kernel/os/semaphore.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21
  22 /*
  23  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26
  27 #pragma ident   "%Z%%M% %I%     %E% SMI"
  28
  29 /*
  30  * This file contains the semaphore operations.
  31  */
  32
  33 #include <sys/param.h>
  34 #include <sys/types.h>
  35 #include <sys/systm.h>
  36 #include <sys/schedctl.h>
  37 #include <sys/semaphore.h>
  38 #include <sys/sema_impl.h>
  39 #include <sys/t_lock.h>
  40 #include <sys/thread.h>
  41 #include <sys/proc.h>
  42 #include <sys/cmn_err.h>
  43 #include <sys/debug.h>
  44 #include <sys/disp.h>
  45 #include <sys/sobject.h>
  46 #include <sys/cpuvar.h>
  47 #include <sys/sleepq.h>
  48 #include <sys/sdt.h>
  49
  50 static void sema_unsleep(kthread_t *t);
  51 static void sema_change_pri(kthread_t *t, pri_t pri, pri_t *t_prip);
  52 static kthread_t *sema_owner(ksema_t *);
  53
  54 /*
  55  * The sobj_ops vector exports a set of functions needed when a thread
  56  * is asleep on a synchronization object of this type.
  57  */
  58 static sobj_ops_t sema_sobj_ops = {
  59         SOBJ_SEMA, sema_owner, sema_unsleep, sema_change_pri
  60 };
  61
  62 /*
  63  * SEMA_BLOCK(sema_impl_t *s, disp_lock_t *lockp)
  64  */
  65 #define SEMA_BLOCK(s, lockp)                                            \
  66         {                                                               \
  67                 kthread_t       *tp;                                    \
  68                 kthread_t       **tpp;                                  \
  69                 pri_t           cpri;                                   \
  70                 klwp_t  *lwp = ttolwp(curthread);                       \
  71                 ASSERT(THREAD_LOCK_HELD(curthread));                    \
  72                 ASSERT(curthread != CPU->cpu_idle_thread);              \
  73                 ASSERT(CPU_ON_INTR(CPU) == 0);                          \
  74                 ASSERT(curthread->t_wchan0 == NULL);                    \
  75                 ASSERT(curthread->t_wchan == NULL);                     \
  76                 ASSERT(curthread->t_state == TS_ONPROC);                \
  77                 CL_SLEEP(curthread);                                    \
  78                 THREAD_SLEEP(curthread, lockp);                         \
  79                 curthread->t_wchan = (caddr_t)s;                        \
  80                 curthread->t_sobj_ops = &sema_sobj_ops;                 \
  81                 DTRACE_SCHED(sleep);                                    \
  82                 if (lwp != NULL) {                                      \
  83                         lwp->lwp_ru.nvcsw++;                            \
  84                         (void) new_mstate(curthread, LMS_SLEEP);        \
  85                 }                                                       \
  86                 cpri = DISP_PRIO(curthread);                            \
  87                 tpp = &s->s_slpq;                                       \
  88                 while ((tp = *tpp) != NULL) {                           \
  89                         if (cpri > DISP_PRIO(tp))                       \
  90                                 break;                                  \
  91                         tpp = &tp->t_link;                              \
  92                 }                                                       \
  93                 *tpp = curthread;                                       \
  94                 curthread->t_link = tp;                                 \
  95                 ASSERT(s->s_slpq != NULL);                              \
  96         }
  97
  98 /* ARGSUSED */
  99 void
 100 sema_init(ksema_t *sp, unsigned count, char *name, ksema_type_t type, void *arg)
 101 {
 102         ((sema_impl_t *)sp)->s_count = count;
 103         ((sema_impl_t *)sp)->s_slpq = NULL;
 104 }
 105
 106 void
 107 sema_destroy(ksema_t *sp)
 108 {
 109         ASSERT(((sema_impl_t *)sp)->s_slpq == NULL);
 110 }
 111
 112 /*
 113  * Put a thread on the sleep queue for this semaphore.
 114  */
 115 static void
 116 sema_queue(ksema_t *sp, kthread_t *t)
 117 {
 118         kthread_t       **tpp;
 119         kthread_t       *tp;
 120         pri_t           cpri;
 121         sema_impl_t     *s;
 122
 123         ASSERT(THREAD_LOCK_HELD(t));
 124         s = (sema_impl_t *)sp;
 125         tpp = &s->s_slpq;
 126         cpri = DISP_PRIO(t);
 127         while ((tp = *tpp) != NULL) {
 128                 if (cpri > DISP_PRIO(tp))
 129                         break;
 130                 tpp = &tp->t_link;
 131         }
 132         *tpp = t;
 133         t->t_link = tp;
 134 }
 135
 136 /*
 137  * Remove a thread from the sleep queue for this
 138  * semaphore.
 139  */
 140 static void
 141 sema_dequeue(ksema_t *sp, kthread_t *t)
 142 {
 143         kthread_t       **tpp;
 144         kthread_t       *tp;
 145         sema_impl_t     *s;
 146
 147         ASSERT(THREAD_LOCK_HELD(t));
 148         s = (sema_impl_t *)sp;
 149         tpp = &s->s_slpq;
 150         while ((tp = *tpp) != NULL) {
 151                 if (tp == t) {
 152                         *tpp = t->t_link;
 153                         t->t_link = NULL;
 154                         return;
 155                 }
 156                 tpp = &tp->t_link;
 157         }
 158 }
 159
 160 /* ARGSUSED */
 161 static kthread_t *
 162 sema_owner(ksema_t *sp)
 163 {
 164         return (NULL);
 165 }
 166
 167 /*
 168  * Wakeup a thread sleeping on a semaphore, and put it
 169  * on the dispatch queue.
 170  * Called via SOBJ_UNSLEEP().
 171  */
 172 static void
 173 sema_unsleep(kthread_t *t)
 174 {
 175         kthread_t       **tpp;
 176         kthread_t       *tp;
 177         sema_impl_t     *s;
 178
 179         ASSERT(THREAD_LOCK_HELD(t));
 180         s = (sema_impl_t *)t->t_wchan;
 181         tpp = &s->s_slpq;
 182         while ((tp = *tpp) != NULL) {
 183                 if (tp == t) {
 184                         *tpp = t->t_link;
 185                         t->t_link = NULL;
 186                         t->t_sobj_ops = NULL;
 187                         t->t_wchan = NULL;
 188                         t->t_wchan0 = NULL;
 189                         /*
 190                          * Change thread to transition state and
 191                          * drop the semaphore sleep queue lock.
 192                          */
 193                         THREAD_TRANSITION(t);
 194                         CL_SETRUN(t);
 195                         return;
 196                 }
 197                 tpp = &tp->t_link;
 198         }
 199 }
 200
 201 /*
 202  * operations to perform when changing the priority
 203  * of a thread asleep on a semaphore.
 204  * Called via SOBJ_CHANGE_PRI() and SOBJ_CHANGE_EPRI().
 205  */
 206 static void
 207 sema_change_pri(kthread_t *t, pri_t pri, pri_t *t_prip)
 208 {
 209         ksema_t *sp;
 210
 211         if ((sp = (ksema_t *)t->t_wchan) != NULL) {
 212                 sema_dequeue(sp, t);
 213                 *t_prip = pri;
 214                 sema_queue(sp, t);
 215         } else
 216                 panic("sema_change_pri: %p not on sleep queue", (void *)t);
 217 }
 218
 219 /*
 220  * the semaphore is granted when the semaphore's
 221  * count is greater than zero and blocks when equal
 222  * to zero.
 223  */
 224 void
 225 sema_p(ksema_t *sp)
 226 {
 227         sema_impl_t     *s;
 228         disp_lock_t     *sqlp;
 229
 230         s = (sema_impl_t *)sp;
 231         sqlp = &SQHASH(s)->sq_lock;
 232         disp_lock_enter(sqlp);
 233         ASSERT(s->s_count >= 0);
 234         while (s->s_count == 0) {
 235                 if (panicstr) {
 236                         disp_lock_exit(sqlp);
 237                         return;
 238                 }
 239                 thread_lock_high(curthread);
 240                 SEMA_BLOCK(s, sqlp);
 241                 thread_unlock_nopreempt(curthread);
 242                 swtch();
 243                 disp_lock_enter(sqlp);
 244         }
 245         s->s_count--;
 246         disp_lock_exit(sqlp);
 247 }
 248
 249 /*
 250  * similiar to sema_p except that it blocks at an interruptible
 251  * priority. if a signal is present then return 1 otherwise 0.
 252  */
 253 int
 254 sema_p_sig(ksema_t *sp)
 255 {
 256         kthread_t       *t = curthread;
 257         klwp_t          *lwp = ttolwp(t);
 258         int             cancel_pending;
 259         int             cancelled = 0;
 260         sema_impl_t     *s;
 261         disp_lock_t     *sqlp;
 262
 263         if (lwp == NULL) {
 264                 sema_p(sp);
 265                 return (0);
 266         }
 267
 268         cancel_pending = schedctl_cancel_pending();
 269         s = (sema_impl_t *)sp;
 270         sqlp = &SQHASH(s)->sq_lock;
 271         disp_lock_enter(sqlp);
 272         ASSERT(s->s_count >= 0);
 273         while (s->s_count == 0) {
 274                 proc_t *p = ttoproc(t);
 275                 thread_lock_high(t);
 276                 t->t_flag |= T_WAKEABLE;
 277                 SEMA_BLOCK(s, sqlp);
 278                 lwp->lwp_asleep = 1;
 279                 lwp->lwp_sysabort = 0;
 280                 thread_unlock_nopreempt(t);
 281                 if (ISSIG(t, JUSTLOOKING) || MUSTRETURN(p, t) || cancel_pending)
 282                         setrun(t);
 283                 swtch();
 284                 t->t_flag &= ~T_WAKEABLE;
 285                 if (ISSIG(t, FORREAL) || lwp->lwp_sysabort ||
 286                     MUSTRETURN(p, t) || (cancelled = cancel_pending) != 0) {
 287                         kthread_t *sq, *tp;
 288                         lwp->lwp_asleep = 0;
 289                         lwp->lwp_sysabort = 0;
 290                         disp_lock_enter(sqlp);
 291                         sq = s->s_slpq;
 292                         /*
 293                          * in case sema_v and interrupt happen
 294                          * at the same time, we need to pass the
 295                          * sema_v to the next thread.
 296                          */
 297                         if ((sq != NULL) && (s->s_count > 0)) {
 298                                 tp = sq;
 299                                 ASSERT(THREAD_LOCK_HELD(tp));
 300                                 sq = sq->t_link;
 301                                 tp->t_link = NULL;
 302                                 DTRACE_SCHED1(wakeup, kthread_t *, tp);
 303                                 tp->t_sobj_ops = NULL;
 304                                 tp->t_wchan = NULL;
 305                                 ASSERT(tp->t_state == TS_SLEEP);
 306                                 CL_WAKEUP(tp);
 307                                 s->s_slpq = sq;
 308                                 disp_lock_exit_high(sqlp);
 309                                 thread_unlock(tp);
 310                         } else {
 311                                 disp_lock_exit(sqlp);
 312                         }
 313                         if (cancelled)
 314                                 schedctl_cancel_eintr();
 315                         return (1);
 316                 }
 317                 lwp->lwp_asleep = 0;
 318                 disp_lock_enter(sqlp);
 319         }
 320         s->s_count--;
 321         disp_lock_exit(sqlp);
 322         return (0);
 323 }
 324
 325 /*
 326  * the semaphore's count is incremented by one. a blocked thread
 327  * is awakened and re-tries to acquire the semaphore.
 328  */
 329 void
 330 sema_v(ksema_t *sp)
 331 {
 332         sema_impl_t     *s;
 333         kthread_t       *sq, *tp;
 334         disp_lock_t     *sqlp;
 335
 336         s = (sema_impl_t *)sp;
 337         sqlp = &SQHASH(s)->sq_lock;
 338         disp_lock_enter(sqlp);
 339         if (panicstr) {
 340                 disp_lock_exit(sqlp);
 341                 return;
 342         }
 343         s->s_count++;
 344         sq = s->s_slpq;
 345         if (sq != NULL) {
 346                 tp = sq;
 347                 ASSERT(THREAD_LOCK_HELD(tp));
 348                 sq = sq->t_link;
 349                 tp->t_link = NULL;
 350                 DTRACE_SCHED1(wakeup, kthread_t *, tp);
 351                 tp->t_sobj_ops = NULL;
 352                 tp->t_wchan = NULL;
 353                 ASSERT(tp->t_state == TS_SLEEP);
 354                 CL_WAKEUP(tp);
 355                 s->s_slpq = sq;
 356                 disp_lock_exit_high(sqlp);
 357                 thread_unlock(tp);
 358         } else {
 359                 disp_lock_exit(sqlp);
 360         }
 361 }
 362
 363 /*
 364  * try to acquire the semaphore. if the semaphore is greater than
 365  * zero, then the semaphore is granted and returns 1. otherwise
 366  * return 0.
 367  */
 368 int
 369 sema_tryp(ksema_t *sp)
 370 {
 371         sema_impl_t     *s;
 372         sleepq_head_t   *sqh;
 373
 374         int     gotit = 0;
 375
 376         s = (sema_impl_t *)sp;
 377         sqh = SQHASH(s);
 378         disp_lock_enter(&sqh->sq_lock);
 379         if (s->s_count > 0) {
 380                 s->s_count--;
 381                 gotit = 1;
 382         }
 383         disp_lock_exit(&sqh->sq_lock);
 384         return (gotit);
 385 }
 386
 387 int
 388 sema_held(ksema_t *sp)
 389 {
 390         sema_impl_t     *s;
 391
 392
 393         s = (sema_impl_t *)sp;
 394         if (panicstr)
 395                 return (1);
 396         else
 397                 return (s->s_count <= 0);
 398 }