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


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

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    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 2000 Jake Burkholder <jake@freebsd.org>.
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``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 THE AUTHOR OR CONTRIBUTORS 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 
   29 #include <sys/cdefs.h>
   30 __FBSDID("$FreeBSD: releng/12.0/sys/kern/kern_condvar.c 326271 2017-11-27 15:20:12Z pfg $");
   31 
   32 #include "opt_ktrace.h"
   33 
   34 #include <sys/param.h>
   35 #include <sys/systm.h>
   36 #include <sys/limits.h>
   37 #include <sys/lock.h>
   38 #include <sys/mutex.h>
   39 #include <sys/proc.h>
   40 #include <sys/kernel.h>
   41 #include <sys/ktr.h>
   42 #include <sys/condvar.h>
   43 #include <sys/sched.h>
   44 #include <sys/signalvar.h>
   45 #include <sys/sleepqueue.h>
   46 #include <sys/resourcevar.h>
   47 #ifdef KTRACE
   48 #include <sys/uio.h>
   49 #include <sys/ktrace.h>
   50 #endif
   51 
   52 /*
   53  * A bound below which cv_waiters is valid.  Once cv_waiters reaches this bound,
   54  * cv_signal must manually check the wait queue for threads.
   55  */
   56 #define CV_WAITERS_BOUND        INT_MAX
   57 
   58 #define CV_WAITERS_INC(cvp) do {                                        \
   59         if ((cvp)->cv_waiters < CV_WAITERS_BOUND)                       \
   60                 (cvp)->cv_waiters++;                                    \
   61 } while (0)
   62 
   63 /*
   64  * Common sanity checks for cv_wait* functions.
   65  */
   66 #define CV_ASSERT(cvp, lock, td) do {                                   \
   67         KASSERT((td) != NULL, ("%s: td NULL", __func__));               \
   68         KASSERT(TD_IS_RUNNING(td), ("%s: not TDS_RUNNING", __func__));  \
   69         KASSERT((cvp) != NULL, ("%s: cvp NULL", __func__));             \
   70         KASSERT((lock) != NULL, ("%s: lock NULL", __func__));           \
   71 } while (0)
   72 
   73 /*
   74  * Initialize a condition variable.  Must be called before use.
   75  */
   76 void
   77 cv_init(struct cv *cvp, const char *desc)
   78 {
   79 
   80         cvp->cv_description = desc;
   81         cvp->cv_waiters = 0;
   82 }
   83 
   84 /*
   85  * Destroy a condition variable.  The condition variable must be re-initialized
   86  * in order to be re-used.
   87  */
   88 void
   89 cv_destroy(struct cv *cvp)
   90 {
   91 #ifdef INVARIANTS
   92         struct sleepqueue *sq;
   93 
   94         sleepq_lock(cvp);
   95         sq = sleepq_lookup(cvp);
   96         sleepq_release(cvp);
   97         KASSERT(sq == NULL, ("%s: associated sleep queue non-empty", __func__));
   98 #endif
   99 }
  100 
  101 /*
  102  * Wait on a condition variable.  The current thread is placed on the condition
  103  * variable's wait queue and suspended.  A cv_signal or cv_broadcast on the same
  104  * condition variable will resume the thread.  The mutex is released before
  105  * sleeping and will be held on return.  It is recommended that the mutex be
  106  * held when cv_signal or cv_broadcast are called.
  107  */
  108 void
  109 _cv_wait(struct cv *cvp, struct lock_object *lock)
  110 {
  111         WITNESS_SAVE_DECL(lock_witness);
  112         struct lock_class *class;
  113         struct thread *td;
  114         uintptr_t lock_state;
  115 
  116         td = curthread;
  117         lock_state = 0;
  118 #ifdef KTRACE
  119         if (KTRPOINT(td, KTR_CSW))
  120                 ktrcsw(1, 0, cv_wmesg(cvp));
  121 #endif
  122         CV_ASSERT(cvp, lock, td);
  123         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  124             "Waiting on \"%s\"", cvp->cv_description);
  125         class = LOCK_CLASS(lock);
  126 
  127         if (SCHEDULER_STOPPED_TD(td))
  128                 return;
  129 
  130         sleepq_lock(cvp);
  131 
  132         CV_WAITERS_INC(cvp);
  133         if (lock == &Giant.lock_object)
  134                 mtx_assert(&Giant, MA_OWNED);
  135         DROP_GIANT();
  136 
  137         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  138         if (lock != &Giant.lock_object) {
  139                 if (class->lc_flags & LC_SLEEPABLE)
  140                         sleepq_release(cvp);
  141                 WITNESS_SAVE(lock, lock_witness);
  142                 lock_state = class->lc_unlock(lock);
  143                 if (class->lc_flags & LC_SLEEPABLE)
  144                         sleepq_lock(cvp);
  145         }
  146         sleepq_wait(cvp, 0);
  147 
  148 #ifdef KTRACE
  149         if (KTRPOINT(td, KTR_CSW))
  150                 ktrcsw(0, 0, cv_wmesg(cvp));
  151 #endif
  152         PICKUP_GIANT();
  153         if (lock != &Giant.lock_object) {
  154                 class->lc_lock(lock, lock_state);
  155                 WITNESS_RESTORE(lock, lock_witness);
  156         }
  157 }
  158 
  159 /*
  160  * Wait on a condition variable.  This function differs from cv_wait by
  161  * not acquiring the mutex after condition variable was signaled.
  162  */
  163 void
  164 _cv_wait_unlock(struct cv *cvp, struct lock_object *lock)
  165 {
  166         struct lock_class *class;
  167         struct thread *td;
  168 
  169         td = curthread;
  170 #ifdef KTRACE
  171         if (KTRPOINT(td, KTR_CSW))
  172                 ktrcsw(1, 0, cv_wmesg(cvp));
  173 #endif
  174         CV_ASSERT(cvp, lock, td);
  175         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  176             "Waiting on \"%s\"", cvp->cv_description);
  177         KASSERT(lock != &Giant.lock_object,
  178             ("cv_wait_unlock cannot be used with Giant"));
  179         class = LOCK_CLASS(lock);
  180 
  181         if (SCHEDULER_STOPPED_TD(td)) {
  182                 class->lc_unlock(lock);
  183                 return;
  184         }
  185 
  186         sleepq_lock(cvp);
  187 
  188         CV_WAITERS_INC(cvp);
  189         DROP_GIANT();
  190 
  191         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  192         if (class->lc_flags & LC_SLEEPABLE)
  193                 sleepq_release(cvp);
  194         class->lc_unlock(lock);
  195         if (class->lc_flags & LC_SLEEPABLE)
  196                 sleepq_lock(cvp);
  197         sleepq_wait(cvp, 0);
  198 
  199 #ifdef KTRACE
  200         if (KTRPOINT(td, KTR_CSW))
  201                 ktrcsw(0, 0, cv_wmesg(cvp));
  202 #endif
  203         PICKUP_GIANT();
  204 }
  205 
  206 /*
  207  * Wait on a condition variable, allowing interruption by signals.  Return 0 if
  208  * the thread was resumed with cv_signal or cv_broadcast, EINTR or ERESTART if
  209  * a signal was caught.  If ERESTART is returned the system call should be
  210  * restarted if possible.
  211  */
  212 int
  213 _cv_wait_sig(struct cv *cvp, struct lock_object *lock)
  214 {
  215         WITNESS_SAVE_DECL(lock_witness);
  216         struct lock_class *class;
  217         struct thread *td;
  218         uintptr_t lock_state;
  219         int rval;
  220 
  221         td = curthread;
  222         lock_state = 0;
  223 #ifdef KTRACE
  224         if (KTRPOINT(td, KTR_CSW))
  225                 ktrcsw(1, 0, cv_wmesg(cvp));
  226 #endif
  227         CV_ASSERT(cvp, lock, td);
  228         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  229             "Waiting on \"%s\"", cvp->cv_description);
  230         class = LOCK_CLASS(lock);
  231 
  232         if (SCHEDULER_STOPPED_TD(td))
  233                 return (0);
  234 
  235         sleepq_lock(cvp);
  236 
  237         CV_WAITERS_INC(cvp);
  238         if (lock == &Giant.lock_object)
  239                 mtx_assert(&Giant, MA_OWNED);
  240         DROP_GIANT();
  241 
  242         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  243             SLEEPQ_INTERRUPTIBLE, 0);
  244         if (lock != &Giant.lock_object) {
  245                 if (class->lc_flags & LC_SLEEPABLE)
  246                         sleepq_release(cvp);
  247                 WITNESS_SAVE(lock, lock_witness);
  248                 lock_state = class->lc_unlock(lock);
  249                 if (class->lc_flags & LC_SLEEPABLE)
  250                         sleepq_lock(cvp);
  251         }
  252         rval = sleepq_wait_sig(cvp, 0);
  253 
  254 #ifdef KTRACE
  255         if (KTRPOINT(td, KTR_CSW))
  256                 ktrcsw(0, 0, cv_wmesg(cvp));
  257 #endif
  258         PICKUP_GIANT();
  259         if (lock != &Giant.lock_object) {
  260                 class->lc_lock(lock, lock_state);
  261                 WITNESS_RESTORE(lock, lock_witness);
  262         }
  263 
  264         return (rval);
  265 }
  266 
  267 /*
  268  * Wait on a condition variable for (at most) the value specified in sbt
  269  * argument. Returns 0 if the process was resumed by cv_signal or cv_broadcast,
  270  * EWOULDBLOCK if the timeout expires.
  271  */
  272 int
  273 _cv_timedwait_sbt(struct cv *cvp, struct lock_object *lock, sbintime_t sbt,
  274     sbintime_t pr, int flags)
  275 {
  276         WITNESS_SAVE_DECL(lock_witness);
  277         struct lock_class *class;
  278         struct thread *td;
  279         int lock_state, rval;
  280 
  281         td = curthread;
  282         lock_state = 0;
  283 #ifdef KTRACE
  284         if (KTRPOINT(td, KTR_CSW))
  285                 ktrcsw(1, 0, cv_wmesg(cvp));
  286 #endif
  287         CV_ASSERT(cvp, lock, td);
  288         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  289             "Waiting on \"%s\"", cvp->cv_description);
  290         class = LOCK_CLASS(lock);
  291 
  292         if (SCHEDULER_STOPPED_TD(td))
  293                 return (0);
  294 
  295         sleepq_lock(cvp);
  296 
  297         CV_WAITERS_INC(cvp);
  298         if (lock == &Giant.lock_object)
  299                 mtx_assert(&Giant, MA_OWNED);
  300         DROP_GIANT();
  301 
  302         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  303         sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
  304         if (lock != &Giant.lock_object) {
  305                 if (class->lc_flags & LC_SLEEPABLE)
  306                         sleepq_release(cvp);
  307                 WITNESS_SAVE(lock, lock_witness);
  308                 lock_state = class->lc_unlock(lock);
  309                 if (class->lc_flags & LC_SLEEPABLE)
  310                         sleepq_lock(cvp);
  311         }
  312         rval = sleepq_timedwait(cvp, 0);
  313 
  314 #ifdef KTRACE
  315         if (KTRPOINT(td, KTR_CSW))
  316                 ktrcsw(0, 0, cv_wmesg(cvp));
  317 #endif
  318         PICKUP_GIANT();
  319         if (lock != &Giant.lock_object) {
  320                 class->lc_lock(lock, lock_state);
  321                 WITNESS_RESTORE(lock, lock_witness);
  322         }
  323 
  324         return (rval);
  325 }
  326 
  327 /*
  328  * Wait on a condition variable for (at most) the value specified in sbt 
  329  * argument, allowing interruption by signals.
  330  * Returns 0 if the thread was resumed by cv_signal or cv_broadcast,
  331  * EWOULDBLOCK if the timeout expires, and EINTR or ERESTART if a signal
  332  * was caught.
  333  */
  334 int
  335 _cv_timedwait_sig_sbt(struct cv *cvp, struct lock_object *lock,
  336     sbintime_t sbt, sbintime_t pr, int flags)
  337 {
  338         WITNESS_SAVE_DECL(lock_witness);
  339         struct lock_class *class;
  340         struct thread *td;
  341         int lock_state, rval;
  342 
  343         td = curthread;
  344         lock_state = 0;
  345 #ifdef KTRACE
  346         if (KTRPOINT(td, KTR_CSW))
  347                 ktrcsw(1, 0, cv_wmesg(cvp));
  348 #endif
  349         CV_ASSERT(cvp, lock, td);
  350         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  351             "Waiting on \"%s\"", cvp->cv_description);
  352         class = LOCK_CLASS(lock);
  353 
  354         if (SCHEDULER_STOPPED_TD(td))
  355                 return (0);
  356 
  357         sleepq_lock(cvp);
  358 
  359         CV_WAITERS_INC(cvp);
  360         if (lock == &Giant.lock_object)
  361                 mtx_assert(&Giant, MA_OWNED);
  362         DROP_GIANT();
  363 
  364         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  365             SLEEPQ_INTERRUPTIBLE, 0);
  366         sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
  367         if (lock != &Giant.lock_object) {
  368                 if (class->lc_flags & LC_SLEEPABLE)
  369                         sleepq_release(cvp);
  370                 WITNESS_SAVE(lock, lock_witness);
  371                 lock_state = class->lc_unlock(lock);
  372                 if (class->lc_flags & LC_SLEEPABLE)
  373                         sleepq_lock(cvp);
  374         }
  375         rval = sleepq_timedwait_sig(cvp, 0);
  376 
  377 #ifdef KTRACE
  378         if (KTRPOINT(td, KTR_CSW))
  379                 ktrcsw(0, 0, cv_wmesg(cvp));
  380 #endif
  381         PICKUP_GIANT();
  382         if (lock != &Giant.lock_object) {
  383                 class->lc_lock(lock, lock_state);
  384                 WITNESS_RESTORE(lock, lock_witness);
  385         }
  386 
  387         return (rval);
  388 }
  389 
  390 /*
  391  * Signal a condition variable, wakes up one waiting thread.  Will also wakeup
  392  * the swapper if the process is not in memory, so that it can bring the
  393  * sleeping process in.  Note that this may also result in additional threads
  394  * being made runnable.  Should be called with the same mutex as was passed to
  395  * cv_wait held.
  396  */
  397 void
  398 cv_signal(struct cv *cvp)
  399 {
  400         int wakeup_swapper;
  401 
  402         if (cvp->cv_waiters == 0)
  403                 return;
  404         wakeup_swapper = 0;
  405         sleepq_lock(cvp);
  406         if (cvp->cv_waiters > 0) {
  407                 if (cvp->cv_waiters == CV_WAITERS_BOUND &&
  408                     sleepq_lookup(cvp) == NULL) {
  409                         cvp->cv_waiters = 0;
  410                 } else {
  411                         if (cvp->cv_waiters < CV_WAITERS_BOUND)
  412                                 cvp->cv_waiters--;
  413                         wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0,
  414                             0);
  415                 }
  416         }
  417         sleepq_release(cvp);
  418         if (wakeup_swapper)
  419                 kick_proc0();
  420 }
  421 
  422 /*
  423  * Broadcast a signal to a condition variable.  Wakes up all waiting threads.
  424  * Should be called with the same mutex as was passed to cv_wait held.
  425  */
  426 void
  427 cv_broadcastpri(struct cv *cvp, int pri)
  428 {
  429         int wakeup_swapper;
  430 
  431         if (cvp->cv_waiters == 0)
  432                 return;
  433         /*
  434          * XXX sleepq_broadcast pri argument changed from -1 meaning
  435          * no pri to 0 meaning no pri.
  436          */
  437         wakeup_swapper = 0;
  438         if (pri == -1)
  439                 pri = 0;
  440         sleepq_lock(cvp);
  441         if (cvp->cv_waiters > 0) {
  442                 cvp->cv_waiters = 0;
  443                 wakeup_swapper = sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0);
  444         }
  445         sleepq_release(cvp);
  446         if (wakeup_swapper)
  447                 kick_proc0();
  448 }

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