FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_synch.c
1 /*-
2 * Copyright (c) 1982, 1986, 1990, 1991, 1993
3 * The Regents of the University of California. All rights reserved.
4 * (c) UNIX System Laboratories, Inc.
5 * All or some portions of this file are derived from material licensed
6 * to the University of California by American Telephone and Telegraph
7 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
8 * the permission of UNIX System Laboratories, Inc.
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 * 4. Neither the name of the University nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 *
34 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95
35 */
36
37 #include <sys/cdefs.h>
38 __FBSDID("$FreeBSD: releng/11.1/sys/kern/kern_synch.c 316842 2017-04-14 14:45:39Z avg $");
39
40 #include "opt_ktrace.h"
41 #include "opt_sched.h"
42
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/condvar.h>
46 #include <sys/kdb.h>
47 #include <sys/kernel.h>
48 #include <sys/ktr.h>
49 #include <sys/lock.h>
50 #include <sys/mutex.h>
51 #include <sys/proc.h>
52 #include <sys/resourcevar.h>
53 #include <sys/sched.h>
54 #include <sys/sdt.h>
55 #include <sys/signalvar.h>
56 #include <sys/sleepqueue.h>
57 #include <sys/smp.h>
58 #include <sys/sx.h>
59 #include <sys/sysctl.h>
60 #include <sys/sysproto.h>
61 #include <sys/vmmeter.h>
62 #ifdef KTRACE
63 #include <sys/uio.h>
64 #include <sys/ktrace.h>
65 #endif
66
67 #include <machine/cpu.h>
68
69 static void synch_setup(void *dummy);
70 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup,
71 NULL);
72
73 int hogticks;
74 static uint8_t pause_wchan[MAXCPU];
75
76 static struct callout loadav_callout;
77
78 struct loadavg averunnable =
79 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
80 /*
81 * Constants for averages over 1, 5, and 15 minutes
82 * when sampling at 5 second intervals.
83 */
84 static fixpt_t cexp[3] = {
85 0.9200444146293232 * FSCALE, /* exp(-1/12) */
86 0.9834714538216174 * FSCALE, /* exp(-1/60) */
87 0.9944598480048967 * FSCALE, /* exp(-1/180) */
88 };
89
90 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
91 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, SYSCTL_NULL_INT_PTR, FSCALE, "");
92
93 static void loadav(void *arg);
94
95 SDT_PROVIDER_DECLARE(sched);
96 SDT_PROBE_DEFINE(sched, , , preempt);
97
98 static void
99 sleepinit(void *unused)
100 {
101
102 hogticks = (hz / 10) * 2; /* Default only. */
103 init_sleepqueues();
104 }
105
106 /*
107 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure
108 * it is available.
109 */
110 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, 0);
111
112 /*
113 * General sleep call. Suspends the current thread until a wakeup is
114 * performed on the specified identifier. The thread will then be made
115 * runnable with the specified priority. Sleeps at most sbt units of time
116 * (0 means no timeout). If pri includes the PCATCH flag, let signals
117 * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if
118 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
119 * signal becomes pending, ERESTART is returned if the current system
120 * call should be restarted if possible, and EINTR is returned if the system
121 * call should be interrupted by the signal (return EINTR).
122 *
123 * The lock argument is unlocked before the caller is suspended, and
124 * re-locked before _sleep() returns. If priority includes the PDROP
125 * flag the lock is not re-locked before returning.
126 */
127 int
128 _sleep(void *ident, struct lock_object *lock, int priority,
129 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
130 {
131 struct thread *td;
132 struct proc *p;
133 struct lock_class *class;
134 uintptr_t lock_state;
135 int catch, pri, rval, sleepq_flags;
136 WITNESS_SAVE_DECL(lock_witness);
137
138 td = curthread;
139 p = td->td_proc;
140 #ifdef KTRACE
141 if (KTRPOINT(td, KTR_CSW))
142 ktrcsw(1, 0, wmesg);
143 #endif
144 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
145 "Sleeping on \"%s\"", wmesg);
146 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL,
147 ("sleeping without a lock"));
148 KASSERT(p != NULL, ("msleep1"));
149 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
150 if (priority & PDROP)
151 KASSERT(lock != NULL && lock != &Giant.lock_object,
152 ("PDROP requires a non-Giant lock"));
153 if (lock != NULL)
154 class = LOCK_CLASS(lock);
155 else
156 class = NULL;
157
158 if (SCHEDULER_STOPPED_TD(td)) {
159 if (lock != NULL && priority & PDROP)
160 class->lc_unlock(lock);
161 return (0);
162 }
163 catch = priority & PCATCH;
164 pri = priority & PRIMASK;
165
166 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep"));
167
168 if ((uint8_t *)ident >= &pause_wchan[0] &&
169 (uint8_t *)ident <= &pause_wchan[MAXCPU - 1])
170 sleepq_flags = SLEEPQ_PAUSE;
171 else
172 sleepq_flags = SLEEPQ_SLEEP;
173 if (catch)
174 sleepq_flags |= SLEEPQ_INTERRUPTIBLE;
175
176 sleepq_lock(ident);
177 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
178 td->td_tid, p->p_pid, td->td_name, wmesg, ident);
179
180 if (lock == &Giant.lock_object)
181 mtx_assert(&Giant, MA_OWNED);
182 DROP_GIANT();
183 if (lock != NULL && lock != &Giant.lock_object &&
184 !(class->lc_flags & LC_SLEEPABLE)) {
185 WITNESS_SAVE(lock, lock_witness);
186 lock_state = class->lc_unlock(lock);
187 } else
188 /* GCC needs to follow the Yellow Brick Road */
189 lock_state = -1;
190
191 /*
192 * We put ourselves on the sleep queue and start our timeout
193 * before calling thread_suspend_check, as we could stop there,
194 * and a wakeup or a SIGCONT (or both) could occur while we were
195 * stopped without resuming us. Thus, we must be ready for sleep
196 * when cursig() is called. If the wakeup happens while we're
197 * stopped, then td will no longer be on a sleep queue upon
198 * return from cursig().
199 */
200 sleepq_add(ident, lock, wmesg, sleepq_flags, 0);
201 if (sbt != 0)
202 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
203 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
204 sleepq_release(ident);
205 WITNESS_SAVE(lock, lock_witness);
206 lock_state = class->lc_unlock(lock);
207 sleepq_lock(ident);
208 }
209 if (sbt != 0 && catch)
210 rval = sleepq_timedwait_sig(ident, pri);
211 else if (sbt != 0)
212 rval = sleepq_timedwait(ident, pri);
213 else if (catch)
214 rval = sleepq_wait_sig(ident, pri);
215 else {
216 sleepq_wait(ident, pri);
217 rval = 0;
218 }
219 #ifdef KTRACE
220 if (KTRPOINT(td, KTR_CSW))
221 ktrcsw(0, 0, wmesg);
222 #endif
223 PICKUP_GIANT();
224 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
225 class->lc_lock(lock, lock_state);
226 WITNESS_RESTORE(lock, lock_witness);
227 }
228 return (rval);
229 }
230
231 int
232 msleep_spin_sbt(void *ident, struct mtx *mtx, const char *wmesg,
233 sbintime_t sbt, sbintime_t pr, int flags)
234 {
235 struct thread *td;
236 struct proc *p;
237 int rval;
238 WITNESS_SAVE_DECL(mtx);
239
240 td = curthread;
241 p = td->td_proc;
242 KASSERT(mtx != NULL, ("sleeping without a mutex"));
243 KASSERT(p != NULL, ("msleep1"));
244 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
245
246 if (SCHEDULER_STOPPED_TD(td))
247 return (0);
248
249 sleepq_lock(ident);
250 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
251 td->td_tid, p->p_pid, td->td_name, wmesg, ident);
252
253 DROP_GIANT();
254 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
255 WITNESS_SAVE(&mtx->lock_object, mtx);
256 mtx_unlock_spin(mtx);
257
258 /*
259 * We put ourselves on the sleep queue and start our timeout.
260 */
261 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
262 if (sbt != 0)
263 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
264
265 /*
266 * Can't call ktrace with any spin locks held so it can lock the
267 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
268 * any spin lock. Thus, we have to drop the sleepq spin lock while
269 * we handle those requests. This is safe since we have placed our
270 * thread on the sleep queue already.
271 */
272 #ifdef KTRACE
273 if (KTRPOINT(td, KTR_CSW)) {
274 sleepq_release(ident);
275 ktrcsw(1, 0, wmesg);
276 sleepq_lock(ident);
277 }
278 #endif
279 #ifdef WITNESS
280 sleepq_release(ident);
281 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
282 wmesg);
283 sleepq_lock(ident);
284 #endif
285 if (sbt != 0)
286 rval = sleepq_timedwait(ident, 0);
287 else {
288 sleepq_wait(ident, 0);
289 rval = 0;
290 }
291 #ifdef KTRACE
292 if (KTRPOINT(td, KTR_CSW))
293 ktrcsw(0, 0, wmesg);
294 #endif
295 PICKUP_GIANT();
296 mtx_lock_spin(mtx);
297 WITNESS_RESTORE(&mtx->lock_object, mtx);
298 return (rval);
299 }
300
301 /*
302 * pause() delays the calling thread by the given number of system ticks.
303 * During cold bootup, pause() uses the DELAY() function instead of
304 * the tsleep() function to do the waiting. The "timo" argument must be
305 * greater than or equal to zero. A "timo" value of zero is equivalent
306 * to a "timo" value of one.
307 */
308 int
309 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
310 {
311 KASSERT(sbt >= 0, ("pause: timeout must be >= 0"));
312
313 /* silently convert invalid timeouts */
314 if (sbt == 0)
315 sbt = tick_sbt;
316
317 if ((cold && curthread == &thread0) || kdb_active ||
318 SCHEDULER_STOPPED()) {
319 /*
320 * We delay one second at a time to avoid overflowing the
321 * system specific DELAY() function(s):
322 */
323 while (sbt >= SBT_1S) {
324 DELAY(1000000);
325 sbt -= SBT_1S;
326 }
327 /* Do the delay remainder, if any */
328 sbt = howmany(sbt, SBT_1US);
329 if (sbt > 0)
330 DELAY(sbt);
331 return (0);
332 }
333 return (_sleep(&pause_wchan[curcpu], NULL, 0, wmesg, sbt, pr, flags));
334 }
335
336 /*
337 * Make all threads sleeping on the specified identifier runnable.
338 */
339 void
340 wakeup(void *ident)
341 {
342 int wakeup_swapper;
343
344 sleepq_lock(ident);
345 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
346 sleepq_release(ident);
347 if (wakeup_swapper) {
348 KASSERT(ident != &proc0,
349 ("wakeup and wakeup_swapper and proc0"));
350 kick_proc0();
351 }
352 }
353
354 /*
355 * Make a thread sleeping on the specified identifier runnable.
356 * May wake more than one thread if a target thread is currently
357 * swapped out.
358 */
359 void
360 wakeup_one(void *ident)
361 {
362 int wakeup_swapper;
363
364 sleepq_lock(ident);
365 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
366 sleepq_release(ident);
367 if (wakeup_swapper)
368 kick_proc0();
369 }
370
371 static void
372 kdb_switch(void)
373 {
374 thread_unlock(curthread);
375 kdb_backtrace();
376 kdb_reenter();
377 panic("%s: did not reenter debugger", __func__);
378 }
379
380 /*
381 * The machine independent parts of context switching.
382 */
383 void
384 mi_switch(int flags, struct thread *newtd)
385 {
386 uint64_t runtime, new_switchtime;
387 struct thread *td;
388
389 td = curthread; /* XXX */
390 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
391 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
392 #ifdef INVARIANTS
393 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
394 mtx_assert(&Giant, MA_NOTOWNED);
395 #endif
396 KASSERT(td->td_critnest == 1 || panicstr,
397 ("mi_switch: switch in a critical section"));
398 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
399 ("mi_switch: switch must be voluntary or involuntary"));
400 KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
401
402 /*
403 * Don't perform context switches from the debugger.
404 */
405 if (kdb_active)
406 kdb_switch();
407 if (SCHEDULER_STOPPED_TD(td))
408 return;
409 if (flags & SW_VOL) {
410 td->td_ru.ru_nvcsw++;
411 td->td_swvoltick = ticks;
412 } else {
413 td->td_ru.ru_nivcsw++;
414 td->td_swinvoltick = ticks;
415 }
416 #ifdef SCHED_STATS
417 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
418 #endif
419 /*
420 * Compute the amount of time during which the current
421 * thread was running, and add that to its total so far.
422 */
423 new_switchtime = cpu_ticks();
424 runtime = new_switchtime - PCPU_GET(switchtime);
425 td->td_runtime += runtime;
426 td->td_incruntime += runtime;
427 PCPU_SET(switchtime, new_switchtime);
428 td->td_generation++; /* bump preempt-detect counter */
429 PCPU_INC(cnt.v_swtch);
430 PCPU_SET(switchticks, ticks);
431 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
432 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
433 #ifdef KDTRACE_HOOKS
434 if ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
435 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED))
436 SDT_PROBE0(sched, , , preempt);
437 #endif
438 sched_switch(td, newtd, flags);
439 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
440 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
441
442 /*
443 * If the last thread was exiting, finish cleaning it up.
444 */
445 if ((td = PCPU_GET(deadthread))) {
446 PCPU_SET(deadthread, NULL);
447 thread_stash(td);
448 }
449 }
450
451 /*
452 * Change thread state to be runnable, placing it on the run queue if
453 * it is in memory. If it is swapped out, return true so our caller
454 * will know to awaken the swapper.
455 */
456 int
457 setrunnable(struct thread *td)
458 {
459
460 THREAD_LOCK_ASSERT(td, MA_OWNED);
461 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
462 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
463 switch (td->td_state) {
464 case TDS_RUNNING:
465 case TDS_RUNQ:
466 return (0);
467 case TDS_INHIBITED:
468 /*
469 * If we are only inhibited because we are swapped out
470 * then arange to swap in this process. Otherwise just return.
471 */
472 if (td->td_inhibitors != TDI_SWAPPED)
473 return (0);
474 /* FALLTHROUGH */
475 case TDS_CAN_RUN:
476 break;
477 default:
478 printf("state is 0x%x", td->td_state);
479 panic("setrunnable(2)");
480 }
481 if ((td->td_flags & TDF_INMEM) == 0) {
482 if ((td->td_flags & TDF_SWAPINREQ) == 0) {
483 td->td_flags |= TDF_SWAPINREQ;
484 return (1);
485 }
486 } else
487 sched_wakeup(td);
488 return (0);
489 }
490
491 /*
492 * Compute a tenex style load average of a quantity on
493 * 1, 5 and 15 minute intervals.
494 */
495 static void
496 loadav(void *arg)
497 {
498 int i, nrun;
499 struct loadavg *avg;
500
501 nrun = sched_load();
502 avg = &averunnable;
503
504 for (i = 0; i < 3; i++)
505 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
506 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
507
508 /*
509 * Schedule the next update to occur after 5 seconds, but add a
510 * random variation to avoid synchronisation with processes that
511 * run at regular intervals.
512 */
513 callout_reset_sbt(&loadav_callout,
514 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US,
515 loadav, NULL, C_DIRECT_EXEC | C_PREL(32));
516 }
517
518 /* ARGSUSED */
519 static void
520 synch_setup(void *dummy)
521 {
522 callout_init(&loadav_callout, 1);
523
524 /* Kick off timeout driven events by calling first time. */
525 loadav(NULL);
526 }
527
528 int
529 should_yield(void)
530 {
531
532 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
533 }
534
535 void
536 maybe_yield(void)
537 {
538
539 if (should_yield())
540 kern_yield(PRI_USER);
541 }
542
543 void
544 kern_yield(int prio)
545 {
546 struct thread *td;
547
548 td = curthread;
549 DROP_GIANT();
550 thread_lock(td);
551 if (prio == PRI_USER)
552 prio = td->td_user_pri;
553 if (prio >= 0)
554 sched_prio(td, prio);
555 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
556 thread_unlock(td);
557 PICKUP_GIANT();
558 }
559
560 /*
561 * General purpose yield system call.
562 */
563 int
564 sys_yield(struct thread *td, struct yield_args *uap)
565 {
566
567 thread_lock(td);
568 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
569 sched_prio(td, PRI_MAX_TIMESHARE);
570 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
571 thread_unlock(td);
572 td->td_retval[0] = 0;
573 return (0);
574 }
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