  358 int
  359 sx_try_xlock_(struct sx *sx, const char *file, int line)
  360 {
  361         int rval;
  362 
  363         if (SCHEDULER_STOPPED())
  364                 return (1);
  365 
  366         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
  367             ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
  368             curthread, sx->lock_object.lo_name, file, line));
  369         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  370             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
  371 
  372         if (sx_xlocked(sx) &&
  373             (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
  374                 sx->sx_recurse++;
  375                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
  376                 rval = 1;
  377         } else
  378                 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
  379                     (uintptr_t)curthread);
  380         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
  381         if (rval) {
  382                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
  383                     file, line);
  384                 if (!sx_recursed(sx))
  385                         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE,
  386                             sx, 0, 0, file, line);
  387                 curthread->td_locks++;
  388         }
  389 
  390         return (rval);
  391 }
  392 
  393 void
  394 _sx_sunlock(struct sx *sx, const char *file, int line)
  395 {
  396 
  397         if (SCHEDULER_STOPPED())
  398                 return;
  399         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  400             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
  401         _sx_assert(sx, SA_SLOCKED, file, line);
  402         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
  403         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
  404         __sx_sunlock(sx, file, line);
  405         LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
  406         curthread->td_locks--;
  407 }
  408 
  409 void
  410 _sx_xunlock(struct sx *sx, const char *file, int line)
  411 {
  412 
  413         if (SCHEDULER_STOPPED())
  414                 return;
  415         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  416             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
  417         _sx_assert(sx, SA_XLOCKED, file, line);
  418         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
  419         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
  420             line);
  421         if (!sx_recursed(sx))
  422                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
  423         __sx_xunlock(sx, curthread, file, line);
  424         curthread->td_locks--;
  425 }
  426 
  427 /*
  428  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
  429  * This will only succeed if this thread holds a single shared lock.
  430  * Return 1 if if the upgrade succeed, 0 otherwise.
  431  */
  432 int
  433 sx_try_upgrade_(struct sx *sx, const char *file, int line)
  434 {
  435         uintptr_t x;
  436         int success;
  437 
  438         if (SCHEDULER_STOPPED())
  439                 return (1);
  440 
  441         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  442             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
  443         _sx_assert(sx, SA_SLOCKED, file, line);
  444 
  445         /*
  446          * Try to switch from one shared lock to an exclusive lock.  We need
  447          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
  448          * we will wake up the exclusive waiters when we drop the lock.
  449          */
  450         x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
  451         success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
  452             (uintptr_t)curthread | x);
  453         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
  454         if (success) {
  455                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
  456                     file, line);
  457                 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
  458         }
  459         return (success);
  460 }
  461 
  462 /*
  463  * Downgrade an unrecursed exclusive lock into a single shared lock.
  464  */
  465 void
  466 sx_downgrade_(struct sx *sx, const char *file, int line)
  467 {
  468         uintptr_t x;
  469         int wakeup_swapper;
  470 
  471         if (SCHEDULER_STOPPED())
  472                 return;
  473 
  474         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  475             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
  476         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
  477 #ifndef INVARIANTS
  478         if (sx_recursed(sx))
  479                 panic("downgrade of a recursed lock");
  480 #endif
  481 
  482         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
  483 
  484         /*
  485          * Try to switch from an exclusive lock with no shared waiters
  486          * to one sharer with no shared waiters.  If there are
  487          * exclusive waiters, we don't need to lock the sleep queue so
  488          * long as we preserve the flag.  We do one quick try and if
  489          * that fails we grab the sleepq lock to keep the flags from
  490          * changing and do it the slow way.
  491          *
  492          * We have to lock the sleep queue if there are shared waiters
  493          * so we can wake them up.
  494          */
  495         x = sx->sx_lock;
  496         if (!(x & SX_LOCK_SHARED_WAITERS) &&
  497             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
  498             (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
  499                 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
  500                 return;
  501         }
  502 
  503         /*
  504          * Lock the sleep queue so we can read the waiters bits
  505          * without any races and wakeup any shared waiters.
  506          */
  507         sleepq_lock(&sx->lock_object);
  508 
  509         /*
  510          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
  511          * shared lock.  If there are any shared waiters, wake them up.
  512          */
  513         wakeup_swapper = 0;
  514         x = sx->sx_lock;
  515         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
  516             (x & SX_LOCK_EXCLUSIVE_WAITERS));
  517         if (x & SX_LOCK_SHARED_WAITERS)
  518                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
  519                     0, SQ_SHARED_QUEUE);
  520         sleepq_release(&sx->lock_object);
  521 
  522         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
  523         LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
  524 
  525         if (wakeup_swapper)
  526                 kick_proc0();
  527 }
  528 
  529 /*
  530  * This function represents the so-called 'hard case' for sx_xlock
  531  * operation.  All 'easy case' failures are redirected to this.  Note
  532  * that ideally this would be a static function, but it needs to be
  533  * accessible from at least sx.h.
  534  */
  535 int
  536 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
  537     int line)
  538 {
  539         GIANT_DECLARE;
  540 #ifdef ADAPTIVE_SX
  541         volatile struct thread *owner;
  542         u_int i, spintries = 0;
  543 #endif
  544         uintptr_t x;
  545 #ifdef LOCK_PROFILING
  546         uint64_t waittime = 0;
  547         int contested = 0;
  548 #endif
  549         int error = 0;
  550 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
  551         struct lock_delay_arg lda;
  552 #endif
  553 #ifdef  KDTRACE_HOOKS
  554         uintptr_t state;
  555         u_int sleep_cnt = 0;
  556         int64_t sleep_time = 0;
  557         int64_t all_time = 0;
  558 #endif
  559 
  560         if (SCHEDULER_STOPPED())
  561                 return (0);
  562 
  563 #if defined(ADAPTIVE_SX)
  564         lock_delay_arg_init(&lda, &sx_delay);
  565 #elif defined(KDTRACE_HOOKS)
  566         lock_delay_arg_init(&lda, NULL);
  567 #endif
  568 
  569         /* If we already hold an exclusive lock, then recurse. */
  570         if (sx_xlocked(sx)) {
  571                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
  572             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
  573                     sx->lock_object.lo_name, file, line));
  574                 sx->sx_recurse++;
  575                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
  576                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  577                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
  578                 return (0);
  579         }
  580 
  581         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  582                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
  583                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
  584 
  585 #ifdef KDTRACE_HOOKS
  586         all_time -= lockstat_nsecs(&sx->lock_object);
  587         state = sx->sx_lock;
  588 #endif
  589         for (;;) {
  590                 if (sx->sx_lock == SX_LOCK_UNLOCKED &&
  591                     atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
  592                         break;
  593 #ifdef KDTRACE_HOOKS
  594                 lda.spin_cnt++;
  595 #endif
  596 #ifdef HWPMC_HOOKS
  597                 PMC_SOFT_CALL( , , lock, failed);
  598 #endif
  599                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
  600                     &waittime);
  601 #ifdef ADAPTIVE_SX
  602                 /*
  603                  * If the lock is write locked and the owner is
  604                  * running on another CPU, spin until the owner stops
  605                  * running or the state of the lock changes.
  606                  */
  607                 x = sx->sx_lock;
  608                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
  609                         if ((x & SX_LOCK_SHARED) == 0) {
  610                                 x = SX_OWNER(x);
  611                                 owner = (struct thread *)x;
  612                                 if (TD_IS_RUNNING(owner)) {
  613                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  614                                                 CTR3(KTR_LOCK,
  615                                             "%s: spinning on %p held by %p",
  616                                                     __func__, sx, owner);
  617                                         KTR_STATE1(KTR_SCHED, "thread",
  618                                             sched_tdname(curthread), "spinning",
  619                                             "lockname:\"%s\"",
  620                                             sx->lock_object.lo_name);
  621                                         GIANT_SAVE();
  622                                         while (SX_OWNER(sx->sx_lock) == x &&
  623                                             TD_IS_RUNNING(owner))
  624                                                 lock_delay(&lda);
  625                                         KTR_STATE0(KTR_SCHED, "thread",
  626                                             sched_tdname(curthread), "running");
  627                                         continue;
  628                                 }
  629                         } else if (SX_SHARERS(x) && spintries < asx_retries) {
  630                                 KTR_STATE1(KTR_SCHED, "thread",
  631                                     sched_tdname(curthread), "spinning",
  632                                     "lockname:\"%s\"", sx->lock_object.lo_name);
  633                                 GIANT_SAVE();
  634                                 spintries++;
  635                                 for (i = 0; i < asx_loops; i++) {
  636                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  637                                                 CTR4(KTR_LOCK,
  638                                     "%s: shared spinning on %p with %u and %u",
  639                                                     __func__, sx, spintries, i);
  640                                         x = sx->sx_lock;
  641                                         if ((x & SX_LOCK_SHARED) == 0 ||
  642                                             SX_SHARERS(x) == 0)
  643                                                 break;
  644                                         cpu_spinwait();
  645 #ifdef KDTRACE_HOOKS
  646                                         lda.spin_cnt++;
  647 #endif
  648                                 }
  649                                 KTR_STATE0(KTR_SCHED, "thread",
  650                                     sched_tdname(curthread), "running");
  651                                 if (i != asx_loops)
  652                                         continue;
  653                         }
  654                 }
  655 #endif
  656 
  657                 sleepq_lock(&sx->lock_object);
  658                 x = sx->sx_lock;
  659 
  660                 /*
  661                  * If the lock was released while spinning on the
  662                  * sleep queue chain lock, try again.
  663                  */
  664                 if (x == SX_LOCK_UNLOCKED) {
  665                         sleepq_release(&sx->lock_object);
  666                         continue;
  667                 }
  668 
  669 #ifdef ADAPTIVE_SX
  670                 /*
  671                  * The current lock owner might have started executing
  672                  * on another CPU (or the lock could have changed
  673                  * owners) while we were waiting on the sleep queue
  674                  * chain lock.  If so, drop the sleep queue lock and try
  675                  * again.
  676                  */
  677                 if (!(x & SX_LOCK_SHARED) &&
  678                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
  679                         owner = (struct thread *)SX_OWNER(x);
  680                         if (TD_IS_RUNNING(owner)) {
  681                                 sleepq_release(&sx->lock_object);
  682                                 continue;
  683                         }
  684                 }
  685 #endif
  686 
  687                 /*
  688                  * If an exclusive lock was released with both shared
  689                  * and exclusive waiters and a shared waiter hasn't
  690                  * woken up and acquired the lock yet, sx_lock will be
  691                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
  692                  * If we see that value, try to acquire it once.  Note
  693                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
  694                  * as there are other exclusive waiters still.  If we
  695                  * fail, restart the loop.
  696                  */
  697                 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
  698                         if (atomic_cmpset_acq_ptr(&sx->sx_lock,
  699                             SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
  700                             tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
  701                                 sleepq_release(&sx->lock_object);
  702                                 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
  703                                     __func__, sx);
  704                                 break;
  705                         }
  706                         sleepq_release(&sx->lock_object);
  707                         continue;
  708                 }
  709 
  710                 /*
  711                  * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
  712                  * than loop back and retry.
  713                  */
  714                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
  715                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
  716                             x | SX_LOCK_EXCLUSIVE_WAITERS)) {
  717                                 sleepq_release(&sx->lock_object);
  718                                 continue;
  719                         }
  720                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  721                                 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
  722                                     __func__, sx);
  723                 }
  724 
  725                 /*
  726                  * Since we have been unable to acquire the exclusive
  727                  * lock and the exclusive waiters flag is set, we have
  728                  * to sleep.
  729                  */
  730                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  731                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
  732                             __func__, sx);
  733 
  734 #ifdef KDTRACE_HOOKS
  735                 sleep_time -= lockstat_nsecs(&sx->lock_object);
  736 #endif
  737                 GIANT_SAVE();
  738                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
  739                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
  740                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
  741                 if (!(opts & SX_INTERRUPTIBLE))
  742                         sleepq_wait(&sx->lock_object, 0);
  743                 else
  744                         error = sleepq_wait_sig(&sx->lock_object, 0);
  745 #ifdef KDTRACE_HOOKS
  746                 sleep_time += lockstat_nsecs(&sx->lock_object);
  747                 sleep_cnt++;
  748 #endif
  749                 if (error) {
  750                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  751                                 CTR2(KTR_LOCK,
  752                         "%s: interruptible sleep by %p suspended by signal",
  753                                     __func__, sx);
  754                         break;
  755                 }
  756                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  757                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
  758                             __func__, sx);
  759         }
  760 #ifdef KDTRACE_HOOKS
  761         all_time += lockstat_nsecs(&sx->lock_object);
  762         if (sleep_time)
  763                 LOCKSTAT_RECORD4(LS_SX_XLOCK_BLOCK, sx, sleep_time,
  764                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
  765                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
  766         if (lda.spin_cnt > sleep_cnt)
  767                 LOCKSTAT_RECORD4(LS_SX_XLOCK_SPIN, sx, all_time - sleep_time,
  768                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
  769                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
  770 #endif
  771         if (!error)
  772                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
  773                     contested, waittime, file, line);
  774         GIANT_RESTORE();
  775         return (error);
  776 }
  777 
  778 /*
  779  * This function represents the so-called 'hard case' for sx_xunlock
  780  * operation.  All 'easy case' failures are redirected to this.  Note
  781  * that ideally this would be a static function, but it needs to be
  782  * accessible from at least sx.h.
  783  */
  784 void
  785 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
  786 {
  787         uintptr_t x;
  788         int queue, wakeup_swapper;
  789 
  790         if (SCHEDULER_STOPPED())
  791                 return;
  792 
  793         MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
  794 
  795         /* If the lock is recursed, then unrecurse one level. */
  796         if (sx_xlocked(sx) && sx_recursed(sx)) {
  797                 if ((--sx->sx_recurse) == 0)
  798                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
  799                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  800                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
  801                 return;
  802         }
  803         MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
  804             SX_LOCK_EXCLUSIVE_WAITERS));
  805         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  806                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
  807 
  808         sleepq_lock(&sx->lock_object);
  809         x = SX_LOCK_UNLOCKED;
  810 
  811         /*
  812          * The wake up algorithm here is quite simple and probably not
  813          * ideal.  It gives precedence to shared waiters if they are
  814          * present.  For this condition, we have to preserve the
  815          * state of the exclusive waiters flag.
  816          * If interruptible sleeps left the shared queue empty avoid a
  817          * starvation for the threads sleeping on the exclusive queue by giving
  818          * them precedence and cleaning up the shared waiters bit anyway.
  819          */
  820         if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
  821             sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
  822                 queue = SQ_SHARED_QUEUE;
  823                 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
  824         } else
  825                 queue = SQ_EXCLUSIVE_QUEUE;
  826 
  827         /* Wake up all the waiters for the specific queue. */
  828         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  829                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
  830                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
  831                     "exclusive");
  832         atomic_store_rel_ptr(&sx->sx_lock, x);
  833         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
  834             queue);
  835         sleepq_release(&sx->lock_object);
  836         if (wakeup_swapper)
  837                 kick_proc0();
  838 }
  839 
  840 /*
  841  * This function represents the so-called 'hard case' for sx_slock
  842  * operation.  All 'easy case' failures are redirected to this.  Note
  843  * that ideally this would be a static function, but it needs to be
  844  * accessible from at least sx.h.
  845  */
  846 int
  847 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
  848 {
  849         GIANT_DECLARE;
  850 #ifdef ADAPTIVE_SX
  851         volatile struct thread *owner;
  852 #endif
  853 #ifdef LOCK_PROFILING
  854         uint64_t waittime = 0;
  855         int contested = 0;
  856 #endif
  857         uintptr_t x;
  858         int error = 0;
  859 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
  860         struct lock_delay_arg lda;
  861 #endif
  862 #ifdef KDTRACE_HOOKS
  863         uintptr_t state;
  864         u_int sleep_cnt = 0;
  865         int64_t sleep_time = 0;
  866         int64_t all_time = 0;
  867 #endif
  868 
  869         if (SCHEDULER_STOPPED())
  870                 return (0);
  871 
  872 #if defined(ADAPTIVE_SX)
  873         lock_delay_arg_init(&lda, &sx_delay);
  874 #elif defined(KDTRACE_HOOKS)
  875         lock_delay_arg_init(&lda, NULL);
  876 #endif
  877 #ifdef KDTRACE_HOOKS
  878         state = sx->sx_lock;
  879         all_time -= lockstat_nsecs(&sx->lock_object);
  880 #endif
  881 
  882         /*
  883          * As with rwlocks, we don't make any attempt to try to block
  884          * shared locks once there is an exclusive waiter.
  885          */
  886         for (;;) {
  887 #ifdef KDTRACE_HOOKS
  888                 lda.spin_cnt++;
  889 #endif
  890                 x = sx->sx_lock;
  891 
  892                 /*
  893                  * If no other thread has an exclusive lock then try to bump up
  894                  * the count of sharers.  Since we have to preserve the state
  895                  * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
  896                  * shared lock loop back and retry.
  897                  */
  898                 if (x & SX_LOCK_SHARED) {
  899                         MPASS(!(x & SX_LOCK_SHARED_WAITERS));
  900                         if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
  901                             x + SX_ONE_SHARER)) {
  902                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  903                                         CTR4(KTR_LOCK,
  904                                             "%s: %p succeed %p -> %p", __func__,
  905                                             sx, (void *)x,
  906                                             (void *)(x + SX_ONE_SHARER));
  907                                 break;
  908                         }
  909                         continue;
  910                 }
  911 #ifdef HWPMC_HOOKS
  912                 PMC_SOFT_CALL( , , lock, failed);
  913 #endif
  914                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
  915                     &waittime);
  916 
  917 #ifdef ADAPTIVE_SX
  918                 /*
  919                  * If the owner is running on another CPU, spin until
  920                  * the owner stops running or the state of the lock
  921                  * changes.
  922                  */
  923                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
  924                         x = SX_OWNER(x);
  925                         owner = (struct thread *)x;
  926                         if (TD_IS_RUNNING(owner)) {
  927                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  928                                         CTR3(KTR_LOCK,
  929                                             "%s: spinning on %p held by %p",
  930                                             __func__, sx, owner);
  931                                 KTR_STATE1(KTR_SCHED, "thread",
  932                                     sched_tdname(curthread), "spinning",
  933                                     "lockname:\"%s\"", sx->lock_object.lo_name);
  934                                 GIANT_SAVE();
  935                                 while (SX_OWNER(sx->sx_lock) == x &&
  936                                     TD_IS_RUNNING(owner))
  937                                         lock_delay(&lda);
  938                                 KTR_STATE0(KTR_SCHED, "thread",
  939                                     sched_tdname(curthread), "running");
  940                                 continue;
  941                         }
  942                 }
  943 #endif
  944 
  945                 /*
  946                  * Some other thread already has an exclusive lock, so
  947                  * start the process of blocking.
  948                  */
  949                 sleepq_lock(&sx->lock_object);
  950                 x = sx->sx_lock;
  951 
  952                 /*
  953                  * The lock could have been released while we spun.
  954                  * In this case loop back and retry.
  955                  */
  956                 if (x & SX_LOCK_SHARED) {
  957                         sleepq_release(&sx->lock_object);
  958                         continue;
  959                 }
  960 
  961 #ifdef ADAPTIVE_SX
  962                 /*
  963                  * If the owner is running on another CPU, spin until
  964                  * the owner stops running or the state of the lock
  965                  * changes.
  966                  */
  967                 if (!(x & SX_LOCK_SHARED) &&
  968                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
  969                         owner = (struct thread *)SX_OWNER(x);
  970                         if (TD_IS_RUNNING(owner)) {
  971                                 sleepq_release(&sx->lock_object);
  972                                 continue;
  973                         }
  974                 }
  975 #endif
  976 
  977                 /*
  978                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
  979                  * fail to set it drop the sleep queue lock and loop
  980                  * back.
  981                  */
  982                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
  983                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
  984                             x | SX_LOCK_SHARED_WAITERS)) {
  985                                 sleepq_release(&sx->lock_object);
  986                                 continue;
  987                         }
  988                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  989                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
  990                                     __func__, sx);
  991                 }
  992 
  993                 /*
  994                  * Since we have been unable to acquire the shared lock,
  995                  * we have to sleep.
  996                  */
  997                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  998                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
  999                             __func__, sx);
 1000 
 1001 #ifdef KDTRACE_HOOKS
 1002                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 1003 #endif
 1004                 GIANT_SAVE();
 1005                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 1006                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 1007                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
 1008                 if (!(opts & SX_INTERRUPTIBLE))
 1009                         sleepq_wait(&sx->lock_object, 0);
 1010                 else
 1011                         error = sleepq_wait_sig(&sx->lock_object, 0);
 1012 #ifdef KDTRACE_HOOKS
 1013                 sleep_time += lockstat_nsecs(&sx->lock_object);
 1014                 sleep_cnt++;
 1015 #endif
 1016                 if (error) {
 1017                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 1018                                 CTR2(KTR_LOCK,
 1019                         "%s: interruptible sleep by %p suspended by signal",
 1020                                     __func__, sx);
 1021                         break;
 1022                 }
 1023                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 1024                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 1025                             __func__, sx);
 1026         }
 1027 #ifdef KDTRACE_HOOKS
 1028         all_time += lockstat_nsecs(&sx->lock_object);
 1029         if (sleep_time)
 1030                 LOCKSTAT_RECORD4(LS_SX_SLOCK_BLOCK, sx, sleep_time,
 1031                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
 1032                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 1033         if (lda.spin_cnt > sleep_cnt)
 1034                 LOCKSTAT_RECORD4(LS_SX_SLOCK_SPIN, sx, all_time - sleep_time,
 1035                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
 1036                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 1037 #endif
 1038         if (error == 0)
 1039                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
 1040                     contested, waittime, file, line);
 1041         GIANT_RESTORE();
 1042         return (error);
 1043 }
 1044 
 1045 /*
 1046  * This function represents the so-called 'hard case' for sx_sunlock
 1047  * operation.  All 'easy case' failures are redirected to this.  Note
 1048  * that ideally this would be a static function, but it needs to be
 1049  * accessible from at least sx.h.
 1050  */
 1051 void
 1052 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
 1053 {
 1054         uintptr_t x;
 1055         int wakeup_swapper;
 1056 
 1057         if (SCHEDULER_STOPPED())
 1058                 return;
 1059 
 1060         for (;;) {
 1061                 x = sx->sx_lock;
 1062 
 1063                 /*
 1064                  * We should never have sharers while at least one thread
 1065                  * holds a shared lock.
 1066                  */
 1067                 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
 1068                     ("%s: waiting sharers", __func__));
 1069 
 1070                 /*
 1071                  * See if there is more than one shared lock held.  If
 1072                  * so, just drop one and return.
 1073                  */
 1074                 if (SX_SHARERS(x) > 1) {
 1075                         if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
 1076                             x - SX_ONE_SHARER)) {
 1077                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 1078                                         CTR4(KTR_LOCK,
 1079                                             "%s: %p succeeded %p -> %p",
 1080                                             __func__, sx, (void *)x,
 1081                                             (void *)(x - SX_ONE_SHARER));
 1082                                 break;
 1083                         }
 1084                         continue;
 1085                 }
 1086 
 1087                 /*
 1088                  * If there aren't any waiters for an exclusive lock,
 1089                  * then try to drop it quickly.
 1090                  */
 1091                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 1092                         MPASS(x == SX_SHARERS_LOCK(1));
 1093                         if (atomic_cmpset_rel_ptr(&sx->sx_lock,
 1094                             SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
 1095                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 1096                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
 1097                                             __func__, sx);
 1098                                 break;
 1099                         }
 1100                         continue;
 1101                 }
 1102 
 1103                 /*
 1104                  * At this point, there should just be one sharer with
 1105                  * exclusive waiters.
 1106                  */
 1107                 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
 1108 
 1109                 sleepq_lock(&sx->lock_object);
 1110 
 1111                 /*
 1112                  * Wake up semantic here is quite simple:
 1113                  * Just wake up all the exclusive waiters.
 1114                  * Note that the state of the lock could have changed,
 1115                  * so if it fails loop back and retry.
 1116                  */
 1117                 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
 1118                     SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
 1119                     SX_LOCK_UNLOCKED)) {
 1120                         sleepq_release(&sx->lock_object);
 1121                         continue;
 1122                 }
 1123                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 1124                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
 1125                             "exclusive queue", __func__, sx);
 1126                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 1127                     0, SQ_EXCLUSIVE_QUEUE);
 1128                 sleepq_release(&sx->lock_object);
 1129                 if (wakeup_swapper)
 1130                         kick_proc0();
 1131                 break;
 1132         }
 1133 }
 1134 
 1135 #ifdef INVARIANT_SUPPORT
 1136 #ifndef INVARIANTS
 1137 #undef  _sx_assert
 1138 #endif
 1139 
 1140 /*
 1141  * In the non-WITNESS case, sx_assert() can only detect that at least
 1142  * *some* thread owns an slock, but it cannot guarantee that *this*
 1143  * thread owns an slock.
 1144  */
 1145 void
 1146 _sx_assert(const struct sx *sx, int what, const char *file, int line)
 1147 {
 1148 #ifndef WITNESS
 1149         int slocked = 0;
 1150 #endif
 1151 
 1152         if (panicstr != NULL)
 1153                 return;
 1154         switch (what) {
 1155         case SA_SLOCKED:
 1156         case SA_SLOCKED | SA_NOTRECURSED:
 1157         case SA_SLOCKED | SA_RECURSED:
 1158 #ifndef WITNESS
 1159                 slocked = 1;
 1160                 /* FALLTHROUGH */
 1161 #endif
 1162         case SA_LOCKED:
 1163         case SA_LOCKED | SA_NOTRECURSED:
 1164         case SA_LOCKED | SA_RECURSED:
 1165 #ifdef WITNESS
 1166                 witness_assert(&sx->lock_object, what, file, line);
 1167 #else
 1168                 /*
 1169                  * If some other thread has an exclusive lock or we
 1170                  * have one and are asserting a shared lock, fail.
 1171                  * Also, if no one has a lock at all, fail.
 1172                  */
 1173                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
 1174                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
 1175                     sx_xholder(sx) != curthread)))
 1176                         panic("Lock %s not %slocked @ %s:%d\n",
 1177                             sx->lock_object.lo_name, slocked ? "share " : "",
 1178                             file, line);
 1179 
 1180                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
 1181                         if (sx_recursed(sx)) {
 1182                                 if (what & SA_NOTRECURSED)
 1183                                         panic("Lock %s recursed @ %s:%d\n",
 1184                                             sx->lock_object.lo_name, file,
 1185                                             line);
 1186                         } else if (what & SA_RECURSED)
 1187                                 panic("Lock %s not recursed @ %s:%d\n",
 1188                                     sx->lock_object.lo_name, file, line);
 1189                 }
 1190 #endif
 1191                 break;
 1192         case SA_XLOCKED:
 1193         case SA_XLOCKED | SA_NOTRECURSED:
 1194         case SA_XLOCKED | SA_RECURSED:
 1195                 if (sx_xholder(sx) != curthread)
 1196                         panic("Lock %s not exclusively locked @ %s:%d\n",
 1197                             sx->lock_object.lo_name, file, line);
 1198                 if (sx_recursed(sx)) {
 1199                         if (what & SA_NOTRECURSED)
 1200                                 panic("Lock %s recursed @ %s:%d\n",
 1201                                     sx->lock_object.lo_name, file, line);
 1202                 } else if (what & SA_RECURSED)
 1203                         panic("Lock %s not recursed @ %s:%d\n",
 1204                             sx->lock_object.lo_name, file, line);
 1205                 break;
 1206         case SA_UNLOCKED:
 1207 #ifdef WITNESS
 1208                 witness_assert(&sx->lock_object, what, file, line);
 1209 #else
 1210                 /*
 1211                  * If we hold an exclusve lock fail.  We can't
 1212                  * reliably check to see if we hold a shared lock or
 1213                  * not.
 1214                  */
 1215                 if (sx_xholder(sx) == curthread)
 1216                         panic("Lock %s exclusively locked @ %s:%d\n",
 1217                             sx->lock_object.lo_name, file, line);
 1218 #endif
 1219                 break;
 1220         default:
 1221                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
 1222                     line);
 1223         }
 1224 }
 1225 #endif  /* INVARIANT_SUPPORT */
 1226 
 1227 #ifdef DDB
 1228 static void
 1229 db_show_sx(const struct lock_object *lock)
 1230 {
 1231         struct thread *td;
 1232         const struct sx *sx;
 1233 
 1234         sx = (const struct sx *)lock;
 1235 
 1236         db_printf(" state: ");
 1237         if (sx->sx_lock == SX_LOCK_UNLOCKED)
 1238                 db_printf("UNLOCKED\n");
 1239         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
 1240                 db_printf("DESTROYED\n");
 1241                 return;
 1242         } else if (sx->sx_lock & SX_LOCK_SHARED)
 1243                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
 1244         else {
 1245                 td = sx_xholder(sx);
 1246                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
 1247                     td->td_tid, td->td_proc->p_pid, td->td_name);
 1248                 if (sx_recursed(sx))
 1249                         db_printf(" recursed: %d\n", sx->sx_recurse);
 1250         }
 1251 
 1252         db_printf(" waiters: ");
 1253         switch(sx->sx_lock &
 1254             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
 1255         case SX_LOCK_SHARED_WAITERS:
 1256                 db_printf("shared\n");
 1257                 break;
 1258         case SX_LOCK_EXCLUSIVE_WAITERS:
 1259                 db_printf("exclusive\n");
 1260                 break;
 1261         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
 1262                 db_printf("exclusive and shared\n");
 1263                 break;
 1264         default:
 1265                 db_printf("none\n");
 1266         }
 1267 }
 1268 
 1269 /*
 1270  * Check to see if a thread that is blocked on a sleep queue is actually
 1271  * blocked on an sx lock.  If so, output some details and return true.
 1272  * If the lock has an exclusive owner, return that in *ownerp.
 1273  */
 1274 int
 1275 sx_chain(struct thread *td, struct thread **ownerp)
 1276 {
 1277         struct sx *sx;
 1278 
 1279         /*
 1280          * Check to see if this thread is blocked on an sx lock.
 1281          * First, we check the lock class.  If that is ok, then we
 1282          * compare the lock name against the wait message.
 1283          */
 1284         sx = td->td_wchan;
 1285         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
 1286             sx->lock_object.lo_name != td->td_wmesg)
 1287                 return (0);
 1288 
 1289         /* We think we have an sx lock, so output some details. */
 1290         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
 1291         *ownerp = sx_xholder(sx);
 1292         if (sx->sx_lock & SX_LOCK_SHARED)
 1293                 db_printf("SLOCK (count %ju)\n",
 1294                     (uintmax_t)SX_SHARERS(sx->sx_lock));
 1295         else
 1296                 db_printf("XLOCK\n");
 1297         return (1);
 1298 }
 1299 #endif

Cache object: df84029ee0e0307fb6b226186c8277ec


[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]


This page is part of the FreeBSD/Linux Linux Kernel Cross-Reference, and was automatically generated using a modified version of the LXR engine.