FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_mutex.c
1 /*-
2 * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 * 3. Berkeley Software Design Inc's name may not be used to endorse or
13 * promote products derived from this software without specific prior
14 * written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``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 BERKELEY SOFTWARE DESIGN INC 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 * from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
29 * and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
30 * $FreeBSD: releng/5.0/sys/kern/kern_mutex.c 105919 2002-10-25 08:40:20Z phk $
31 */
32
33 /*
34 * Machine independent bits of mutex implementation.
35 */
36
37 #include "opt_adaptive_mutexes.h"
38 #include "opt_ddb.h"
39
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/bus.h>
43 #include <sys/kernel.h>
44 #include <sys/ktr.h>
45 #include <sys/lock.h>
46 #include <sys/malloc.h>
47 #include <sys/mutex.h>
48 #include <sys/proc.h>
49 #include <sys/resourcevar.h>
50 #include <sys/sched.h>
51 #include <sys/sbuf.h>
52 #include <sys/stdint.h>
53 #include <sys/sysctl.h>
54 #include <sys/vmmeter.h>
55
56 #include <machine/atomic.h>
57 #include <machine/bus.h>
58 #include <machine/clock.h>
59 #include <machine/cpu.h>
60
61 #include <ddb/ddb.h>
62
63 #include <vm/vm.h>
64 #include <vm/vm_extern.h>
65
66 /*
67 * Internal utility macros.
68 */
69 #define mtx_unowned(m) ((m)->mtx_lock == MTX_UNOWNED)
70
71 #define mtx_owner(m) (mtx_unowned((m)) ? NULL \
72 : (struct thread *)((m)->mtx_lock & MTX_FLAGMASK))
73
74 /* XXXKSE This test will change. */
75 #define thread_running(td) \
76 ((td)->td_kse != NULL && (td)->td_kse->ke_oncpu != NOCPU)
77
78 /*
79 * Lock classes for sleep and spin mutexes.
80 */
81 struct lock_class lock_class_mtx_sleep = {
82 "sleep mutex",
83 LC_SLEEPLOCK | LC_RECURSABLE
84 };
85 struct lock_class lock_class_mtx_spin = {
86 "spin mutex",
87 LC_SPINLOCK | LC_RECURSABLE
88 };
89
90 /*
91 * System-wide mutexes
92 */
93 struct mtx sched_lock;
94 struct mtx Giant;
95
96 /*
97 * Prototypes for non-exported routines.
98 */
99 static void propagate_priority(struct thread *);
100
101 static void
102 propagate_priority(struct thread *td)
103 {
104 int pri = td->td_priority;
105 struct mtx *m = td->td_blocked;
106
107 mtx_assert(&sched_lock, MA_OWNED);
108 for (;;) {
109 struct thread *td1;
110
111 td = mtx_owner(m);
112
113 if (td == NULL) {
114 /*
115 * This really isn't quite right. Really
116 * ought to bump priority of thread that
117 * next acquires the mutex.
118 */
119 MPASS(m->mtx_lock == MTX_CONTESTED);
120 return;
121 }
122
123 MPASS(td->td_proc != NULL);
124 MPASS(td->td_proc->p_magic == P_MAGIC);
125 KASSERT(!TD_IS_SLEEPING(td), ("sleeping thread owns a mutex"));
126 if (td->td_priority <= pri) /* lower is higher priority */
127 return;
128
129
130 /*
131 * If lock holder is actually running, just bump priority.
132 */
133 if (TD_IS_RUNNING(td)) {
134 td->td_priority = pri;
135 return;
136 }
137
138 #ifndef SMP
139 /*
140 * For UP, we check to see if td is curthread (this shouldn't
141 * ever happen however as it would mean we are in a deadlock.)
142 */
143 KASSERT(td != curthread, ("Deadlock detected"));
144 #endif
145
146 /*
147 * If on run queue move to new run queue, and quit.
148 * XXXKSE this gets a lot more complicated under threads
149 * but try anyhow.
150 */
151 if (TD_ON_RUNQ(td)) {
152 MPASS(td->td_blocked == NULL);
153 sched_prio(td, pri);
154 return;
155 }
156 /*
157 * Adjust for any other cases.
158 */
159 td->td_priority = pri;
160
161 /*
162 * If we aren't blocked on a mutex, we should be.
163 */
164 KASSERT(TD_ON_LOCK(td), (
165 "process %d(%s):%d holds %s but isn't blocked on a mutex\n",
166 td->td_proc->p_pid, td->td_proc->p_comm, td->td_state,
167 m->mtx_object.lo_name));
168
169 /*
170 * Pick up the mutex that td is blocked on.
171 */
172 m = td->td_blocked;
173 MPASS(m != NULL);
174
175 /*
176 * Check if the thread needs to be moved up on
177 * the blocked chain
178 */
179 if (td == TAILQ_FIRST(&m->mtx_blocked)) {
180 continue;
181 }
182
183 td1 = TAILQ_PREV(td, threadqueue, td_lockq);
184 if (td1->td_priority <= pri) {
185 continue;
186 }
187
188 /*
189 * Remove thread from blocked chain and determine where
190 * it should be moved up to. Since we know that td1 has
191 * a lower priority than td, we know that at least one
192 * thread in the chain has a lower priority and that
193 * td1 will thus not be NULL after the loop.
194 */
195 TAILQ_REMOVE(&m->mtx_blocked, td, td_lockq);
196 TAILQ_FOREACH(td1, &m->mtx_blocked, td_lockq) {
197 MPASS(td1->td_proc->p_magic == P_MAGIC);
198 if (td1->td_priority > pri)
199 break;
200 }
201
202 MPASS(td1 != NULL);
203 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
204 CTR4(KTR_LOCK,
205 "propagate_priority: p %p moved before %p on [%p] %s",
206 td, td1, m, m->mtx_object.lo_name);
207 }
208 }
209
210 #ifdef MUTEX_PROFILING
211 SYSCTL_NODE(_debug, OID_AUTO, mutex, CTLFLAG_RD, NULL, "mutex debugging");
212 SYSCTL_NODE(_debug_mutex, OID_AUTO, prof, CTLFLAG_RD, NULL, "mutex profiling");
213 static int mutex_prof_enable = 0;
214 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, enable, CTLFLAG_RW,
215 &mutex_prof_enable, 0, "Enable tracing of mutex holdtime");
216
217 struct mutex_prof {
218 const char *name;
219 const char *file;
220 int line;
221 struct {
222 uintmax_t max;
223 uintmax_t tot;
224 uintmax_t cur;
225 } cnt;
226 struct mutex_prof *next;
227 };
228
229 /*
230 * mprof_buf is a static pool of profiling records to avoid possible
231 * reentrance of the memory allocation functions.
232 *
233 * Note: NUM_MPROF_BUFFERS must be smaller than MPROF_HASH_SIZE.
234 */
235 #define NUM_MPROF_BUFFERS 1000
236 static struct mutex_prof mprof_buf[NUM_MPROF_BUFFERS];
237 static int first_free_mprof_buf;
238 #define MPROF_HASH_SIZE 1009
239 static struct mutex_prof *mprof_hash[MPROF_HASH_SIZE];
240
241 static int mutex_prof_acquisitions;
242 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, acquisitions, CTLFLAG_RD,
243 &mutex_prof_acquisitions, 0, "Number of mutex acquistions recorded");
244 static int mutex_prof_records;
245 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, records, CTLFLAG_RD,
246 &mutex_prof_records, 0, "Number of profiling records");
247 static int mutex_prof_maxrecords = NUM_MPROF_BUFFERS;
248 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, maxrecords, CTLFLAG_RD,
249 &mutex_prof_maxrecords, 0, "Maximum number of profiling records");
250 static int mutex_prof_rejected;
251 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, rejected, CTLFLAG_RD,
252 &mutex_prof_rejected, 0, "Number of rejected profiling records");
253 static int mutex_prof_hashsize = MPROF_HASH_SIZE;
254 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, hashsize, CTLFLAG_RD,
255 &mutex_prof_hashsize, 0, "Hash size");
256 static int mutex_prof_collisions = 0;
257 SYSCTL_INT(_debug_mutex_prof, OID_AUTO, collisions, CTLFLAG_RD,
258 &mutex_prof_collisions, 0, "Number of hash collisions");
259
260 /*
261 * mprof_mtx protects the profiling buffers and the hash.
262 */
263 static struct mtx mprof_mtx;
264 MTX_SYSINIT(mprof, &mprof_mtx, "mutex profiling lock", MTX_SPIN | MTX_QUIET);
265
266 static u_int64_t
267 nanoseconds(void)
268 {
269 struct timespec tv;
270
271 nanotime(&tv);
272 return (tv.tv_sec * (u_int64_t)1000000000 + tv.tv_nsec);
273 }
274
275 static int
276 dump_mutex_prof_stats(SYSCTL_HANDLER_ARGS)
277 {
278 struct sbuf *sb;
279 int error, i;
280
281 if (first_free_mprof_buf == 0)
282 return (SYSCTL_OUT(req, "No locking recorded",
283 sizeof("No locking recorded")));
284
285 sb = sbuf_new(NULL, NULL, 1024, SBUF_AUTOEXTEND);
286 sbuf_printf(sb, "%6s %12s %11s %5s %s\n",
287 "max", "total", "count", "avg", "name");
288 /*
289 * XXX this spinlock seems to be by far the largest perpetrator
290 * of spinlock latency (1.6 msec on an Athlon1600 was recorded
291 * even before I pessimized it further by moving the average
292 * computation here).
293 */
294 mtx_lock_spin(&mprof_mtx);
295 for (i = 0; i < first_free_mprof_buf; ++i)
296 sbuf_printf(sb, "%6ju %12ju %11ju %5ju %s:%d (%s)\n",
297 mprof_buf[i].cnt.max / 1000,
298 mprof_buf[i].cnt.tot / 1000,
299 mprof_buf[i].cnt.cur,
300 mprof_buf[i].cnt.cur == 0 ? (uintmax_t)0 :
301 mprof_buf[i].cnt.tot / (mprof_buf[i].cnt.cur * 1000),
302 mprof_buf[i].file, mprof_buf[i].line, mprof_buf[i].name);
303 mtx_unlock_spin(&mprof_mtx);
304 sbuf_finish(sb);
305 error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1);
306 sbuf_delete(sb);
307 return (error);
308 }
309 SYSCTL_PROC(_debug_mutex_prof, OID_AUTO, stats, CTLTYPE_STRING | CTLFLAG_RD,
310 NULL, 0, dump_mutex_prof_stats, "A", "Mutex profiling statistics");
311 #endif
312
313 /*
314 * Function versions of the inlined __mtx_* macros. These are used by
315 * modules and can also be called from assembly language if needed.
316 */
317 void
318 _mtx_lock_flags(struct mtx *m, int opts, const char *file, int line)
319 {
320
321 MPASS(curthread != NULL);
322 KASSERT(m->mtx_object.lo_class == &lock_class_mtx_sleep,
323 ("mtx_lock() of spin mutex %s @ %s:%d", m->mtx_object.lo_name,
324 file, line));
325 _get_sleep_lock(m, curthread, opts, file, line);
326 LOCK_LOG_LOCK("LOCK", &m->mtx_object, opts, m->mtx_recurse, file,
327 line);
328 WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
329 #ifdef MUTEX_PROFILING
330 /* don't reset the timer when/if recursing */
331 if (m->mtx_acqtime == 0) {
332 m->mtx_filename = file;
333 m->mtx_lineno = line;
334 m->mtx_acqtime = mutex_prof_enable ? nanoseconds() : 0;
335 ++mutex_prof_acquisitions;
336 }
337 #endif
338 }
339
340 void
341 _mtx_unlock_flags(struct mtx *m, int opts, const char *file, int line)
342 {
343
344 MPASS(curthread != NULL);
345 KASSERT(m->mtx_object.lo_class == &lock_class_mtx_sleep,
346 ("mtx_unlock() of spin mutex %s @ %s:%d", m->mtx_object.lo_name,
347 file, line));
348 WITNESS_UNLOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
349 LOCK_LOG_LOCK("UNLOCK", &m->mtx_object, opts, m->mtx_recurse, file,
350 line);
351 mtx_assert(m, MA_OWNED);
352 #ifdef MUTEX_PROFILING
353 if (m->mtx_acqtime != 0) {
354 static const char *unknown = "(unknown)";
355 struct mutex_prof *mpp;
356 u_int64_t acqtime, now;
357 const char *p, *q;
358 volatile u_int hash;
359
360 now = nanoseconds();
361 acqtime = m->mtx_acqtime;
362 m->mtx_acqtime = 0;
363 if (now <= acqtime)
364 goto out;
365 for (p = m->mtx_filename; strncmp(p, "../", 3) == 0; p += 3)
366 /* nothing */ ;
367 if (p == NULL || *p == '\0')
368 p = unknown;
369 for (hash = m->mtx_lineno, q = p; *q != '\0'; ++q)
370 hash = (hash * 2 + *q) % MPROF_HASH_SIZE;
371 mtx_lock_spin(&mprof_mtx);
372 for (mpp = mprof_hash[hash]; mpp != NULL; mpp = mpp->next)
373 if (mpp->line == m->mtx_lineno &&
374 strcmp(mpp->file, p) == 0)
375 break;
376 if (mpp == NULL) {
377 /* Just exit if we cannot get a trace buffer */
378 if (first_free_mprof_buf >= NUM_MPROF_BUFFERS) {
379 ++mutex_prof_rejected;
380 goto unlock;
381 }
382 mpp = &mprof_buf[first_free_mprof_buf++];
383 mpp->name = mtx_name(m);
384 mpp->file = p;
385 mpp->line = m->mtx_lineno;
386 mpp->next = mprof_hash[hash];
387 if (mprof_hash[hash] != NULL)
388 ++mutex_prof_collisions;
389 mprof_hash[hash] = mpp;
390 ++mutex_prof_records;
391 }
392 /*
393 * Record if the mutex has been held longer now than ever
394 * before.
395 */
396 if (now - acqtime > mpp->cnt.max)
397 mpp->cnt.max = now - acqtime;
398 mpp->cnt.tot += now - acqtime;
399 mpp->cnt.cur++;
400 unlock:
401 mtx_unlock_spin(&mprof_mtx);
402 }
403 out:
404 #endif
405 _rel_sleep_lock(m, curthread, opts, file, line);
406 }
407
408 void
409 _mtx_lock_spin_flags(struct mtx *m, int opts, const char *file, int line)
410 {
411
412 MPASS(curthread != NULL);
413 KASSERT(m->mtx_object.lo_class == &lock_class_mtx_spin,
414 ("mtx_lock_spin() of sleep mutex %s @ %s:%d",
415 m->mtx_object.lo_name, file, line));
416 #if defined(SMP) || LOCK_DEBUG > 0 || 1
417 _get_spin_lock(m, curthread, opts, file, line);
418 #else
419 critical_enter();
420 #endif
421 LOCK_LOG_LOCK("LOCK", &m->mtx_object, opts, m->mtx_recurse, file,
422 line);
423 WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
424 }
425
426 void
427 _mtx_unlock_spin_flags(struct mtx *m, int opts, const char *file, int line)
428 {
429
430 MPASS(curthread != NULL);
431 KASSERT(m->mtx_object.lo_class == &lock_class_mtx_spin,
432 ("mtx_unlock_spin() of sleep mutex %s @ %s:%d",
433 m->mtx_object.lo_name, file, line));
434 WITNESS_UNLOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
435 LOCK_LOG_LOCK("UNLOCK", &m->mtx_object, opts, m->mtx_recurse, file,
436 line);
437 mtx_assert(m, MA_OWNED);
438 #if defined(SMP) || LOCK_DEBUG > 0 || 1
439 _rel_spin_lock(m);
440 #else
441 critical_exit();
442 #endif
443 }
444
445 /*
446 * The important part of mtx_trylock{,_flags}()
447 * Tries to acquire lock `m.' We do NOT handle recursion here; we assume that
448 * if we're called, it's because we know we don't already own this lock.
449 */
450 int
451 _mtx_trylock(struct mtx *m, int opts, const char *file, int line)
452 {
453 int rval;
454
455 MPASS(curthread != NULL);
456
457 rval = _obtain_lock(m, curthread);
458
459 LOCK_LOG_TRY("LOCK", &m->mtx_object, opts, rval, file, line);
460 if (rval) {
461 /*
462 * We do not handle recursion in _mtx_trylock; see the
463 * note at the top of the routine.
464 */
465 KASSERT(!mtx_recursed(m),
466 ("mtx_trylock() called on a recursed mutex"));
467 WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE | LOP_TRYLOCK,
468 file, line);
469 }
470
471 return (rval);
472 }
473
474 /*
475 * _mtx_lock_sleep: the tougher part of acquiring an MTX_DEF lock.
476 *
477 * We call this if the lock is either contested (i.e. we need to go to
478 * sleep waiting for it), or if we need to recurse on it.
479 */
480 void
481 _mtx_lock_sleep(struct mtx *m, int opts, const char *file, int line)
482 {
483 struct thread *td = curthread;
484 #if defined(SMP) && defined(ADAPTIVE_MUTEXES)
485 struct thread *owner;
486 #endif
487 #ifdef KTR
488 int cont_logged = 0;
489 #endif
490
491 if ((m->mtx_lock & MTX_FLAGMASK) == (uintptr_t)td) {
492 m->mtx_recurse++;
493 atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
494 if (LOCK_LOG_TEST(&m->mtx_object, opts))
495 CTR1(KTR_LOCK, "_mtx_lock_sleep: %p recursing", m);
496 return;
497 }
498
499 if (LOCK_LOG_TEST(&m->mtx_object, opts))
500 CTR4(KTR_LOCK,
501 "_mtx_lock_sleep: %s contested (lock=%p) at %s:%d",
502 m->mtx_object.lo_name, (void *)m->mtx_lock, file, line);
503
504 while (!_obtain_lock(m, td)) {
505 uintptr_t v;
506 struct thread *td1;
507
508 mtx_lock_spin(&sched_lock);
509 /*
510 * Check if the lock has been released while spinning for
511 * the sched_lock.
512 */
513 if ((v = m->mtx_lock) == MTX_UNOWNED) {
514 mtx_unlock_spin(&sched_lock);
515 #ifdef __i386__
516 ia32_pause();
517 #endif
518 continue;
519 }
520
521 /*
522 * The mutex was marked contested on release. This means that
523 * there are threads blocked on it.
524 */
525 if (v == MTX_CONTESTED) {
526 td1 = TAILQ_FIRST(&m->mtx_blocked);
527 MPASS(td1 != NULL);
528 m->mtx_lock = (uintptr_t)td | MTX_CONTESTED;
529
530 if (td1->td_priority < td->td_priority)
531 td->td_priority = td1->td_priority;
532 mtx_unlock_spin(&sched_lock);
533 return;
534 }
535
536 /*
537 * If the mutex isn't already contested and a failure occurs
538 * setting the contested bit, the mutex was either released
539 * or the state of the MTX_RECURSED bit changed.
540 */
541 if ((v & MTX_CONTESTED) == 0 &&
542 !atomic_cmpset_ptr(&m->mtx_lock, (void *)v,
543 (void *)(v | MTX_CONTESTED))) {
544 mtx_unlock_spin(&sched_lock);
545 #ifdef __i386__
546 ia32_pause();
547 #endif
548 continue;
549 }
550
551 #if defined(SMP) && defined(ADAPTIVE_MUTEXES)
552 /*
553 * If the current owner of the lock is executing on another
554 * CPU, spin instead of blocking.
555 */
556 owner = (struct thread *)(v & MTX_FLAGMASK);
557 if (m != &Giant && thread_running(owner)) {
558 mtx_unlock_spin(&sched_lock);
559 while (mtx_owner(m) == owner && thread_running(owner)) {
560 #ifdef __i386__
561 ia32_pause();
562 #endif
563 }
564 continue;
565 }
566 #endif /* SMP && ADAPTIVE_MUTEXES */
567
568 /*
569 * We definitely must sleep for this lock.
570 */
571 mtx_assert(m, MA_NOTOWNED);
572
573 #ifdef notyet
574 /*
575 * If we're borrowing an interrupted thread's VM context, we
576 * must clean up before going to sleep.
577 */
578 if (td->td_ithd != NULL) {
579 struct ithd *it = td->td_ithd;
580
581 if (it->it_interrupted) {
582 if (LOCK_LOG_TEST(&m->mtx_object, opts))
583 CTR2(KTR_LOCK,
584 "_mtx_lock_sleep: %p interrupted %p",
585 it, it->it_interrupted);
586 intr_thd_fixup(it);
587 }
588 }
589 #endif
590
591 /*
592 * Put us on the list of threads blocked on this mutex.
593 */
594 if (TAILQ_EMPTY(&m->mtx_blocked)) {
595 td1 = mtx_owner(m);
596 LIST_INSERT_HEAD(&td1->td_contested, m, mtx_contested);
597 TAILQ_INSERT_TAIL(&m->mtx_blocked, td, td_lockq);
598 } else {
599 TAILQ_FOREACH(td1, &m->mtx_blocked, td_lockq)
600 if (td1->td_priority > td->td_priority)
601 break;
602 if (td1)
603 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
604 else
605 TAILQ_INSERT_TAIL(&m->mtx_blocked, td, td_lockq);
606 }
607 #ifdef KTR
608 if (!cont_logged) {
609 CTR6(KTR_CONTENTION,
610 "contention: %p at %s:%d wants %s, taken by %s:%d",
611 td, file, line, m->mtx_object.lo_name,
612 WITNESS_FILE(&m->mtx_object),
613 WITNESS_LINE(&m->mtx_object));
614 cont_logged = 1;
615 }
616 #endif
617
618 /*
619 * Save who we're blocked on.
620 */
621 td->td_blocked = m;
622 td->td_lockname = m->mtx_object.lo_name;
623 TD_SET_LOCK(td);
624 propagate_priority(td);
625
626 if (LOCK_LOG_TEST(&m->mtx_object, opts))
627 CTR3(KTR_LOCK,
628 "_mtx_lock_sleep: p %p blocked on [%p] %s", td, m,
629 m->mtx_object.lo_name);
630
631 td->td_proc->p_stats->p_ru.ru_nvcsw++;
632 mi_switch();
633
634 if (LOCK_LOG_TEST(&m->mtx_object, opts))
635 CTR3(KTR_LOCK,
636 "_mtx_lock_sleep: p %p free from blocked on [%p] %s",
637 td, m, m->mtx_object.lo_name);
638
639 mtx_unlock_spin(&sched_lock);
640 }
641
642 #ifdef KTR
643 if (cont_logged) {
644 CTR4(KTR_CONTENTION,
645 "contention end: %s acquired by %p at %s:%d",
646 m->mtx_object.lo_name, td, file, line);
647 }
648 #endif
649 return;
650 }
651
652 /*
653 * _mtx_lock_spin: the tougher part of acquiring an MTX_SPIN lock.
654 *
655 * This is only called if we need to actually spin for the lock. Recursion
656 * is handled inline.
657 */
658 void
659 _mtx_lock_spin(struct mtx *m, int opts, const char *file, int line)
660 {
661 int i = 0;
662
663 if (LOCK_LOG_TEST(&m->mtx_object, opts))
664 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
665
666 for (;;) {
667 if (_obtain_lock(m, curthread))
668 break;
669
670 /* Give interrupts a chance while we spin. */
671 critical_exit();
672 while (m->mtx_lock != MTX_UNOWNED) {
673 if (i++ < 10000000) {
674 #ifdef __i386__
675 ia32_pause();
676 #endif
677 continue;
678 }
679 if (i < 60000000)
680 DELAY(1);
681 #ifdef DDB
682 else if (!db_active)
683 #else
684 else
685 #endif
686 panic("spin lock %s held by %p for > 5 seconds",
687 m->mtx_object.lo_name, (void *)m->mtx_lock);
688 #ifdef __i386__
689 ia32_pause();
690 #endif
691 }
692 critical_enter();
693 }
694
695 if (LOCK_LOG_TEST(&m->mtx_object, opts))
696 CTR1(KTR_LOCK, "_mtx_lock_spin: %p spin done", m);
697
698 return;
699 }
700
701 /*
702 * _mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock.
703 *
704 * We are only called here if the lock is recursed or contested (i.e. we
705 * need to wake up a blocked thread).
706 */
707 void
708 _mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
709 {
710 struct thread *td, *td1;
711 struct mtx *m1;
712 int pri;
713
714 td = curthread;
715
716 if (mtx_recursed(m)) {
717 if (--(m->mtx_recurse) == 0)
718 atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED);
719 if (LOCK_LOG_TEST(&m->mtx_object, opts))
720 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p unrecurse", m);
721 return;
722 }
723
724 mtx_lock_spin(&sched_lock);
725 if (LOCK_LOG_TEST(&m->mtx_object, opts))
726 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
727
728 td1 = TAILQ_FIRST(&m->mtx_blocked);
729 #if defined(SMP) && defined(ADAPTIVE_MUTEXES)
730 if (td1 == NULL) {
731 _release_lock_quick(m);
732 if (LOCK_LOG_TEST(&m->mtx_object, opts))
733 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p no sleepers", m);
734 mtx_unlock_spin(&sched_lock);
735 return;
736 }
737 #endif
738 MPASS(td->td_proc->p_magic == P_MAGIC);
739 MPASS(td1->td_proc->p_magic == P_MAGIC);
740
741 TAILQ_REMOVE(&m->mtx_blocked, td1, td_lockq);
742
743 if (TAILQ_EMPTY(&m->mtx_blocked)) {
744 LIST_REMOVE(m, mtx_contested);
745 _release_lock_quick(m);
746 if (LOCK_LOG_TEST(&m->mtx_object, opts))
747 CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p not held", m);
748 } else
749 atomic_store_rel_ptr(&m->mtx_lock, (void *)MTX_CONTESTED);
750
751 pri = PRI_MAX;
752 LIST_FOREACH(m1, &td->td_contested, mtx_contested) {
753 int cp = TAILQ_FIRST(&m1->mtx_blocked)->td_priority;
754 if (cp < pri)
755 pri = cp;
756 }
757
758 if (pri > td->td_base_pri)
759 pri = td->td_base_pri;
760 td->td_priority = pri;
761
762 if (LOCK_LOG_TEST(&m->mtx_object, opts))
763 CTR2(KTR_LOCK, "_mtx_unlock_sleep: %p contested setrunqueue %p",
764 m, td1);
765
766 td1->td_blocked = NULL;
767 TD_CLR_LOCK(td1);
768 if (!TD_CAN_RUN(td1)) {
769 mtx_unlock_spin(&sched_lock);
770 return;
771 }
772 setrunqueue(td1);
773
774 if (td->td_critnest == 1 && td1->td_priority < pri) {
775 #ifdef notyet
776 if (td->td_ithd != NULL) {
777 struct ithd *it = td->td_ithd;
778
779 if (it->it_interrupted) {
780 if (LOCK_LOG_TEST(&m->mtx_object, opts))
781 CTR2(KTR_LOCK,
782 "_mtx_unlock_sleep: %p interrupted %p",
783 it, it->it_interrupted);
784 intr_thd_fixup(it);
785 }
786 }
787 #endif
788 if (LOCK_LOG_TEST(&m->mtx_object, opts))
789 CTR2(KTR_LOCK,
790 "_mtx_unlock_sleep: %p switching out lock=%p", m,
791 (void *)m->mtx_lock);
792
793 td->td_proc->p_stats->p_ru.ru_nivcsw++;
794 mi_switch();
795 if (LOCK_LOG_TEST(&m->mtx_object, opts))
796 CTR2(KTR_LOCK, "_mtx_unlock_sleep: %p resuming lock=%p",
797 m, (void *)m->mtx_lock);
798 }
799
800 mtx_unlock_spin(&sched_lock);
801
802 return;
803 }
804
805 /*
806 * All the unlocking of MTX_SPIN locks is done inline.
807 * See the _rel_spin_lock() macro for the details.
808 */
809
810 /*
811 * The backing function for the INVARIANTS-enabled mtx_assert()
812 */
813 #ifdef INVARIANT_SUPPORT
814 void
815 _mtx_assert(struct mtx *m, int what, const char *file, int line)
816 {
817
818 if (panicstr != NULL)
819 return;
820 switch (what) {
821 case MA_OWNED:
822 case MA_OWNED | MA_RECURSED:
823 case MA_OWNED | MA_NOTRECURSED:
824 if (!mtx_owned(m))
825 panic("mutex %s not owned at %s:%d",
826 m->mtx_object.lo_name, file, line);
827 if (mtx_recursed(m)) {
828 if ((what & MA_NOTRECURSED) != 0)
829 panic("mutex %s recursed at %s:%d",
830 m->mtx_object.lo_name, file, line);
831 } else if ((what & MA_RECURSED) != 0) {
832 panic("mutex %s unrecursed at %s:%d",
833 m->mtx_object.lo_name, file, line);
834 }
835 break;
836 case MA_NOTOWNED:
837 if (mtx_owned(m))
838 panic("mutex %s owned at %s:%d",
839 m->mtx_object.lo_name, file, line);
840 break;
841 default:
842 panic("unknown mtx_assert at %s:%d", file, line);
843 }
844 }
845 #endif
846
847 /*
848 * The MUTEX_DEBUG-enabled mtx_validate()
849 *
850 * Most of these checks have been moved off into the LO_INITIALIZED flag
851 * maintained by the witness code.
852 */
853 #ifdef MUTEX_DEBUG
854
855 void mtx_validate(struct mtx *);
856
857 void
858 mtx_validate(struct mtx *m)
859 {
860
861 /*
862 * XXX: When kernacc() does not require Giant we can reenable this check
863 */
864 #ifdef notyet
865 /*
866 * XXX - When kernacc() is fixed on the alpha to handle K0_SEG memory properly
867 * we can re-enable the kernacc() checks.
868 */
869 #ifndef __alpha__
870 /*
871 * Can't call kernacc() from early init386(), especially when
872 * initializing Giant mutex, because some stuff in kernacc()
873 * requires Giant itself.
874 */
875 if (!cold)
876 if (!kernacc((caddr_t)m, sizeof(m),
877 VM_PROT_READ | VM_PROT_WRITE))
878 panic("Can't read and write to mutex %p", m);
879 #endif
880 #endif
881 }
882 #endif
883
884 /*
885 * General init routine used by the MTX_SYSINIT() macro.
886 */
887 void
888 mtx_sysinit(void *arg)
889 {
890 struct mtx_args *margs = arg;
891
892 mtx_init(margs->ma_mtx, margs->ma_desc, NULL, margs->ma_opts);
893 }
894
895 /*
896 * Mutex initialization routine; initialize lock `m' of type contained in
897 * `opts' with options contained in `opts' and name `name.' The optional
898 * lock type `type' is used as a general lock category name for use with
899 * witness.
900 */
901 void
902 mtx_init(struct mtx *m, const char *name, const char *type, int opts)
903 {
904 struct lock_object *lock;
905
906 MPASS((opts & ~(MTX_SPIN | MTX_QUIET | MTX_RECURSE |
907 MTX_SLEEPABLE | MTX_NOWITNESS | MTX_DUPOK)) == 0);
908
909 #ifdef MUTEX_DEBUG
910 /* Diagnostic and error correction */
911 mtx_validate(m);
912 #endif
913
914 lock = &m->mtx_object;
915 KASSERT((lock->lo_flags & LO_INITIALIZED) == 0,
916 ("mutex %s %p already initialized", name, m));
917 bzero(m, sizeof(*m));
918 if (opts & MTX_SPIN)
919 lock->lo_class = &lock_class_mtx_spin;
920 else
921 lock->lo_class = &lock_class_mtx_sleep;
922 lock->lo_name = name;
923 lock->lo_type = type != NULL ? type : name;
924 if (opts & MTX_QUIET)
925 lock->lo_flags = LO_QUIET;
926 if (opts & MTX_RECURSE)
927 lock->lo_flags |= LO_RECURSABLE;
928 if (opts & MTX_SLEEPABLE)
929 lock->lo_flags |= LO_SLEEPABLE;
930 if ((opts & MTX_NOWITNESS) == 0)
931 lock->lo_flags |= LO_WITNESS;
932 if (opts & MTX_DUPOK)
933 lock->lo_flags |= LO_DUPOK;
934
935 m->mtx_lock = MTX_UNOWNED;
936 TAILQ_INIT(&m->mtx_blocked);
937
938 LOCK_LOG_INIT(lock, opts);
939
940 WITNESS_INIT(lock);
941 }
942
943 /*
944 * Remove lock `m' from all_mtx queue. We don't allow MTX_QUIET to be
945 * passed in as a flag here because if the corresponding mtx_init() was
946 * called with MTX_QUIET set, then it will already be set in the mutex's
947 * flags.
948 */
949 void
950 mtx_destroy(struct mtx *m)
951 {
952
953 LOCK_LOG_DESTROY(&m->mtx_object, 0);
954
955 if (!mtx_owned(m))
956 MPASS(mtx_unowned(m));
957 else {
958 MPASS((m->mtx_lock & (MTX_RECURSED|MTX_CONTESTED)) == 0);
959
960 /* Tell witness this isn't locked to make it happy. */
961 WITNESS_UNLOCK(&m->mtx_object, LOP_EXCLUSIVE, __FILE__,
962 __LINE__);
963 }
964
965 WITNESS_DESTROY(&m->mtx_object);
966 }
967
968 /*
969 * Intialize the mutex code and system mutexes. This is called from the MD
970 * startup code prior to mi_startup(). The per-CPU data space needs to be
971 * setup before this is called.
972 */
973 void
974 mutex_init(void)
975 {
976
977 /* Setup thread0 so that mutexes work. */
978 LIST_INIT(&thread0.td_contested);
979
980 /*
981 * Initialize mutexes.
982 */
983 mtx_init(&Giant, "Giant", NULL, MTX_DEF | MTX_RECURSE);
984 mtx_init(&sched_lock, "sched lock", NULL, MTX_SPIN | MTX_RECURSE);
985 mtx_init(&proc0.p_mtx, "process lock", NULL, MTX_DEF | MTX_DUPOK);
986 mtx_lock(&Giant);
987 }
988
989 /*
990 * Encapsulated Giant mutex routines. These routines provide encapsulation
991 * control for the Giant mutex, allowing sysctls to be used to turn on and
992 * off Giant around certain subsystems. The default value for the sysctls
993 * are set to what developers believe is stable and working in regards to
994 * the Giant pushdown. Developers should not turn off Giant via these
995 * sysctls unless they know what they are doing.
996 *
997 * Callers of mtx_lock_giant() are expected to pass the return value to an
998 * accompanying mtx_unlock_giant() later on. If multiple subsystems are
999 * effected by a Giant wrap, all related sysctl variables must be zero for
1000 * the subsystem call to operate without Giant (as determined by the caller).
1001 */
1002
1003 SYSCTL_NODE(_kern, OID_AUTO, giant, CTLFLAG_RD, NULL, "Giant mutex manipulation");
1004
1005 static int kern_giant_all = 0;
1006 SYSCTL_INT(_kern_giant, OID_AUTO, all, CTLFLAG_RW, &kern_giant_all, 0, "");
1007
1008 int kern_giant_proc = 1; /* Giant around PROC locks */
1009 int kern_giant_file = 1; /* Giant around struct file & filedesc */
1010 int kern_giant_ucred = 1; /* Giant around ucred */
1011 SYSCTL_INT(_kern_giant, OID_AUTO, proc, CTLFLAG_RW, &kern_giant_proc, 0, "");
1012 SYSCTL_INT(_kern_giant, OID_AUTO, file, CTLFLAG_RW, &kern_giant_file, 0, "");
1013 SYSCTL_INT(_kern_giant, OID_AUTO, ucred, CTLFLAG_RW, &kern_giant_ucred, 0, "");
1014
1015 int
1016 mtx_lock_giant(int sysctlvar)
1017 {
1018 if (sysctlvar || kern_giant_all) {
1019 mtx_lock(&Giant);
1020 return(1);
1021 }
1022 return(0);
1023 }
1024
1025 void
1026 mtx_unlock_giant(int s)
1027 {
1028 if (s)
1029 mtx_unlock(&Giant);
1030 }
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