1 /* 2 * Copyright (c) 2003,2004,2009 The DragonFly Project. All rights reserved. 3 * 4 * This code is derived from software contributed to The DragonFly Project 5 * by Matthew Dillon <dillon@backplane.com> 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 * 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in 15 * the documentation and/or other materials provided with the 16 * distribution. 17 * 3. Neither the name of The DragonFly Project nor the names of its 18 * contributors may be used to endorse or promote products derived 19 * from this software without specific, prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 /* 36 * lwkt_token - Implement soft token locks. 37 * 38 * Tokens are locks which serialize a thread only while the thread is 39 * running. If the thread blocks all tokens are released, then reacquired 40 * when the thread resumes. 41 * 42 * This implementation requires no critical sections or spin locks, but 43 * does use atomic_cmpset_ptr(). 44 * 45 * Tokens may be recursively acquired by the same thread. However the 46 * caller must be sure to release such tokens in reverse order. 47 */ 48 #include <sys/param.h> 49 #include <sys/systm.h> 50 #include <sys/kernel.h> 51 #include <sys/proc.h> 52 #include <sys/rtprio.h> 53 #include <sys/queue.h> 54 #include <sys/sysctl.h> 55 #include <sys/ktr.h> 56 #include <sys/kthread.h> 57 #include <machine/cpu.h> 58 #include <sys/lock.h> 59 #include <sys/caps.h> 60 #include <sys/spinlock.h> 61 62 #include <sys/thread2.h> 63 #include <sys/spinlock2.h> 64 #include <sys/mplock2.h> 65 66 #include <vm/vm.h> 67 #include <vm/vm_param.h> 68 #include <vm/vm_kern.h> 69 #include <vm/vm_object.h> 70 #include <vm/vm_page.h> 71 #include <vm/vm_map.h> 72 #include <vm/vm_pager.h> 73 #include <vm/vm_extern.h> 74 #include <vm/vm_zone.h> 75 76 #include <machine/stdarg.h> 77 #include <machine/smp.h> 78 79 extern int lwkt_sched_debug; 80 81 #ifndef LWKT_NUM_POOL_TOKENS 82 #define LWKT_NUM_POOL_TOKENS 4001 /* prime number */ 83 #endif 84 85 static lwkt_token pool_tokens[LWKT_NUM_POOL_TOKENS]; 86 87 #define TOKEN_STRING "REF=%p TOK=%p TD=%p" 88 #define TOKEN_ARGS lwkt_tokref_t ref, lwkt_token_t tok, struct thread *td 89 #define CONTENDED_STRING TOKEN_STRING " (contention started)" 90 #define UNCONTENDED_STRING TOKEN_STRING " (contention stopped)" 91 #if !defined(KTR_TOKENS) 92 #define KTR_TOKENS KTR_ALL 93 #endif 94 95 KTR_INFO_MASTER(tokens); 96 KTR_INFO(KTR_TOKENS, tokens, fail, 0, TOKEN_STRING, TOKEN_ARGS); 97 KTR_INFO(KTR_TOKENS, tokens, succ, 1, TOKEN_STRING, TOKEN_ARGS); 98 #if 0 99 KTR_INFO(KTR_TOKENS, tokens, release, 2, TOKEN_STRING, TOKEN_ARGS); 100 KTR_INFO(KTR_TOKENS, tokens, remote, 3, TOKEN_STRING, TOKEN_ARGS); 101 KTR_INFO(KTR_TOKENS, tokens, reqremote, 4, TOKEN_STRING, TOKEN_ARGS); 102 KTR_INFO(KTR_TOKENS, tokens, reqfail, 5, TOKEN_STRING, TOKEN_ARGS); 103 KTR_INFO(KTR_TOKENS, tokens, drain, 6, TOKEN_STRING, TOKEN_ARGS); 104 KTR_INFO(KTR_TOKENS, tokens, contention_start, 7, CONTENDED_STRING, TOKEN_ARGS); 105 KTR_INFO(KTR_TOKENS, tokens, contention_stop, 7, UNCONTENDED_STRING, TOKEN_ARGS); 106 #endif 107 108 #define logtoken(name, ref) \ 109 KTR_LOG(tokens_ ## name, ref, ref->tr_tok, curthread) 110 111 /* 112 * Global tokens. These replace the MP lock for major subsystem locking. 113 * These tokens are initially used to lockup both global and individual 114 * operations. 115 * 116 * Once individual structures get their own locks these tokens are used 117 * only to protect global lists & other variables and to interlock 118 * allocations and teardowns and such. 119 * 120 * The UP initializer causes token acquisition to also acquire the MP lock 121 * for maximum compatibility. The feature may be enabled and disabled at 122 * any time, the MP state is copied to the tokref when the token is acquired 123 * and will not race against sysctl changes. 124 */ 125 struct lwkt_token mp_token = LWKT_TOKEN_INITIALIZER(mp_token); 126 struct lwkt_token pmap_token = LWKT_TOKEN_INITIALIZER(pmap_token); 127 struct lwkt_token dev_token = LWKT_TOKEN_INITIALIZER(dev_token); 128 struct lwkt_token vm_token = LWKT_TOKEN_INITIALIZER(vm_token); 129 struct lwkt_token vmspace_token = LWKT_TOKEN_INITIALIZER(vmspace_token); 130 struct lwkt_token kvm_token = LWKT_TOKEN_INITIALIZER(kvm_token); 131 struct lwkt_token proc_token = LWKT_TOKEN_INITIALIZER(proc_token); 132 struct lwkt_token tty_token = LWKT_TOKEN_INITIALIZER(tty_token); 133 struct lwkt_token vnode_token = LWKT_TOKEN_INITIALIZER(vnode_token); 134 struct lwkt_token vmobj_token = LWKT_TOKEN_INITIALIZER(vmobj_token); 135 136 static int lwkt_token_spin = 5; 137 SYSCTL_INT(_lwkt, OID_AUTO, token_spin, CTLFLAG_RW, 138 &lwkt_token_spin, 0, "Decontention spin loops"); 139 static int lwkt_token_delay = 0; 140 SYSCTL_INT(_lwkt, OID_AUTO, token_delay, CTLFLAG_RW, 141 &lwkt_token_delay, 0, "Decontention spin delay in ns"); 142 143 /* 144 * The collision count is bumped every time the LWKT scheduler fails 145 * to acquire needed tokens in addition to a normal lwkt_gettoken() 146 * stall. 147 */ 148 SYSCTL_LONG(_lwkt, OID_AUTO, mp_collisions, CTLFLAG_RW, 149 &mp_token.t_collisions, 0, "Collision counter of mp_token"); 150 SYSCTL_LONG(_lwkt, OID_AUTO, pmap_collisions, CTLFLAG_RW, 151 &pmap_token.t_collisions, 0, "Collision counter of pmap_token"); 152 SYSCTL_LONG(_lwkt, OID_AUTO, dev_collisions, CTLFLAG_RW, 153 &dev_token.t_collisions, 0, "Collision counter of dev_token"); 154 SYSCTL_LONG(_lwkt, OID_AUTO, vm_collisions, CTLFLAG_RW, 155 &vm_token.t_collisions, 0, "Collision counter of vm_token"); 156 SYSCTL_LONG(_lwkt, OID_AUTO, vmspace_collisions, CTLFLAG_RW, 157 &vmspace_token.t_collisions, 0, "Collision counter of vmspace_token"); 158 SYSCTL_LONG(_lwkt, OID_AUTO, kvm_collisions, CTLFLAG_RW, 159 &kvm_token.t_collisions, 0, "Collision counter of kvm_token"); 160 SYSCTL_LONG(_lwkt, OID_AUTO, proc_collisions, CTLFLAG_RW, 161 &proc_token.t_collisions, 0, "Collision counter of proc_token"); 162 SYSCTL_LONG(_lwkt, OID_AUTO, tty_collisions, CTLFLAG_RW, 163 &tty_token.t_collisions, 0, "Collision counter of tty_token"); 164 SYSCTL_LONG(_lwkt, OID_AUTO, vnode_collisions, CTLFLAG_RW, 165 &vnode_token.t_collisions, 0, "Collision counter of vnode_token"); 166 167 #ifdef DEBUG_LOCKS_LATENCY 168 169 static long tokens_add_latency; 170 SYSCTL_LONG(_debug, OID_AUTO, tokens_add_latency, CTLFLAG_RW, 171 &tokens_add_latency, 0, 172 "Add spinlock latency"); 173 174 #endif 175 176 177 static int _lwkt_getalltokens_sorted(thread_t td); 178 179 #ifdef SMP 180 /* 181 * Acquire the initial mplock 182 * 183 * (low level boot only) 184 */ 185 void 186 cpu_get_initial_mplock(void) 187 { 188 KKASSERT(mp_token.t_ref == NULL); 189 if (lwkt_trytoken(&mp_token) == FALSE) 190 panic("cpu_get_initial_mplock"); 191 } 192 #endif 193 194 /* 195 * Return a pool token given an address. Use a prime number to reduce 196 * overlaps. 197 */ 198 static __inline 199 lwkt_token_t 200 _lwkt_token_pool_lookup(void *ptr) 201 { 202 u_int i; 203 204 i = (u_int)(uintptr_t)ptr % LWKT_NUM_POOL_TOKENS; 205 return(&pool_tokens[i]); 206 } 207 208 /* 209 * Initialize a tokref_t prior to making it visible in the thread's 210 * token array. 211 */ 212 static __inline 213 void 214 _lwkt_tokref_init(lwkt_tokref_t ref, lwkt_token_t tok, thread_t td, long excl) 215 { 216 ref->tr_tok = tok; 217 ref->tr_count = excl; 218 ref->tr_owner = td; 219 } 220 221 /* 222 * Attempt to acquire a shared or exclusive token. Returns TRUE on success, 223 * FALSE on failure. 224 * 225 * If TOK_EXCLUSIVE is set in mode we are attempting to get an exclusive 226 * token, otherwise are attempting to get a shared token. 227 * 228 * If TOK_EXCLREQ is set in mode this is a blocking operation, otherwise 229 * it is a non-blocking operation (for both exclusive or shared acquisions). 230 */ 231 static __inline 232 int 233 _lwkt_trytokref(lwkt_tokref_t ref, thread_t td, long mode) 234 { 235 lwkt_token_t tok; 236 lwkt_tokref_t oref; 237 long count; 238 239 tok = ref->tr_tok; 240 KASSERT(((mode & TOK_EXCLREQ) == 0 || /* non blocking */ 241 td->td_gd->gd_intr_nesting_level == 0 || 242 panic_cpu_gd == mycpu), 243 ("Attempt to acquire token %p not already " 244 "held in hard code section", tok)); 245 246 if (mode & TOK_EXCLUSIVE) { 247 /* 248 * Attempt to get an exclusive token 249 */ 250 for (;;) { 251 count = tok->t_count; 252 oref = tok->t_ref; /* can be NULL */ 253 cpu_ccfence(); 254 if ((count & ~TOK_EXCLREQ) == 0) { 255 /* 256 * It is possible to get the exclusive bit. 257 * We must clear TOK_EXCLREQ on successful 258 * acquisition. 259 */ 260 if (atomic_cmpset_long(&tok->t_count, count, 261 (count & ~TOK_EXCLREQ) | 262 TOK_EXCLUSIVE)) { 263 KKASSERT(tok->t_ref == NULL); 264 tok->t_ref = ref; 265 return TRUE; 266 } 267 /* retry */ 268 } else if ((count & TOK_EXCLUSIVE) && 269 oref >= &td->td_toks_base && 270 oref < td->td_toks_stop) { 271 /* 272 * Our thread already holds the exclusive 273 * bit, we treat this tokref as a shared 274 * token (sorta) to make the token release 275 * code easier. 276 * 277 * NOTE: oref cannot race above if it 278 * happens to be ours, so we're good. 279 * But we must still have a stable 280 * variable for both parts of the 281 * comparison. 282 * 283 * NOTE: Since we already have an exclusive 284 * lock and don't need to check EXCLREQ 285 * we can just use an atomic_add here 286 */ 287 atomic_add_long(&tok->t_count, TOK_INCR); 288 ref->tr_count &= ~TOK_EXCLUSIVE; 289 return TRUE; 290 } else if ((mode & TOK_EXCLREQ) && 291 (count & TOK_EXCLREQ) == 0) { 292 /* 293 * Unable to get the exclusive bit but being 294 * asked to set the exclusive-request bit. 295 * Since we are going to retry anyway just 296 * set the bit unconditionally. 297 */ 298 atomic_set_long(&tok->t_count, TOK_EXCLREQ); 299 return FALSE; 300 } else { 301 /* 302 * Unable to get the exclusive bit and not 303 * being asked to set the exclusive-request 304 * (aka lwkt_trytoken()), or EXCLREQ was 305 * already set. 306 */ 307 cpu_pause(); 308 return FALSE; 309 } 310 /* retry */ 311 } 312 } else { 313 /* 314 * Attempt to get a shared token. Note that TOK_EXCLREQ 315 * for shared tokens simply means the caller intends to 316 * block. We never actually set the bit in tok->t_count. 317 */ 318 for (;;) { 319 count = tok->t_count; 320 oref = tok->t_ref; /* can be NULL */ 321 cpu_ccfence(); 322 if ((count & (TOK_EXCLUSIVE/*|TOK_EXCLREQ*/)) == 0) { 323 /* XXX EXCLREQ should work */ 324 /* 325 * It is possible to get the token shared. 326 */ 327 if (atomic_cmpset_long(&tok->t_count, count, 328 count + TOK_INCR)) { 329 return TRUE; 330 } 331 /* retry */ 332 } else if ((count & TOK_EXCLUSIVE) && 333 oref >= &td->td_toks_base && 334 oref < td->td_toks_stop) { 335 /* 336 * We own the exclusive bit on the token so 337 * we can in fact also get it shared. 338 */ 339 atomic_add_long(&tok->t_count, TOK_INCR); 340 return TRUE; 341 } else { 342 /* 343 * We failed to get the token shared 344 */ 345 return FALSE; 346 } 347 /* retry */ 348 } 349 } 350 } 351 352 static __inline 353 int 354 _lwkt_trytokref_spin(lwkt_tokref_t ref, thread_t td, long mode) 355 { 356 int spin; 357 358 if (_lwkt_trytokref(ref, td, mode)) { 359 #ifdef DEBUG_LOCKS_LATENCY 360 long j; 361 for (j = tokens_add_latency; j > 0; --j) 362 cpu_ccfence(); 363 #endif 364 return TRUE; 365 } 366 for (spin = lwkt_token_spin; spin > 0; --spin) { 367 if (lwkt_token_delay) 368 tsc_delay(lwkt_token_delay); 369 else 370 cpu_pause(); 371 if (_lwkt_trytokref(ref, td, mode)) { 372 #ifdef DEBUG_LOCKS_LATENCY 373 long j; 374 for (j = tokens_add_latency; j > 0; --j) 375 cpu_ccfence(); 376 #endif 377 return TRUE; 378 } 379 } 380 return FALSE; 381 } 382 383 /* 384 * Release a token that we hold. 385 */ 386 static __inline 387 void 388 _lwkt_reltokref(lwkt_tokref_t ref, thread_t td) 389 { 390 lwkt_token_t tok; 391 long count; 392 393 tok = ref->tr_tok; 394 for (;;) { 395 count = tok->t_count; 396 cpu_ccfence(); 397 if (tok->t_ref == ref) { 398 /* 399 * We are an exclusive holder. We must clear tr_ref 400 * before we clear the TOK_EXCLUSIVE bit. If we are 401 * unable to clear the bit we must restore 402 * tok->t_ref. 403 */ 404 KKASSERT(count & TOK_EXCLUSIVE); 405 tok->t_ref = NULL; 406 if (atomic_cmpset_long(&tok->t_count, count, 407 count & ~TOK_EXCLUSIVE)) { 408 return; 409 } 410 tok->t_ref = ref; 411 /* retry */ 412 } else { 413 /* 414 * We are a shared holder 415 */ 416 KKASSERT(count & TOK_COUNTMASK); 417 if (atomic_cmpset_long(&tok->t_count, count, 418 count - TOK_INCR)) { 419 return; 420 } 421 /* retry */ 422 } 423 /* retry */ 424 } 425 } 426 427 /* 428 * Obtain all the tokens required by the specified thread on the current 429 * cpu, return 0 on failure and non-zero on success. If a failure occurs 430 * any partially acquired tokens will be released prior to return. 431 * 432 * lwkt_getalltokens is called by the LWKT scheduler to re-acquire all 433 * tokens that the thread had to release when it switched away. 434 * 435 * If spinning is non-zero this function acquires the tokens in a particular 436 * order to deal with potential deadlocks. We simply use address order for 437 * the case. 438 * 439 * Called from a critical section. 440 */ 441 int 442 lwkt_getalltokens(thread_t td, int spinning) 443 { 444 lwkt_tokref_t scan; 445 lwkt_token_t tok; 446 447 if (spinning) 448 return(_lwkt_getalltokens_sorted(td)); 449 450 /* 451 * Acquire tokens in forward order, assign or validate tok->t_ref. 452 */ 453 for (scan = &td->td_toks_base; scan < td->td_toks_stop; ++scan) { 454 tok = scan->tr_tok; 455 for (;;) { 456 /* 457 * Only try really hard on the last token 458 */ 459 if (scan == td->td_toks_stop - 1) { 460 if (_lwkt_trytokref_spin(scan, td, scan->tr_count)) 461 break; 462 } else { 463 if (_lwkt_trytokref(scan, td, scan->tr_count)) 464 break; 465 } 466 467 /* 468 * Otherwise we failed to acquire all the tokens. 469 * Release whatever we did get. 470 */ 471 if (lwkt_sched_debug > 0) { 472 --lwkt_sched_debug; 473 kprintf("toka %p %s %s\n", 474 tok, tok->t_desc, td->td_comm); 475 } 476 td->td_wmesg = tok->t_desc; 477 ++tok->t_collisions; 478 while (--scan >= &td->td_toks_base) 479 _lwkt_reltokref(scan, td); 480 return(FALSE); 481 } 482 } 483 return (TRUE); 484 } 485 486 /* 487 * Release all tokens owned by the specified thread on the current cpu. 488 * 489 * This code is really simple. Even in cases where we own all the tokens 490 * note that t_ref may not match the scan for recursively held tokens which 491 * are held deeper in the stack, or for the case where a lwkt_getalltokens() 492 * failed. 493 * 494 * Tokens are released in reverse order to reduce chasing race failures. 495 * 496 * Called from a critical section. 497 */ 498 void 499 lwkt_relalltokens(thread_t td) 500 { 501 lwkt_tokref_t scan; 502 503 /* 504 * Weird order is to try to avoid a panic loop 505 */ 506 if (td->td_toks_have) { 507 scan = td->td_toks_have; 508 td->td_toks_have = NULL; 509 } else { 510 scan = td->td_toks_stop; 511 } 512 while (--scan >= &td->td_toks_base) 513 _lwkt_reltokref(scan, td); 514 } 515 516 /* 517 * This is the decontention version of lwkt_getalltokens(). The tokens are 518 * acquired in address-sorted order to deal with any deadlocks. Ultimately 519 * token failures will spin into the scheduler and get here. 520 * 521 * Called from critical section 522 */ 523 static 524 int 525 _lwkt_getalltokens_sorted(thread_t td) 526 { 527 lwkt_tokref_t sort_array[LWKT_MAXTOKENS]; 528 lwkt_tokref_t scan; 529 lwkt_token_t tok; 530 int i; 531 int j; 532 int n; 533 534 /* 535 * Sort the token array. Yah yah, I know this isn't fun. 536 * 537 * NOTE: Recursively acquired tokens are ordered the same as in the 538 * td_toks_array so we can always get the earliest one first. 539 */ 540 i = 0; 541 scan = &td->td_toks_base; 542 while (scan < td->td_toks_stop) { 543 for (j = 0; j < i; ++j) { 544 if (scan->tr_tok < sort_array[j]->tr_tok) 545 break; 546 } 547 if (j != i) { 548 bcopy(sort_array + j, sort_array + j + 1, 549 (i - j) * sizeof(lwkt_tokref_t)); 550 } 551 sort_array[j] = scan; 552 ++scan; 553 ++i; 554 } 555 n = i; 556 557 /* 558 * Acquire tokens in forward order, assign or validate tok->t_ref. 559 */ 560 for (i = 0; i < n; ++i) { 561 scan = sort_array[i]; 562 tok = scan->tr_tok; 563 for (;;) { 564 /* 565 * Only try really hard on the last token 566 */ 567 if (scan == td->td_toks_stop - 1) { 568 if (_lwkt_trytokref_spin(scan, td, scan->tr_count)) 569 break; 570 } else { 571 if (_lwkt_trytokref(scan, td, scan->tr_count)) 572 break; 573 } 574 575 /* 576 * Otherwise we failed to acquire all the tokens. 577 * Release whatever we did get. 578 */ 579 if (lwkt_sched_debug > 0) { 580 --lwkt_sched_debug; 581 kprintf("tokb %p %s %s\n", 582 tok, tok->t_desc, td->td_comm); 583 } 584 td->td_wmesg = tok->t_desc; 585 ++tok->t_collisions; 586 while (--i >= 0) { 587 scan = sort_array[i]; 588 _lwkt_reltokref(scan, td); 589 } 590 return(FALSE); 591 } 592 } 593 594 /* 595 * We were successful, there is no need for another core to signal 596 * us. 597 */ 598 return (TRUE); 599 } 600 601 /* 602 * Get a serializing token. This routine can block. 603 */ 604 void 605 lwkt_gettoken(lwkt_token_t tok) 606 { 607 thread_t td = curthread; 608 lwkt_tokref_t ref; 609 610 ref = td->td_toks_stop; 611 KKASSERT(ref < &td->td_toks_end); 612 ++td->td_toks_stop; 613 cpu_ccfence(); 614 _lwkt_tokref_init(ref, tok, td, TOK_EXCLUSIVE|TOK_EXCLREQ); 615 616 #ifdef DEBUG_LOCKS 617 /* 618 * Taking an exclusive token after holding it shared will 619 * livelock. Scan for that case and assert. 620 */ 621 lwkt_tokref_t tk; 622 int found = 0; 623 for (tk = &td->td_toks_base; tk < ref; tk++) { 624 if (tk->tr_tok != tok) 625 continue; 626 627 found++; 628 if (tk->tr_count & TOK_EXCLUSIVE) 629 goto good; 630 } 631 /* We found only shared instances of this token if found >0 here */ 632 KASSERT((found == 0), ("Token %p s/x livelock", tok)); 633 good: 634 #endif 635 636 if (_lwkt_trytokref_spin(ref, td, TOK_EXCLUSIVE|TOK_EXCLREQ)) 637 return; 638 639 /* 640 * Give up running if we can't acquire the token right now. 641 * 642 * Since the tokref is already active the scheduler now 643 * takes care of acquisition, so we need only call 644 * lwkt_switch(). 645 * 646 * Since we failed this was not a recursive token so upon 647 * return tr_tok->t_ref should be assigned to this specific 648 * ref. 649 */ 650 td->td_wmesg = tok->t_desc; 651 ++tok->t_collisions; 652 logtoken(fail, ref); 653 td->td_toks_have = td->td_toks_stop - 1; 654 lwkt_switch(); 655 logtoken(succ, ref); 656 KKASSERT(tok->t_ref == ref); 657 } 658 659 /* 660 * Similar to gettoken but we acquire a shared token instead of an exclusive 661 * token. 662 */ 663 void 664 lwkt_gettoken_shared(lwkt_token_t tok) 665 { 666 thread_t td = curthread; 667 lwkt_tokref_t ref; 668 669 ref = td->td_toks_stop; 670 KKASSERT(ref < &td->td_toks_end); 671 ++td->td_toks_stop; 672 cpu_ccfence(); 673 _lwkt_tokref_init(ref, tok, td, TOK_EXCLREQ); 674 675 #ifdef DEBUG_LOCKS 676 /* 677 * Taking a pool token in shared mode is a bad idea; other 678 * addresses deeper in the call stack may hash to the same pool 679 * token and you may end up with an exclusive-shared livelock. 680 * Warn in this condition. 681 */ 682 if ((tok >= &pool_tokens[0]) && 683 (tok < &pool_tokens[LWKT_NUM_POOL_TOKENS])) 684 kprintf("Warning! Taking pool token %p in shared mode\n", tok); 685 #endif 686 687 688 if (_lwkt_trytokref_spin(ref, td, TOK_EXCLREQ)) 689 return; 690 691 /* 692 * Give up running if we can't acquire the token right now. 693 * 694 * Since the tokref is already active the scheduler now 695 * takes care of acquisition, so we need only call 696 * lwkt_switch(). 697 * 698 * Since we failed this was not a recursive token so upon 699 * return tr_tok->t_ref should be assigned to this specific 700 * ref. 701 */ 702 td->td_wmesg = tok->t_desc; 703 ++tok->t_collisions; 704 logtoken(fail, ref); 705 td->td_toks_have = td->td_toks_stop - 1; 706 lwkt_switch(); 707 logtoken(succ, ref); 708 } 709 710 /* 711 * Attempt to acquire a token, return TRUE on success, FALSE on failure. 712 * 713 * We setup the tokref in case we actually get the token (if we switch later 714 * it becomes mandatory so we set TOK_EXCLREQ), but we call trytokref without 715 * TOK_EXCLREQ in case we fail. 716 */ 717 int 718 lwkt_trytoken(lwkt_token_t tok) 719 { 720 thread_t td = curthread; 721 lwkt_tokref_t ref; 722 723 ref = td->td_toks_stop; 724 KKASSERT(ref < &td->td_toks_end); 725 ++td->td_toks_stop; 726 cpu_ccfence(); 727 _lwkt_tokref_init(ref, tok, td, TOK_EXCLUSIVE|TOK_EXCLREQ); 728 729 if (_lwkt_trytokref(ref, td, TOK_EXCLUSIVE)) 730 return TRUE; 731 732 /* 733 * Failed, unpend the request 734 */ 735 cpu_ccfence(); 736 --td->td_toks_stop; 737 ++tok->t_collisions; 738 return FALSE; 739 } 740 741 742 void 743 lwkt_gettoken_hard(lwkt_token_t tok) 744 { 745 lwkt_gettoken(tok); 746 crit_enter_hard(); 747 } 748 749 lwkt_token_t 750 lwkt_getpooltoken(void *ptr) 751 { 752 lwkt_token_t tok; 753 754 tok = _lwkt_token_pool_lookup(ptr); 755 lwkt_gettoken(tok); 756 return (tok); 757 } 758 759 /* 760 * Release a serializing token. 761 * 762 * WARNING! All tokens must be released in reverse order. This will be 763 * asserted. 764 */ 765 void 766 lwkt_reltoken(lwkt_token_t tok) 767 { 768 thread_t td = curthread; 769 lwkt_tokref_t ref; 770 771 /* 772 * Remove ref from thread token list and assert that it matches 773 * the token passed in. Tokens must be released in reverse order. 774 */ 775 ref = td->td_toks_stop - 1; 776 KKASSERT(ref >= &td->td_toks_base && ref->tr_tok == tok); 777 _lwkt_reltokref(ref, td); 778 cpu_sfence(); 779 td->td_toks_stop = ref; 780 } 781 782 void 783 lwkt_reltoken_hard(lwkt_token_t tok) 784 { 785 lwkt_reltoken(tok); 786 crit_exit_hard(); 787 } 788 789 /* 790 * It is faster for users of lwkt_getpooltoken() to use the returned 791 * token and just call lwkt_reltoken(), but for convenience we provide 792 * this function which looks the token up based on the ident. 793 */ 794 void 795 lwkt_relpooltoken(void *ptr) 796 { 797 lwkt_token_t tok = _lwkt_token_pool_lookup(ptr); 798 lwkt_reltoken(tok); 799 } 800 801 /* 802 * Return a count of the number of token refs the thread has to the 803 * specified token, whether it currently owns the token or not. 804 */ 805 int 806 lwkt_cnttoken(lwkt_token_t tok, thread_t td) 807 { 808 lwkt_tokref_t scan; 809 int count = 0; 810 811 for (scan = &td->td_toks_base; scan < td->td_toks_stop; ++scan) { 812 if (scan->tr_tok == tok) 813 ++count; 814 } 815 return(count); 816 } 817 818 /* 819 * Pool tokens are used to provide a type-stable serializing token 820 * pointer that does not race against disappearing data structures. 821 * 822 * This routine is called in early boot just after we setup the BSP's 823 * globaldata structure. 824 */ 825 void 826 lwkt_token_pool_init(void) 827 { 828 int i; 829 830 for (i = 0; i < LWKT_NUM_POOL_TOKENS; ++i) 831 lwkt_token_init(&pool_tokens[i], "pool"); 832 } 833 834 lwkt_token_t 835 lwkt_token_pool_lookup(void *ptr) 836 { 837 return (_lwkt_token_pool_lookup(ptr)); 838 } 839 840 /* 841 * Initialize a token. 842 */ 843 void 844 lwkt_token_init(lwkt_token_t tok, const char *desc) 845 { 846 tok->t_count = 0; 847 tok->t_ref = NULL; 848 tok->t_collisions = 0; 849 tok->t_desc = desc; 850 } 851 852 void 853 lwkt_token_uninit(lwkt_token_t tok) 854 { 855 /* empty */ 856 } 857 858 /* 859 * Exchange the two most recent tokens on the tokref stack. This allows 860 * you to release a token out of order. 861 * 862 * We have to be careful about the case where the top two tokens are 863 * the same token. In this case tok->t_ref will point to the deeper 864 * ref and must remain pointing to the deeper ref. If we were to swap 865 * it the first release would clear the token even though a second 866 * ref is still present. 867 * 868 * Only exclusively held tokens contain a reference to the tokref which 869 * has to be flipped along with the swap. 870 */ 871 void 872 lwkt_token_swap(void) 873 { 874 lwkt_tokref_t ref1, ref2; 875 lwkt_token_t tok1, tok2; 876 long count1, count2; 877 thread_t td = curthread; 878 879 crit_enter(); 880 881 ref1 = td->td_toks_stop - 1; 882 ref2 = td->td_toks_stop - 2; 883 KKASSERT(ref1 >= &td->td_toks_base); 884 KKASSERT(ref2 >= &td->td_toks_base); 885 886 tok1 = ref1->tr_tok; 887 tok2 = ref2->tr_tok; 888 count1 = ref1->tr_count; 889 count2 = ref2->tr_count; 890 891 if (tok1 != tok2) { 892 ref1->tr_tok = tok2; 893 ref1->tr_count = count2; 894 ref2->tr_tok = tok1; 895 ref2->tr_count = count1; 896 if (tok1->t_ref == ref1) 897 tok1->t_ref = ref2; 898 if (tok2->t_ref == ref2) 899 tok2->t_ref = ref1; 900 } 901 902 crit_exit(); 903 } 904