FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_synch.c
1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1982, 1986, 1990, 1991, 1993
5 * The Regents of the University of California. All rights reserved.
6 * (c) UNIX System Laboratories, Inc.
7 * All or some portions of this file are derived from material licensed
8 * to the University of California by American Telephone and Telegraph
9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
10 * the permission of UNIX System Laboratories, Inc.
11 *
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
14 * are met:
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
17 * 2. Redistributions in binary form must reproduce the above copyright
18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 * 3. Neither the name of the University nor the names of its contributors
21 * may be used to endorse or promote products derived from this software
22 * without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 *
36 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95
37 */
38
39 #include <sys/cdefs.h>
40 __FBSDID("$FreeBSD: releng/12.0/sys/kern/kern_synch.c 334026 2018-05-22 08:27:33Z mjg $");
41
42 #include "opt_ktrace.h"
43 #include "opt_sched.h"
44
45 #include <sys/param.h>
46 #include <sys/systm.h>
47 #include <sys/condvar.h>
48 #include <sys/kdb.h>
49 #include <sys/kernel.h>
50 #include <sys/ktr.h>
51 #include <sys/lock.h>
52 #include <sys/mutex.h>
53 #include <sys/proc.h>
54 #include <sys/resourcevar.h>
55 #include <sys/sched.h>
56 #include <sys/sdt.h>
57 #include <sys/signalvar.h>
58 #include <sys/sleepqueue.h>
59 #include <sys/smp.h>
60 #include <sys/sx.h>
61 #include <sys/sysctl.h>
62 #include <sys/sysproto.h>
63 #include <sys/vmmeter.h>
64 #ifdef KTRACE
65 #include <sys/uio.h>
66 #include <sys/ktrace.h>
67 #endif
68
69 #include <machine/cpu.h>
70
71 static void synch_setup(void *dummy);
72 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup,
73 NULL);
74
75 int hogticks;
76 static uint8_t pause_wchan[MAXCPU];
77
78 static struct callout loadav_callout;
79
80 struct loadavg averunnable =
81 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
82 /*
83 * Constants for averages over 1, 5, and 15 minutes
84 * when sampling at 5 second intervals.
85 */
86 static fixpt_t cexp[3] = {
87 0.9200444146293232 * FSCALE, /* exp(-1/12) */
88 0.9834714538216174 * FSCALE, /* exp(-1/60) */
89 0.9944598480048967 * FSCALE, /* exp(-1/180) */
90 };
91
92 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
93 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, SYSCTL_NULL_INT_PTR, FSCALE, "");
94
95 static void loadav(void *arg);
96
97 SDT_PROVIDER_DECLARE(sched);
98 SDT_PROBE_DEFINE(sched, , , preempt);
99
100 static void
101 sleepinit(void *unused)
102 {
103
104 hogticks = (hz / 10) * 2; /* Default only. */
105 init_sleepqueues();
106 }
107
108 /*
109 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure
110 * it is available.
111 */
112 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, NULL);
113
114 /*
115 * General sleep call. Suspends the current thread until a wakeup is
116 * performed on the specified identifier. The thread will then be made
117 * runnable with the specified priority. Sleeps at most sbt units of time
118 * (0 means no timeout). If pri includes the PCATCH flag, let signals
119 * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if
120 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
121 * signal becomes pending, ERESTART is returned if the current system
122 * call should be restarted if possible, and EINTR is returned if the system
123 * call should be interrupted by the signal (return EINTR).
124 *
125 * The lock argument is unlocked before the caller is suspended, and
126 * re-locked before _sleep() returns. If priority includes the PDROP
127 * flag the lock is not re-locked before returning.
128 */
129 int
130 _sleep(void *ident, struct lock_object *lock, int priority,
131 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
132 {
133 struct thread *td;
134 struct lock_class *class;
135 uintptr_t lock_state;
136 int catch, pri, rval, sleepq_flags;
137 WITNESS_SAVE_DECL(lock_witness);
138
139 td = curthread;
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(ident != NULL, ("_sleep: NULL ident"));
149 KASSERT(TD_IS_RUNNING(td), ("_sleep: curthread not running"));
150 KASSERT(td->td_epochnest == 0, ("sleeping in an epoch section"));
151 if (priority & PDROP)
152 KASSERT(lock != NULL && lock != &Giant.lock_object,
153 ("PDROP requires a non-Giant lock"));
154 if (lock != NULL)
155 class = LOCK_CLASS(lock);
156 else
157 class = NULL;
158
159 if (SCHEDULER_STOPPED_TD(td)) {
160 if (lock != NULL && priority & PDROP)
161 class->lc_unlock(lock);
162 return (0);
163 }
164 catch = priority & PCATCH;
165 pri = priority & PRIMASK;
166
167 KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep"));
168
169 if ((uint8_t *)ident >= &pause_wchan[0] &&
170 (uint8_t *)ident <= &pause_wchan[MAXCPU - 1])
171 sleepq_flags = SLEEPQ_PAUSE;
172 else
173 sleepq_flags = SLEEPQ_SLEEP;
174 if (catch)
175 sleepq_flags |= SLEEPQ_INTERRUPTIBLE;
176
177 sleepq_lock(ident);
178 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
179 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
180
181 if (lock == &Giant.lock_object)
182 mtx_assert(&Giant, MA_OWNED);
183 DROP_GIANT();
184 if (lock != NULL && lock != &Giant.lock_object &&
185 !(class->lc_flags & LC_SLEEPABLE)) {
186 WITNESS_SAVE(lock, lock_witness);
187 lock_state = class->lc_unlock(lock);
188 } else
189 /* GCC needs to follow the Yellow Brick Road */
190 lock_state = -1;
191
192 /*
193 * We put ourselves on the sleep queue and start our timeout
194 * before calling thread_suspend_check, as we could stop there,
195 * and a wakeup or a SIGCONT (or both) could occur while we were
196 * stopped without resuming us. Thus, we must be ready for sleep
197 * when cursig() is called. If the wakeup happens while we're
198 * stopped, then td will no longer be on a sleep queue upon
199 * return from cursig().
200 */
201 sleepq_add(ident, lock, wmesg, sleepq_flags, 0);
202 if (sbt != 0)
203 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
204 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
205 sleepq_release(ident);
206 WITNESS_SAVE(lock, lock_witness);
207 lock_state = class->lc_unlock(lock);
208 sleepq_lock(ident);
209 }
210 if (sbt != 0 && catch)
211 rval = sleepq_timedwait_sig(ident, pri);
212 else if (sbt != 0)
213 rval = sleepq_timedwait(ident, pri);
214 else if (catch)
215 rval = sleepq_wait_sig(ident, pri);
216 else {
217 sleepq_wait(ident, pri);
218 rval = 0;
219 }
220 #ifdef KTRACE
221 if (KTRPOINT(td, KTR_CSW))
222 ktrcsw(0, 0, wmesg);
223 #endif
224 PICKUP_GIANT();
225 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
226 class->lc_lock(lock, lock_state);
227 WITNESS_RESTORE(lock, lock_witness);
228 }
229 return (rval);
230 }
231
232 int
233 msleep_spin_sbt(void *ident, struct mtx *mtx, const char *wmesg,
234 sbintime_t sbt, sbintime_t pr, int flags)
235 {
236 struct thread *td;
237 int rval;
238 WITNESS_SAVE_DECL(mtx);
239
240 td = curthread;
241 KASSERT(mtx != NULL, ("sleeping without a mutex"));
242 KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident"));
243 KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running"));
244
245 if (SCHEDULER_STOPPED_TD(td))
246 return (0);
247
248 sleepq_lock(ident);
249 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
250 td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
251
252 DROP_GIANT();
253 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
254 WITNESS_SAVE(&mtx->lock_object, mtx);
255 mtx_unlock_spin(mtx);
256
257 /*
258 * We put ourselves on the sleep queue and start our timeout.
259 */
260 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
261 if (sbt != 0)
262 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
263
264 /*
265 * Can't call ktrace with any spin locks held so it can lock the
266 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
267 * any spin lock. Thus, we have to drop the sleepq spin lock while
268 * we handle those requests. This is safe since we have placed our
269 * thread on the sleep queue already.
270 */
271 #ifdef KTRACE
272 if (KTRPOINT(td, KTR_CSW)) {
273 sleepq_release(ident);
274 ktrcsw(1, 0, wmesg);
275 sleepq_lock(ident);
276 }
277 #endif
278 #ifdef WITNESS
279 sleepq_release(ident);
280 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
281 wmesg);
282 sleepq_lock(ident);
283 #endif
284 if (sbt != 0)
285 rval = sleepq_timedwait(ident, 0);
286 else {
287 sleepq_wait(ident, 0);
288 rval = 0;
289 }
290 #ifdef KTRACE
291 if (KTRPOINT(td, KTR_CSW))
292 ktrcsw(0, 0, wmesg);
293 #endif
294 PICKUP_GIANT();
295 mtx_lock_spin(mtx);
296 WITNESS_RESTORE(&mtx->lock_object, mtx);
297 return (rval);
298 }
299
300 /*
301 * pause_sbt() delays the calling thread by the given signed binary
302 * time. During cold bootup, pause_sbt() uses the DELAY() function
303 * instead of the _sleep() function to do the waiting. The "sbt"
304 * argument must be greater than or equal to zero. A "sbt" value of
305 * zero is equivalent to a "sbt" value of one tick.
306 */
307 int
308 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
309 {
310 KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0"));
311
312 /* silently convert invalid timeouts */
313 if (sbt == 0)
314 sbt = tick_sbt;
315
316 if ((cold && curthread == &thread0) || kdb_active ||
317 SCHEDULER_STOPPED()) {
318 /*
319 * We delay one second at a time to avoid overflowing the
320 * system specific DELAY() function(s):
321 */
322 while (sbt >= SBT_1S) {
323 DELAY(1000000);
324 sbt -= SBT_1S;
325 }
326 /* Do the delay remainder, if any */
327 sbt = howmany(sbt, SBT_1US);
328 if (sbt > 0)
329 DELAY(sbt);
330 return (EWOULDBLOCK);
331 }
332 return (_sleep(&pause_wchan[curcpu], NULL,
333 (flags & C_CATCH) ? PCATCH : 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 VM_CNT_INC(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 (__predict_false(sdt_probes_enabled) &&
435 ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
436 (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED)))
437 SDT_PROBE0(sched, , , preempt);
438 #endif
439 sched_switch(td, newtd, flags);
440 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
441 td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
442
443 /*
444 * If the last thread was exiting, finish cleaning it up.
445 */
446 if ((td = PCPU_GET(deadthread))) {
447 PCPU_SET(deadthread, NULL);
448 thread_stash(td);
449 }
450 }
451
452 /*
453 * Change thread state to be runnable, placing it on the run queue if
454 * it is in memory. If it is swapped out, return true so our caller
455 * will know to awaken the swapper.
456 */
457 int
458 setrunnable(struct thread *td)
459 {
460
461 THREAD_LOCK_ASSERT(td, MA_OWNED);
462 KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
463 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
464 switch (td->td_state) {
465 case TDS_RUNNING:
466 case TDS_RUNQ:
467 return (0);
468 case TDS_INHIBITED:
469 /*
470 * If we are only inhibited because we are swapped out
471 * then arange to swap in this process. Otherwise just return.
472 */
473 if (td->td_inhibitors != TDI_SWAPPED)
474 return (0);
475 /* FALLTHROUGH */
476 case TDS_CAN_RUN:
477 break;
478 default:
479 printf("state is 0x%x", td->td_state);
480 panic("setrunnable(2)");
481 }
482 if ((td->td_flags & TDF_INMEM) == 0) {
483 if ((td->td_flags & TDF_SWAPINREQ) == 0) {
484 td->td_flags |= TDF_SWAPINREQ;
485 return (1);
486 }
487 } else
488 sched_wakeup(td);
489 return (0);
490 }
491
492 /*
493 * Compute a tenex style load average of a quantity on
494 * 1, 5 and 15 minute intervals.
495 */
496 static void
497 loadav(void *arg)
498 {
499 int i, nrun;
500 struct loadavg *avg;
501
502 nrun = sched_load();
503 avg = &averunnable;
504
505 for (i = 0; i < 3; i++)
506 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
507 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
508
509 /*
510 * Schedule the next update to occur after 5 seconds, but add a
511 * random variation to avoid synchronisation with processes that
512 * run at regular intervals.
513 */
514 callout_reset_sbt(&loadav_callout,
515 SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US,
516 loadav, NULL, C_DIRECT_EXEC | C_PREL(32));
517 }
518
519 /* ARGSUSED */
520 static void
521 synch_setup(void *dummy)
522 {
523 callout_init(&loadav_callout, 1);
524
525 /* Kick off timeout driven events by calling first time. */
526 loadav(NULL);
527 }
528
529 int
530 should_yield(void)
531 {
532
533 return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
534 }
535
536 void
537 maybe_yield(void)
538 {
539
540 if (should_yield())
541 kern_yield(PRI_USER);
542 }
543
544 void
545 kern_yield(int prio)
546 {
547 struct thread *td;
548
549 td = curthread;
550 DROP_GIANT();
551 thread_lock(td);
552 if (prio == PRI_USER)
553 prio = td->td_user_pri;
554 if (prio >= 0)
555 sched_prio(td, prio);
556 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
557 thread_unlock(td);
558 PICKUP_GIANT();
559 }
560
561 /*
562 * General purpose yield system call.
563 */
564 int
565 sys_yield(struct thread *td, struct yield_args *uap)
566 {
567
568 thread_lock(td);
569 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
570 sched_prio(td, PRI_MAX_TIMESHARE);
571 mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
572 thread_unlock(td);
573 td->td_retval[0] = 0;
574 return (0);
575 }
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