1 /* $NetBSD: sys_select.c,v 1.32 2011/05/18 14:48:04 christos Exp $ */ 2 3 /*- 4 * Copyright (c) 2007, 2008, 2009, 2010 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Andrew Doran and Mindaugas Rasiukevicius. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 /* 33 * Copyright (c) 1982, 1986, 1989, 1993 34 * The Regents of the University of California. All rights reserved. 35 * (c) UNIX System Laboratories, Inc. 36 * All or some portions of this file are derived from material licensed 37 * to the University of California by American Telephone and Telegraph 38 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 39 * the permission of UNIX System Laboratories, Inc. 40 * 41 * Redistribution and use in source and binary forms, with or without 42 * modification, are permitted provided that the following conditions 43 * are met: 44 * 1. Redistributions of source code must retain the above copyright 45 * notice, this list of conditions and the following disclaimer. 46 * 2. Redistributions in binary form must reproduce the above copyright 47 * notice, this list of conditions and the following disclaimer in the 48 * documentation and/or other materials provided with the distribution. 49 * 3. Neither the name of the University nor the names of its contributors 50 * may be used to endorse or promote products derived from this software 51 * without specific prior written permission. 52 * 53 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 54 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 55 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 56 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 57 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 58 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 59 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 60 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 61 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 62 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 63 * SUCH DAMAGE. 64 * 65 * @(#)sys_generic.c 8.9 (Berkeley) 2/14/95 66 */ 67 68 /* 69 * System calls of synchronous I/O multiplexing subsystem. 70 * 71 * Locking 72 * 73 * Two locks are used: <object-lock> and selcluster_t::sc_lock. 74 * 75 * The <object-lock> might be a device driver or another subsystem, e.g. 76 * socket or pipe. This lock is not exported, and thus invisible to this 77 * subsystem. Mainly, synchronisation between selrecord() and selnotify() 78 * routines depends on this lock, as it will be described in the comments. 79 * 80 * Lock order 81 * 82 * <object-lock> -> 83 * selcluster_t::sc_lock 84 */ 85 86 #include <sys/cdefs.h> 87 __KERNEL_RCSID(0, "$NetBSD: sys_select.c,v 1.32 2011/05/18 14:48:04 christos Exp $"); 88 89 #include <sys/param.h> 90 #include <sys/systm.h> 91 #include <sys/filedesc.h> 92 #include <sys/file.h> 93 #include <sys/proc.h> 94 #include <sys/socketvar.h> 95 #include <sys/signalvar.h> 96 #include <sys/uio.h> 97 #include <sys/kernel.h> 98 #include <sys/lwp.h> 99 #include <sys/poll.h> 100 #include <sys/mount.h> 101 #include <sys/syscallargs.h> 102 #include <sys/cpu.h> 103 #include <sys/atomic.h> 104 #include <sys/socketvar.h> 105 #include <sys/sleepq.h> 106 107 /* Flags for lwp::l_selflag. */ 108 #define SEL_RESET 0 /* awoken, interrupted, or not yet polling */ 109 #define SEL_SCANNING 1 /* polling descriptors */ 110 #define SEL_BLOCKING 2 /* blocking and waiting for event */ 111 #define SEL_EVENT 3 /* interrupted, events set directly */ 112 113 /* Operations: either select() or poll(). */ 114 #define SELOP_SELECT 1 115 #define SELOP_POLL 2 116 117 /* 118 * Per-cluster state for select()/poll(). For a system with fewer 119 * than 32 CPUs, this gives us per-CPU clusters. 120 */ 121 #define SELCLUSTERS 32 122 #define SELCLUSTERMASK (SELCLUSTERS - 1) 123 124 typedef struct selcluster { 125 kmutex_t *sc_lock; 126 sleepq_t sc_sleepq; 127 int sc_ncoll; 128 uint32_t sc_mask; 129 } selcluster_t; 130 131 static inline int selscan(char *, const int, const size_t, register_t *); 132 static inline int pollscan(struct pollfd *, const int, register_t *); 133 static void selclear(void); 134 135 static const int sel_flag[] = { 136 POLLRDNORM | POLLHUP | POLLERR, 137 POLLWRNORM | POLLHUP | POLLERR, 138 POLLRDBAND 139 }; 140 141 static syncobj_t select_sobj = { 142 SOBJ_SLEEPQ_FIFO, 143 sleepq_unsleep, 144 sleepq_changepri, 145 sleepq_lendpri, 146 syncobj_noowner, 147 }; 148 149 static selcluster_t *selcluster[SELCLUSTERS] __read_mostly; 150 151 /* 152 * Select system call. 153 */ 154 int 155 sys___pselect50(struct lwp *l, const struct sys___pselect50_args *uap, 156 register_t *retval) 157 { 158 /* { 159 syscallarg(int) nd; 160 syscallarg(fd_set *) in; 161 syscallarg(fd_set *) ou; 162 syscallarg(fd_set *) ex; 163 syscallarg(const struct timespec *) ts; 164 syscallarg(sigset_t *) mask; 165 } */ 166 struct timespec ats, *ts = NULL; 167 sigset_t amask, *mask = NULL; 168 int error; 169 170 if (SCARG(uap, ts)) { 171 error = copyin(SCARG(uap, ts), &ats, sizeof(ats)); 172 if (error) 173 return error; 174 ts = &ats; 175 } 176 if (SCARG(uap, mask) != NULL) { 177 error = copyin(SCARG(uap, mask), &amask, sizeof(amask)); 178 if (error) 179 return error; 180 mask = &amask; 181 } 182 183 return selcommon(retval, SCARG(uap, nd), SCARG(uap, in), 184 SCARG(uap, ou), SCARG(uap, ex), ts, mask); 185 } 186 187 int 188 sys___select50(struct lwp *l, const struct sys___select50_args *uap, 189 register_t *retval) 190 { 191 /* { 192 syscallarg(int) nd; 193 syscallarg(fd_set *) in; 194 syscallarg(fd_set *) ou; 195 syscallarg(fd_set *) ex; 196 syscallarg(struct timeval *) tv; 197 } */ 198 struct timeval atv; 199 struct timespec ats, *ts = NULL; 200 int error; 201 202 if (SCARG(uap, tv)) { 203 error = copyin(SCARG(uap, tv), (void *)&atv, sizeof(atv)); 204 if (error) 205 return error; 206 TIMEVAL_TO_TIMESPEC(&atv, &ats); 207 ts = &ats; 208 } 209 210 return selcommon(retval, SCARG(uap, nd), SCARG(uap, in), 211 SCARG(uap, ou), SCARG(uap, ex), ts, NULL); 212 } 213 214 /* 215 * sel_do_scan: common code to perform the scan on descriptors. 216 */ 217 static int 218 sel_do_scan(const int op, void *fds, const int nf, const size_t ni, 219 struct timespec *ts, sigset_t *mask, register_t *retval) 220 { 221 lwp_t * const l = curlwp; 222 selcluster_t *sc; 223 kmutex_t *lock; 224 struct timespec sleepts; 225 int error, timo; 226 227 timo = 0; 228 if (ts && inittimeleft(ts, &sleepts) == -1) { 229 return EINVAL; 230 } 231 232 if (__predict_false(mask)) 233 sigsuspendsetup(l, mask); 234 235 sc = curcpu()->ci_data.cpu_selcluster; 236 lock = sc->sc_lock; 237 l->l_selcluster = sc; 238 SLIST_INIT(&l->l_selwait); 239 240 l->l_selret = 0; 241 if (op == SELOP_SELECT) { 242 l->l_selbits = fds; 243 l->l_selni = ni; 244 } else { 245 l->l_selbits = NULL; 246 } 247 for (;;) { 248 int ncoll; 249 250 /* 251 * No need to lock. If this is overwritten by another value 252 * while scanning, we will retry below. We only need to see 253 * exact state from the descriptors that we are about to poll, 254 * and lock activity resulting from fo_poll is enough to 255 * provide an up to date value for new polling activity. 256 */ 257 l->l_selflag = SEL_SCANNING; 258 ncoll = sc->sc_ncoll; 259 260 if (op == SELOP_SELECT) { 261 error = selscan((char *)fds, nf, ni, retval); 262 } else { 263 error = pollscan((struct pollfd *)fds, nf, retval); 264 } 265 if (error || *retval) 266 break; 267 if (ts && (timo = gettimeleft(ts, &sleepts)) <= 0) 268 break; 269 /* 270 * Acquire the lock and perform the (re)checks. Note, if 271 * collision has occured, then our state does not matter, 272 * as we must perform re-scan. Therefore, check it first. 273 */ 274 state_check: 275 mutex_spin_enter(lock); 276 if (__predict_false(sc->sc_ncoll != ncoll)) { 277 /* Collision: perform re-scan. */ 278 mutex_spin_exit(lock); 279 continue; 280 } 281 if (__predict_true(l->l_selflag == SEL_EVENT)) { 282 /* Events occured, they are set directly. */ 283 mutex_spin_exit(lock); 284 KASSERT(l->l_selret != 0); 285 *retval = l->l_selret; 286 break; 287 } 288 if (__predict_true(l->l_selflag == SEL_RESET)) { 289 /* Events occured, but re-scan is requested. */ 290 mutex_spin_exit(lock); 291 continue; 292 } 293 /* Nothing happen, therefore - sleep. */ 294 l->l_selflag = SEL_BLOCKING; 295 l->l_kpriority = true; 296 sleepq_enter(&sc->sc_sleepq, l, lock); 297 sleepq_enqueue(&sc->sc_sleepq, sc, "select", &select_sobj); 298 error = sleepq_block(timo, true); 299 if (error != 0) { 300 break; 301 } 302 /* Awoken: need to check the state. */ 303 goto state_check; 304 } 305 selclear(); 306 307 /* select and poll are not restarted after signals... */ 308 if (error == ERESTART) 309 return EINTR; 310 if (error == EWOULDBLOCK) 311 return 0; 312 return error; 313 } 314 315 int 316 selcommon(register_t *retval, int nd, fd_set *u_in, fd_set *u_ou, 317 fd_set *u_ex, struct timespec *ts, sigset_t *mask) 318 { 319 char smallbits[howmany(FD_SETSIZE, NFDBITS) * 320 sizeof(fd_mask) * 6]; 321 char *bits; 322 int error, nf; 323 size_t ni; 324 325 if (nd < 0) 326 return (EINVAL); 327 nf = curlwp->l_fd->fd_dt->dt_nfiles; 328 if (nd > nf) { 329 /* forgiving; slightly wrong */ 330 nd = nf; 331 } 332 ni = howmany(nd, NFDBITS) * sizeof(fd_mask); 333 if (ni * 6 > sizeof(smallbits)) { 334 bits = kmem_alloc(ni * 6, KM_SLEEP); 335 if (bits == NULL) 336 return ENOMEM; 337 } else 338 bits = smallbits; 339 340 #define getbits(name, x) \ 341 if (u_ ## name) { \ 342 error = copyin(u_ ## name, bits + ni * x, ni); \ 343 if (error) \ 344 goto fail; \ 345 } else \ 346 memset(bits + ni * x, 0, ni); 347 getbits(in, 0); 348 getbits(ou, 1); 349 getbits(ex, 2); 350 #undef getbits 351 352 error = sel_do_scan(SELOP_SELECT, bits, nd, ni, ts, mask, retval); 353 if (error == 0 && u_in != NULL) 354 error = copyout(bits + ni * 3, u_in, ni); 355 if (error == 0 && u_ou != NULL) 356 error = copyout(bits + ni * 4, u_ou, ni); 357 if (error == 0 && u_ex != NULL) 358 error = copyout(bits + ni * 5, u_ex, ni); 359 fail: 360 if (bits != smallbits) 361 kmem_free(bits, ni * 6); 362 return (error); 363 } 364 365 static inline int 366 selscan(char *bits, const int nfd, const size_t ni, register_t *retval) 367 { 368 fd_mask *ibitp, *obitp; 369 int msk, i, j, fd, n; 370 file_t *fp; 371 372 ibitp = (fd_mask *)(bits + ni * 0); 373 obitp = (fd_mask *)(bits + ni * 3); 374 n = 0; 375 376 for (msk = 0; msk < 3; msk++) { 377 for (i = 0; i < nfd; i += NFDBITS) { 378 fd_mask ibits, obits; 379 380 ibits = *ibitp++; 381 obits = 0; 382 while ((j = ffs(ibits)) && (fd = i + --j) < nfd) { 383 ibits &= ~(1 << j); 384 if ((fp = fd_getfile(fd)) == NULL) 385 return (EBADF); 386 /* 387 * Setup an argument to selrecord(), which is 388 * a file descriptor number. 389 */ 390 curlwp->l_selrec = fd; 391 if ((*fp->f_ops->fo_poll)(fp, sel_flag[msk])) { 392 obits |= (1 << j); 393 n++; 394 } 395 fd_putfile(fd); 396 } 397 *obitp++ = obits; 398 } 399 } 400 *retval = n; 401 return (0); 402 } 403 404 /* 405 * Poll system call. 406 */ 407 int 408 sys_poll(struct lwp *l, const struct sys_poll_args *uap, register_t *retval) 409 { 410 /* { 411 syscallarg(struct pollfd *) fds; 412 syscallarg(u_int) nfds; 413 syscallarg(int) timeout; 414 } */ 415 struct timespec ats, *ts = NULL; 416 417 if (SCARG(uap, timeout) != INFTIM) { 418 ats.tv_sec = SCARG(uap, timeout) / 1000; 419 ats.tv_nsec = (SCARG(uap, timeout) % 1000) * 1000000; 420 ts = &ats; 421 } 422 423 return pollcommon(retval, SCARG(uap, fds), SCARG(uap, nfds), ts, NULL); 424 } 425 426 /* 427 * Poll system call. 428 */ 429 int 430 sys___pollts50(struct lwp *l, const struct sys___pollts50_args *uap, 431 register_t *retval) 432 { 433 /* { 434 syscallarg(struct pollfd *) fds; 435 syscallarg(u_int) nfds; 436 syscallarg(const struct timespec *) ts; 437 syscallarg(const sigset_t *) mask; 438 } */ 439 struct timespec ats, *ts = NULL; 440 sigset_t amask, *mask = NULL; 441 int error; 442 443 if (SCARG(uap, ts)) { 444 error = copyin(SCARG(uap, ts), &ats, sizeof(ats)); 445 if (error) 446 return error; 447 ts = &ats; 448 } 449 if (SCARG(uap, mask)) { 450 error = copyin(SCARG(uap, mask), &amask, sizeof(amask)); 451 if (error) 452 return error; 453 mask = &amask; 454 } 455 456 return pollcommon(retval, SCARG(uap, fds), SCARG(uap, nfds), ts, mask); 457 } 458 459 int 460 pollcommon(register_t *retval, struct pollfd *u_fds, u_int nfds, 461 struct timespec *ts, sigset_t *mask) 462 { 463 struct pollfd smallfds[32]; 464 struct pollfd *fds; 465 int error; 466 size_t ni; 467 468 if (nfds > 1000 + curlwp->l_fd->fd_dt->dt_nfiles) { 469 /* 470 * Either the user passed in a very sparse 'fds' or junk! 471 * The kmem_alloc() call below would be bad news. 472 * We could process the 'fds' array in chunks, but that 473 * is a lot of code that isn't normally useful. 474 * (Or just move the copyin/out into pollscan().) 475 * Historically the code silently truncated 'fds' to 476 * dt_nfiles entries - but that does cause issues. 477 */ 478 return EINVAL; 479 } 480 ni = nfds * sizeof(struct pollfd); 481 if (ni > sizeof(smallfds)) { 482 fds = kmem_alloc(ni, KM_SLEEP); 483 if (fds == NULL) 484 return ENOMEM; 485 } else 486 fds = smallfds; 487 488 error = copyin(u_fds, fds, ni); 489 if (error) 490 goto fail; 491 492 error = sel_do_scan(SELOP_POLL, fds, nfds, ni, ts, mask, retval); 493 if (error == 0) 494 error = copyout(fds, u_fds, ni); 495 fail: 496 if (fds != smallfds) 497 kmem_free(fds, ni); 498 return (error); 499 } 500 501 static inline int 502 pollscan(struct pollfd *fds, const int nfd, register_t *retval) 503 { 504 file_t *fp; 505 int i, n = 0; 506 507 for (i = 0; i < nfd; i++, fds++) { 508 if (fds->fd < 0) { 509 fds->revents = 0; 510 } else if ((fp = fd_getfile(fds->fd)) == NULL) { 511 fds->revents = POLLNVAL; 512 n++; 513 } else { 514 /* 515 * Perform poll: registers select request or returns 516 * the events which are set. Setup an argument for 517 * selrecord(), which is a pointer to struct pollfd. 518 */ 519 curlwp->l_selrec = (uintptr_t)fds; 520 fds->revents = (*fp->f_ops->fo_poll)(fp, 521 fds->events | POLLERR | POLLHUP); 522 if (fds->revents != 0) 523 n++; 524 fd_putfile(fds->fd); 525 } 526 } 527 *retval = n; 528 return (0); 529 } 530 531 int 532 seltrue(dev_t dev, int events, lwp_t *l) 533 { 534 535 return (events & (POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM)); 536 } 537 538 /* 539 * Record a select request. Concurrency issues: 540 * 541 * The caller holds the same lock across calls to selrecord() and 542 * selnotify(), so we don't need to consider a concurrent wakeup 543 * while in this routine. 544 * 545 * The only activity we need to guard against is selclear(), called by 546 * another thread that is exiting sel_do_scan(). 547 * `sel_lwp' can only become non-NULL while the caller's lock is held, 548 * so it cannot become non-NULL due to a change made by another thread 549 * while we are in this routine. It can only become _NULL_ due to a 550 * call to selclear(). 551 * 552 * If it is non-NULL and != selector there is the potential for 553 * selclear() to be called by another thread. If either of those 554 * conditions are true, we're not interested in touching the `named 555 * waiter' part of the selinfo record because we need to record a 556 * collision. Hence there is no need for additional locking in this 557 * routine. 558 */ 559 void 560 selrecord(lwp_t *selector, struct selinfo *sip) 561 { 562 selcluster_t *sc; 563 lwp_t *other; 564 565 KASSERT(selector == curlwp); 566 567 sc = selector->l_selcluster; 568 other = sip->sel_lwp; 569 570 if (other == selector) { 571 /* 1. We (selector) already claimed to be the first LWP. */ 572 KASSERT(sip->sel_cluster = sc); 573 } else if (other == NULL) { 574 /* 575 * 2. No first LWP, therefore we (selector) are the first. 576 * 577 * There may be unnamed waiters (collisions). Issue a memory 578 * barrier to ensure that we access sel_lwp (above) before 579 * other fields - this guards against a call to selclear(). 580 */ 581 membar_enter(); 582 sip->sel_lwp = selector; 583 SLIST_INSERT_HEAD(&selector->l_selwait, sip, sel_chain); 584 /* Copy the argument, which is for selnotify(). */ 585 sip->sel_fdinfo = selector->l_selrec; 586 /* Replace selinfo's lock with the chosen cluster's lock. */ 587 sip->sel_cluster = sc; 588 } else { 589 /* 3. Multiple waiters: record a collision. */ 590 sip->sel_collision |= sc->sc_mask; 591 KASSERT(sip->sel_cluster != NULL); 592 } 593 } 594 595 /* 596 * sel_setevents: a helper function for selnotify(), to set the events 597 * for LWP sleeping in selcommon() or pollcommon(). 598 */ 599 static inline bool 600 sel_setevents(lwp_t *l, struct selinfo *sip, const int events) 601 { 602 const int oflag = l->l_selflag; 603 int ret = 0; 604 605 /* 606 * If we require re-scan or it was required by somebody else, 607 * then just (re)set SEL_RESET and return. 608 */ 609 if (__predict_false(events == 0 || oflag == SEL_RESET)) { 610 l->l_selflag = SEL_RESET; 611 return true; 612 } 613 /* 614 * Direct set. Note: select state of LWP is locked. First, 615 * determine whether it is selcommon() or pollcommon(). 616 */ 617 if (l->l_selbits != NULL) { 618 const size_t ni = l->l_selni; 619 fd_mask *fds = (fd_mask *)l->l_selbits; 620 fd_mask *ofds = (fd_mask *)((char *)fds + ni * 3); 621 const int fd = sip->sel_fdinfo, fbit = 1 << (fd & __NFDMASK); 622 const int idx = fd >> __NFDSHIFT; 623 int n; 624 625 for (n = 0; n < 3; n++) { 626 if ((fds[idx] & fbit) != 0 && (sel_flag[n] & events)) { 627 ofds[idx] |= fbit; 628 ret++; 629 } 630 fds = (fd_mask *)((char *)fds + ni); 631 ofds = (fd_mask *)((char *)ofds + ni); 632 } 633 } else { 634 struct pollfd *pfd = (void *)sip->sel_fdinfo; 635 int revents = events & (pfd->events | POLLERR | POLLHUP); 636 637 if (revents) { 638 pfd->revents |= revents; 639 ret = 1; 640 } 641 } 642 /* Check whether there are any events to return. */ 643 if (!ret) { 644 return false; 645 } 646 /* Indicate direct set and note the event (cluster lock is held). */ 647 l->l_selflag = SEL_EVENT; 648 l->l_selret += ret; 649 return true; 650 } 651 652 /* 653 * Do a wakeup when a selectable event occurs. Concurrency issues: 654 * 655 * As per selrecord(), the caller's object lock is held. If there 656 * is a named waiter, we must acquire the associated selcluster's lock 657 * in order to synchronize with selclear() and pollers going to sleep 658 * in sel_do_scan(). 659 * 660 * sip->sel_cluser cannot change at this point, as it is only changed 661 * in selrecord(), and concurrent calls to selrecord() are locked 662 * out by the caller. 663 */ 664 void 665 selnotify(struct selinfo *sip, int events, long knhint) 666 { 667 selcluster_t *sc; 668 uint32_t mask; 669 int index, oflag; 670 lwp_t *l; 671 kmutex_t *lock; 672 673 KNOTE(&sip->sel_klist, knhint); 674 675 if (sip->sel_lwp != NULL) { 676 /* One named LWP is waiting. */ 677 sc = sip->sel_cluster; 678 lock = sc->sc_lock; 679 mutex_spin_enter(lock); 680 /* Still there? */ 681 if (sip->sel_lwp != NULL) { 682 /* 683 * Set the events for our LWP and indicate that. 684 * Otherwise, request for a full re-scan. 685 */ 686 l = sip->sel_lwp; 687 oflag = l->l_selflag; 688 #ifndef NO_DIRECT_SELECT 689 if (!sel_setevents(l, sip, events)) { 690 /* No events to return. */ 691 mutex_spin_exit(lock); 692 return; 693 } 694 #else 695 l->l_selflag = SEL_RESET; 696 #endif 697 /* 698 * If thread is sleeping, wake it up. If it's not 699 * yet asleep, it will notice the change in state 700 * and will re-poll the descriptors. 701 */ 702 if (oflag == SEL_BLOCKING && l->l_mutex == lock) { 703 KASSERT(l->l_wchan == sc); 704 sleepq_unsleep(l, false); 705 } 706 } 707 mutex_spin_exit(lock); 708 } 709 710 if ((mask = sip->sel_collision) != 0) { 711 /* 712 * There was a collision (multiple waiters): we must 713 * inform all potentially interested waiters. 714 */ 715 sip->sel_collision = 0; 716 do { 717 index = ffs(mask) - 1; 718 mask &= ~(1 << index); 719 sc = selcluster[index]; 720 lock = sc->sc_lock; 721 mutex_spin_enter(lock); 722 sc->sc_ncoll++; 723 sleepq_wake(&sc->sc_sleepq, sc, (u_int)-1, lock); 724 } while (__predict_false(mask != 0)); 725 } 726 } 727 728 /* 729 * Remove an LWP from all objects that it is waiting for. Concurrency 730 * issues: 731 * 732 * The object owner's (e.g. device driver) lock is not held here. Calls 733 * can be made to selrecord() and we do not synchronize against those 734 * directly using locks. However, we use `sel_lwp' to lock out changes. 735 * Before clearing it we must use memory barriers to ensure that we can 736 * safely traverse the list of selinfo records. 737 */ 738 static void 739 selclear(void) 740 { 741 struct selinfo *sip, *next; 742 selcluster_t *sc; 743 lwp_t *l; 744 kmutex_t *lock; 745 746 l = curlwp; 747 sc = l->l_selcluster; 748 lock = sc->sc_lock; 749 750 mutex_spin_enter(lock); 751 for (sip = SLIST_FIRST(&l->l_selwait); sip != NULL; sip = next) { 752 KASSERT(sip->sel_lwp == l); 753 KASSERT(sip->sel_cluster == l->l_selcluster); 754 755 /* 756 * Read link to next selinfo record, if any. 757 * It's no longer safe to touch `sip' after clearing 758 * `sel_lwp', so ensure that the read of `sel_chain' 759 * completes before the clearing of sel_lwp becomes 760 * globally visible. 761 */ 762 next = SLIST_NEXT(sip, sel_chain); 763 membar_exit(); 764 /* Release the record for another named waiter to use. */ 765 sip->sel_lwp = NULL; 766 } 767 mutex_spin_exit(lock); 768 } 769 770 /* 771 * Initialize the select/poll system calls. Called once for each 772 * CPU in the system, as they are attached. 773 */ 774 void 775 selsysinit(struct cpu_info *ci) 776 { 777 selcluster_t *sc; 778 u_int index; 779 780 /* If already a cluster in place for this bit, re-use. */ 781 index = cpu_index(ci) & SELCLUSTERMASK; 782 sc = selcluster[index]; 783 if (sc == NULL) { 784 sc = kmem_alloc(roundup2(sizeof(selcluster_t), 785 coherency_unit) + coherency_unit, KM_SLEEP); 786 sc = (void *)roundup2((uintptr_t)sc, coherency_unit); 787 sc->sc_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_SCHED); 788 sleepq_init(&sc->sc_sleepq); 789 sc->sc_ncoll = 0; 790 sc->sc_mask = (1 << index); 791 selcluster[index] = sc; 792 } 793 ci->ci_data.cpu_selcluster = sc; 794 } 795 796 /* 797 * Initialize a selinfo record. 798 */ 799 void 800 selinit(struct selinfo *sip) 801 { 802 803 memset(sip, 0, sizeof(*sip)); 804 } 805 806 /* 807 * Destroy a selinfo record. The owning object must not gain new 808 * references while this is in progress: all activity on the record 809 * must be stopped. 810 * 811 * Concurrency issues: we only need guard against a call to selclear() 812 * by a thread exiting sel_do_scan(). The caller has prevented further 813 * references being made to the selinfo record via selrecord(), and it 814 * will not call selnotify() again. 815 */ 816 void 817 seldestroy(struct selinfo *sip) 818 { 819 selcluster_t *sc; 820 kmutex_t *lock; 821 lwp_t *l; 822 823 if (sip->sel_lwp == NULL) 824 return; 825 826 /* 827 * Lock out selclear(). The selcluster pointer can't change while 828 * we are here since it is only ever changed in selrecord(), 829 * and that will not be entered again for this record because 830 * it is dying. 831 */ 832 KASSERT(sip->sel_cluster != NULL); 833 sc = sip->sel_cluster; 834 lock = sc->sc_lock; 835 mutex_spin_enter(lock); 836 if ((l = sip->sel_lwp) != NULL) { 837 /* 838 * This should rarely happen, so although SLIST_REMOVE() 839 * is slow, using it here is not a problem. 840 */ 841 KASSERT(l->l_selcluster == sc); 842 SLIST_REMOVE(&l->l_selwait, sip, selinfo, sel_chain); 843 sip->sel_lwp = NULL; 844 } 845 mutex_spin_exit(lock); 846 } 847 848 int 849 pollsock(struct socket *so, const struct timespec *tsp, int events) 850 { 851 int ncoll, error, timo; 852 struct timespec sleepts, ts; 853 selcluster_t *sc; 854 lwp_t *l; 855 kmutex_t *lock; 856 857 timo = 0; 858 if (tsp != NULL) { 859 ts = *tsp; 860 if (inittimeleft(&ts, &sleepts) == -1) 861 return EINVAL; 862 } 863 864 l = curlwp; 865 sc = curcpu()->ci_data.cpu_selcluster; 866 lock = sc->sc_lock; 867 l->l_selcluster = sc; 868 SLIST_INIT(&l->l_selwait); 869 error = 0; 870 for (;;) { 871 /* 872 * No need to lock. If this is overwritten by another 873 * value while scanning, we will retry below. We only 874 * need to see exact state from the descriptors that 875 * we are about to poll, and lock activity resulting 876 * from fo_poll is enough to provide an up to date value 877 * for new polling activity. 878 */ 879 ncoll = sc->sc_ncoll; 880 l->l_selflag = SEL_SCANNING; 881 if (sopoll(so, events) != 0) 882 break; 883 if (tsp && (timo = gettimeleft(&ts, &sleepts)) <= 0) 884 break; 885 mutex_spin_enter(lock); 886 if (l->l_selflag != SEL_SCANNING || sc->sc_ncoll != ncoll) { 887 mutex_spin_exit(lock); 888 continue; 889 } 890 l->l_selflag = SEL_BLOCKING; 891 sleepq_enter(&sc->sc_sleepq, l, lock); 892 sleepq_enqueue(&sc->sc_sleepq, sc, "pollsock", &select_sobj); 893 error = sleepq_block(timo, true); 894 if (error != 0) 895 break; 896 } 897 selclear(); 898 /* poll is not restarted after signals... */ 899 if (error == ERESTART) 900 error = EINTR; 901 if (error == EWOULDBLOCK) 902 error = 0; 903 return (error); 904 } 905