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  * Copyright (c) 2000 Jake Burkholder <jake@freebsd.org>.
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD: releng/10.4/sys/kern/kern_condvar.c 302234 2016-06-27 21:50:30Z bdrewery $");
   29 
   30 #include "opt_ktrace.h"
   31 
   32 #include <sys/param.h>
   33 #include <sys/systm.h>
   34 #include <sys/limits.h>
   35 #include <sys/lock.h>
   36 #include <sys/mutex.h>
   37 #include <sys/proc.h>
   38 #include <sys/kernel.h>
   39 #include <sys/ktr.h>
   40 #include <sys/condvar.h>
   41 #include <sys/sched.h>
   42 #include <sys/signalvar.h>
   43 #include <sys/sleepqueue.h>
   44 #include <sys/resourcevar.h>
   45 #ifdef KTRACE
   46 #include <sys/uio.h>
   47 #include <sys/ktrace.h>
   48 #endif
   49 
   50 /*
   51  * A bound below which cv_waiters is valid.  Once cv_waiters reaches this bound,
   52  * cv_signal must manually check the wait queue for threads.
   53  */
   54 #define CV_WAITERS_BOUND        INT_MAX
   55 
   56 #define CV_WAITERS_INC(cvp) do {                                        \
   57         if ((cvp)->cv_waiters < CV_WAITERS_BOUND)                       \
   58                 (cvp)->cv_waiters++;                                    \
   59 } while (0)
   60 
   61 /*
   62  * Common sanity checks for cv_wait* functions.
   63  */
   64 #define CV_ASSERT(cvp, lock, td) do {                                   \
   65         KASSERT((td) != NULL, ("%s: td NULL", __func__));               \
   66         KASSERT(TD_IS_RUNNING(td), ("%s: not TDS_RUNNING", __func__));  \
   67         KASSERT((cvp) != NULL, ("%s: cvp NULL", __func__));             \
   68         KASSERT((lock) != NULL, ("%s: lock NULL", __func__));           \
   69 } while (0)
   70 
   71 /*
   72  * Initialize a condition variable.  Must be called before use.
   73  */
   74 void
   75 cv_init(struct cv *cvp, const char *desc)
   76 {
   77 
   78         cvp->cv_description = desc;
   79         cvp->cv_waiters = 0;
   80 }
   81 
   82 /*
   83  * Destroy a condition variable.  The condition variable must be re-initialized
   84  * in order to be re-used.
   85  */
   86 void
   87 cv_destroy(struct cv *cvp)
   88 {
   89 #ifdef INVARIANTS
   90         struct sleepqueue *sq;
   91 
   92         sleepq_lock(cvp);
   93         sq = sleepq_lookup(cvp);
   94         sleepq_release(cvp);
   95         KASSERT(sq == NULL, ("%s: associated sleep queue non-empty", __func__));
   96 #endif
   97 }
   98 
   99 /*
  100  * Wait on a condition variable.  The current thread is placed on the condition
  101  * variable's wait queue and suspended.  A cv_signal or cv_broadcast on the same
  102  * condition variable will resume the thread.  The mutex is released before
  103  * sleeping and will be held on return.  It is recommended that the mutex be
  104  * held when cv_signal or cv_broadcast are called.
  105  */
  106 void
  107 _cv_wait(struct cv *cvp, struct lock_object *lock)
  108 {
  109         WITNESS_SAVE_DECL(lock_witness);
  110         struct lock_class *class;
  111         struct thread *td;
  112         uintptr_t lock_state;
  113 
  114         td = curthread;
  115         lock_state = 0;
  116 #ifdef KTRACE
  117         if (KTRPOINT(td, KTR_CSW))
  118                 ktrcsw(1, 0, cv_wmesg(cvp));
  119 #endif
  120         CV_ASSERT(cvp, lock, td);
  121         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  122             "Waiting on \"%s\"", cvp->cv_description);
  123         class = LOCK_CLASS(lock);
  124 
  125         if (cold || panicstr) {
  126                 /*
  127                  * During autoconfiguration, just give interrupts
  128                  * a chance, then just return.  Don't run any other
  129                  * thread or panic below, in case this is the idle
  130                  * process and already asleep.
  131                  */
  132                 return;
  133         }
  134 
  135         sleepq_lock(cvp);
  136 
  137         CV_WAITERS_INC(cvp);
  138         if (lock == &Giant.lock_object)
  139                 mtx_assert(&Giant, MA_OWNED);
  140         DROP_GIANT();
  141 
  142         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  143         if (lock != &Giant.lock_object) {
  144                 if (class->lc_flags & LC_SLEEPABLE)
  145                         sleepq_release(cvp);
  146                 WITNESS_SAVE(lock, lock_witness);
  147                 lock_state = class->lc_unlock(lock);
  148                 if (class->lc_flags & LC_SLEEPABLE)
  149                         sleepq_lock(cvp);
  150         }
  151         sleepq_wait(cvp, 0);
  152 
  153 #ifdef KTRACE
  154         if (KTRPOINT(td, KTR_CSW))
  155                 ktrcsw(0, 0, cv_wmesg(cvp));
  156 #endif
  157         PICKUP_GIANT();
  158         if (lock != &Giant.lock_object) {
  159                 class->lc_lock(lock, lock_state);
  160                 WITNESS_RESTORE(lock, lock_witness);
  161         }
  162 }
  163 
  164 /*
  165  * Wait on a condition variable.  This function differs from cv_wait by
  166  * not acquiring the mutex after condition variable was signaled.
  167  */
  168 void
  169 _cv_wait_unlock(struct cv *cvp, struct lock_object *lock)
  170 {
  171         struct lock_class *class;
  172         struct thread *td;
  173 
  174         td = curthread;
  175 #ifdef KTRACE
  176         if (KTRPOINT(td, KTR_CSW))
  177                 ktrcsw(1, 0, cv_wmesg(cvp));
  178 #endif
  179         CV_ASSERT(cvp, lock, td);
  180         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  181             "Waiting on \"%s\"", cvp->cv_description);
  182         KASSERT(lock != &Giant.lock_object,
  183             ("cv_wait_unlock cannot be used with Giant"));
  184         class = LOCK_CLASS(lock);
  185 
  186         if (cold || panicstr) {
  187                 /*
  188                  * During autoconfiguration, just give interrupts
  189                  * a chance, then just return.  Don't run any other
  190                  * thread or panic below, in case this is the idle
  191                  * process and already asleep.
  192                  */
  193                 class->lc_unlock(lock);
  194                 return;
  195         }
  196 
  197         sleepq_lock(cvp);
  198 
  199         CV_WAITERS_INC(cvp);
  200         DROP_GIANT();
  201 
  202         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  203         if (class->lc_flags & LC_SLEEPABLE)
  204                 sleepq_release(cvp);
  205         class->lc_unlock(lock);
  206         if (class->lc_flags & LC_SLEEPABLE)
  207                 sleepq_lock(cvp);
  208         sleepq_wait(cvp, 0);
  209 
  210 #ifdef KTRACE
  211         if (KTRPOINT(td, KTR_CSW))
  212                 ktrcsw(0, 0, cv_wmesg(cvp));
  213 #endif
  214         PICKUP_GIANT();
  215 }
  216 
  217 /*
  218  * Wait on a condition variable, allowing interruption by signals.  Return 0 if
  219  * the thread was resumed with cv_signal or cv_broadcast, EINTR or ERESTART if
  220  * a signal was caught.  If ERESTART is returned the system call should be
  221  * restarted if possible.
  222  */
  223 int
  224 _cv_wait_sig(struct cv *cvp, struct lock_object *lock)
  225 {
  226         WITNESS_SAVE_DECL(lock_witness);
  227         struct lock_class *class;
  228         struct thread *td;
  229         uintptr_t lock_state;
  230         int rval;
  231 
  232         td = curthread;
  233         lock_state = 0;
  234 #ifdef KTRACE
  235         if (KTRPOINT(td, KTR_CSW))
  236                 ktrcsw(1, 0, cv_wmesg(cvp));
  237 #endif
  238         CV_ASSERT(cvp, lock, td);
  239         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  240             "Waiting on \"%s\"", cvp->cv_description);
  241         class = LOCK_CLASS(lock);
  242 
  243         if (cold || panicstr) {
  244                 /*
  245                  * After a panic, or during autoconfiguration, just give
  246                  * interrupts a chance, then just return; don't run any other
  247                  * procs or panic below, in case this is the idle process and
  248                  * already asleep.
  249                  */
  250                 return (0);
  251         }
  252 
  253         sleepq_lock(cvp);
  254 
  255         CV_WAITERS_INC(cvp);
  256         if (lock == &Giant.lock_object)
  257                 mtx_assert(&Giant, MA_OWNED);
  258         DROP_GIANT();
  259 
  260         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  261             SLEEPQ_INTERRUPTIBLE, 0);
  262         if (lock != &Giant.lock_object) {
  263                 if (class->lc_flags & LC_SLEEPABLE)
  264                         sleepq_release(cvp);
  265                 WITNESS_SAVE(lock, lock_witness);
  266                 lock_state = class->lc_unlock(lock);
  267                 if (class->lc_flags & LC_SLEEPABLE)
  268                         sleepq_lock(cvp);
  269         }
  270         rval = sleepq_wait_sig(cvp, 0);
  271 
  272 #ifdef KTRACE
  273         if (KTRPOINT(td, KTR_CSW))
  274                 ktrcsw(0, 0, cv_wmesg(cvp));
  275 #endif
  276         PICKUP_GIANT();
  277         if (lock != &Giant.lock_object) {
  278                 class->lc_lock(lock, lock_state);
  279                 WITNESS_RESTORE(lock, lock_witness);
  280         }
  281 
  282         return (rval);
  283 }
  284 
  285 /*
  286  * Wait on a condition variable for (at most) the value specified in sbt
  287  * argument. Returns 0 if the process was resumed by cv_signal or cv_broadcast,
  288  * EWOULDBLOCK if the timeout expires.
  289  */
  290 int
  291 _cv_timedwait_sbt(struct cv *cvp, struct lock_object *lock, sbintime_t sbt,
  292     sbintime_t pr, int flags)
  293 {
  294         WITNESS_SAVE_DECL(lock_witness);
  295         struct lock_class *class;
  296         struct thread *td;
  297         int lock_state, rval;
  298 
  299         td = curthread;
  300         lock_state = 0;
  301 #ifdef KTRACE
  302         if (KTRPOINT(td, KTR_CSW))
  303                 ktrcsw(1, 0, cv_wmesg(cvp));
  304 #endif
  305         CV_ASSERT(cvp, lock, td);
  306         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  307             "Waiting on \"%s\"", cvp->cv_description);
  308         class = LOCK_CLASS(lock);
  309 
  310         if (cold || panicstr) {
  311                 /*
  312                  * After a panic, or during autoconfiguration, just give
  313                  * interrupts a chance, then just return; don't run any other
  314                  * thread or panic below, in case this is the idle process and
  315                  * already asleep.
  316                  */
  317                 return 0;
  318         }
  319 
  320         sleepq_lock(cvp);
  321 
  322         CV_WAITERS_INC(cvp);
  323         if (lock == &Giant.lock_object)
  324                 mtx_assert(&Giant, MA_OWNED);
  325         DROP_GIANT();
  326 
  327         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
  328         sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
  329         if (lock != &Giant.lock_object) {
  330                 if (class->lc_flags & LC_SLEEPABLE)
  331                         sleepq_release(cvp);
  332                 WITNESS_SAVE(lock, lock_witness);
  333                 lock_state = class->lc_unlock(lock);
  334                 if (class->lc_flags & LC_SLEEPABLE)
  335                         sleepq_lock(cvp);
  336         }
  337         rval = sleepq_timedwait(cvp, 0);
  338 
  339 #ifdef KTRACE
  340         if (KTRPOINT(td, KTR_CSW))
  341                 ktrcsw(0, 0, cv_wmesg(cvp));
  342 #endif
  343         PICKUP_GIANT();
  344         if (lock != &Giant.lock_object) {
  345                 class->lc_lock(lock, lock_state);
  346                 WITNESS_RESTORE(lock, lock_witness);
  347         }
  348 
  349         return (rval);
  350 }
  351 
  352 /*
  353  * Wait on a condition variable for (at most) the value specified in sbt 
  354  * argument, allowing interruption by signals.
  355  * Returns 0 if the thread was resumed by cv_signal or cv_broadcast,
  356  * EWOULDBLOCK if the timeout expires, and EINTR or ERESTART if a signal
  357  * was caught.
  358  */
  359 int
  360 _cv_timedwait_sig_sbt(struct cv *cvp, struct lock_object *lock,
  361     sbintime_t sbt, sbintime_t pr, int flags)
  362 {
  363         WITNESS_SAVE_DECL(lock_witness);
  364         struct lock_class *class;
  365         struct thread *td;
  366         int lock_state, rval;
  367 
  368         td = curthread;
  369         lock_state = 0;
  370 #ifdef KTRACE
  371         if (KTRPOINT(td, KTR_CSW))
  372                 ktrcsw(1, 0, cv_wmesg(cvp));
  373 #endif
  374         CV_ASSERT(cvp, lock, td);
  375         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  376             "Waiting on \"%s\"", cvp->cv_description);
  377         class = LOCK_CLASS(lock);
  378 
  379         if (cold || panicstr) {
  380                 /*
  381                  * After a panic, or during autoconfiguration, just give
  382                  * interrupts a chance, then just return; don't run any other
  383                  * thread or panic below, in case this is the idle process and
  384                  * already asleep.
  385                  */
  386                 return 0;
  387         }
  388 
  389         sleepq_lock(cvp);
  390 
  391         CV_WAITERS_INC(cvp);
  392         if (lock == &Giant.lock_object)
  393                 mtx_assert(&Giant, MA_OWNED);
  394         DROP_GIANT();
  395 
  396         sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR |
  397             SLEEPQ_INTERRUPTIBLE, 0);
  398         sleepq_set_timeout_sbt(cvp, sbt, pr, flags);
  399         if (lock != &Giant.lock_object) {
  400                 if (class->lc_flags & LC_SLEEPABLE)
  401                         sleepq_release(cvp);
  402                 WITNESS_SAVE(lock, lock_witness);
  403                 lock_state = class->lc_unlock(lock);
  404                 if (class->lc_flags & LC_SLEEPABLE)
  405                         sleepq_lock(cvp);
  406         }
  407         rval = sleepq_timedwait_sig(cvp, 0);
  408 
  409 #ifdef KTRACE
  410         if (KTRPOINT(td, KTR_CSW))
  411                 ktrcsw(0, 0, cv_wmesg(cvp));
  412 #endif
  413         PICKUP_GIANT();
  414         if (lock != &Giant.lock_object) {
  415                 class->lc_lock(lock, lock_state);
  416                 WITNESS_RESTORE(lock, lock_witness);
  417         }
  418 
  419         return (rval);
  420 }
  421 
  422 /*
  423  * Signal a condition variable, wakes up one waiting thread.  Will also wakeup
  424  * the swapper if the process is not in memory, so that it can bring the
  425  * sleeping process in.  Note that this may also result in additional threads
  426  * being made runnable.  Should be called with the same mutex as was passed to
  427  * cv_wait held.
  428  */
  429 void
  430 cv_signal(struct cv *cvp)
  431 {
  432         int wakeup_swapper;
  433 
  434         wakeup_swapper = 0;
  435         sleepq_lock(cvp);
  436         if (cvp->cv_waiters > 0) {
  437                 if (cvp->cv_waiters == CV_WAITERS_BOUND &&
  438                     sleepq_lookup(cvp) == NULL) {
  439                         cvp->cv_waiters = 0;
  440                 } else {
  441                         if (cvp->cv_waiters < CV_WAITERS_BOUND)
  442                                 cvp->cv_waiters--;
  443                         wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0,
  444                             0);
  445                 }
  446         }
  447         sleepq_release(cvp);
  448         if (wakeup_swapper)
  449                 kick_proc0();
  450 }
  451 
  452 /*
  453  * Broadcast a signal to a condition variable.  Wakes up all waiting threads.
  454  * Should be called with the same mutex as was passed to cv_wait held.
  455  */
  456 void
  457 cv_broadcastpri(struct cv *cvp, int pri)
  458 {
  459         int wakeup_swapper;
  460 
  461         /*
  462          * XXX sleepq_broadcast pri argument changed from -1 meaning
  463          * no pri to 0 meaning no pri.
  464          */
  465         wakeup_swapper = 0;
  466         if (pri == -1)
  467                 pri = 0;
  468         sleepq_lock(cvp);
  469         if (cvp->cv_waiters > 0) {
  470                 cvp->cv_waiters = 0;
  471                 wakeup_swapper = sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0);
  472         }
  473         sleepq_release(cvp);
  474         if (wakeup_swapper)
  475                 kick_proc0();
  476 }

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