3 * The Regents of the University of California. All rights reserved.
6 * John S. Dyson. All rights reserved.
8 * This code contains ideas from software contributed to Berkeley by
9 * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
10 * System project at Carnegie-Mellon University.
12 * Redistribution and use in source and binary forms, with or without
13 * modification, are permitted provided that the following conditions
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
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18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 * 3. All advertising materials mentioning features or use of this software
21 * must display the following acknowledgement:
22 * This product includes software developed by the University of
23 * California, Berkeley and its contributors.
24 * 4. Neither the name of the University nor the names of its contributors
25 * may be used to endorse or promote products derived from this software
26 * without specific prior written permission.
28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
40 * @(#)kern_lock.c 8.18 (Berkeley) 5/21/95
41 * $FreeBSD: src/sys/kern/kern_lock.c,v 1.31.2.3 2001/12/25 01:44:44 dillon Exp $
42 * $DragonFly: src/sys/kern/kern_lock.c,v 1.15 2005/11/19 17:19:47 dillon Exp $
47 #include <sys/param.h>
48 #include <sys/systm.h>
49 #include <sys/kernel.h>
52 #include <sys/sysctl.h>
53 #include <sys/spinlock.h>
54 #include <sys/thread2.h>
55 #include <sys/spinlock2.h>
58 * 0: no warnings, 1: warnings, 2: panic
60 static int lockmgr_from_int = 1;
61 SYSCTL_INT(_debug, OID_AUTO, lockmgr_from_int, CTLFLAG_RW, &lockmgr_from_int, 0, "");
64 * Locking primitives implementation.
65 * Locks provide shared/exclusive sychronization.
68 #ifdef SIMPLELOCK_DEBUG
69 #define COUNT(td, x) (td)->td_locks += (x)
74 #define LOCK_WAIT_TIME 100
75 #define LOCK_SAMPLE_WAIT 7
77 #if defined(DIAGNOSTIC)
80 #define LOCK_INLINE __inline
83 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
84 LK_SHARE_NONZERO | LK_WAIT_NONZERO)
86 static int acquire(struct lock *lkp, int extflags, int wanted);
87 static int acquiredrain(struct lock *lkp, int extflags) ;
89 static LOCK_INLINE void
90 sharelock(struct lock *lkp, int incr) {
91 lkp->lk_flags |= LK_SHARE_NONZERO;
92 lkp->lk_sharecount += incr;
95 static LOCK_INLINE void
96 shareunlock(struct lock *lkp, int decr) {
98 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
100 if (lkp->lk_sharecount == decr) {
101 lkp->lk_flags &= ~LK_SHARE_NONZERO;
102 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
105 lkp->lk_sharecount = 0;
107 lkp->lk_sharecount -= decr;
112 * lock acquisition helper routine. Called with the lock's spinlock held.
115 acquire(struct lock *lkp, int extflags, int wanted)
119 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
123 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
124 if ((lkp->lk_flags & wanted) == 0)
128 while ((lkp->lk_flags & wanted) != 0) {
129 lkp->lk_flags |= LK_WAIT_NONZERO;
133 * Use the _quick version so the critical section is left
134 * intact, protecting the tsleep interlock. See
135 * tsleep_interlock() for a description of what is
138 tsleep_interlock(lkp);
139 spin_unlock_quick(&lkp->lk_spinlock);
140 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg,
141 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
142 spin_lock_quick(&lkp->lk_spinlock);
143 if (lkp->lk_waitcount == 1) {
144 lkp->lk_flags &= ~LK_WAIT_NONZERO;
145 lkp->lk_waitcount = 0;
151 if (extflags & LK_SLEEPFAIL)
158 * Set, change, or release a lock.
160 * Shared requests increment the shared count. Exclusive requests set the
161 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
162 * accepted shared locks and shared-to-exclusive upgrades to go away.
164 * A spinlock is held for most of the procedure. We must not do anything
165 * fancy while holding the spinlock.
169 lockmgr(struct lock *lkp, u_int flags, struct spinlock *interlkp,
172 debuglockmgr(struct lock *lkp, u_int flags, struct spinlock *interlkp,
173 struct thread *td, const char *name, const char *file, int line)
182 if (lockmgr_from_int && mycpu->gd_intr_nesting_level &&
183 (flags & LK_NOWAIT) == 0 &&
184 (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) {
186 if (lockmgr_from_int == 2) {
188 if (flags & LK_INTERLOCK)
189 spin_unlock(interlkp);
191 "lockmgr %s from %p: called from interrupt",
192 lkp->lk_wmesg, ((int **)&lkp)[-1]);
196 "lockmgr %s from %p: called from interrupt\n",
197 lkp->lk_wmesg, ((int **)&lkp)[-1]);
200 if (lockmgr_from_int == 2) {
202 if (flags & LK_INTERLOCK)
203 spin_unlock(interlkp);
205 "lockmgr %s from %s:%d: called from interrupt",
206 lkp->lk_wmesg, file, line);
210 "lockmgr %s from %s:%d: called from interrupt\n",
211 lkp->lk_wmesg, file, line);
216 spin_lock(&lkp->lk_spinlock);
217 if (flags & LK_INTERLOCK)
218 spin_unlock(interlkp);
220 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
222 switch (flags & LK_TYPE_MASK) {
225 * If we are not the exclusive lock holder, we have to block
226 * while there is an exclusive lock holder or while an
227 * exclusive lock request or upgrade request is in progress.
229 * However, if P_DEADLKTREAT is set, we override exclusive
230 * lock requests or upgrade requests ( but not the exclusive
233 if (lkp->lk_lockholder != td) {
234 if (td->td_flags & TDF_DEADLKTREAT) {
244 LK_HAVE_EXCL | LK_WANT_EXCL |
255 * We hold an exclusive lock, so downgrade it to shared.
256 * An alternative would be to fail with EDEADLK.
260 /* fall into downgrade */
263 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) {
264 spin_unlock(&lkp->lk_spinlock);
265 panic("lockmgr: not holding exclusive lock");
267 sharelock(lkp, lkp->lk_exclusivecount);
268 lkp->lk_exclusivecount = 0;
269 lkp->lk_flags &= ~LK_HAVE_EXCL;
270 lkp->lk_lockholder = LK_NOTHREAD;
271 if (lkp->lk_waitcount)
277 * If another process is ahead of us to get an upgrade,
278 * then we want to fail rather than have an intervening
281 if (lkp->lk_flags & LK_WANT_UPGRADE) {
287 /* fall into normal upgrade */
291 * Upgrade a shared lock to an exclusive one. If another
292 * shared lock has already requested an upgrade to an
293 * exclusive lock, our shared lock is released and an
294 * exclusive lock is requested (which will be granted
295 * after the upgrade). If we return an error, the file
296 * will always be unlocked.
298 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) {
299 spin_unlock(&lkp->lk_spinlock);
300 panic("lockmgr: upgrade exclusive lock");
305 * If we are just polling, check to see if we will block.
307 if ((extflags & LK_NOWAIT) &&
308 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
309 lkp->lk_sharecount > 1)) {
313 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
315 * We are first shared lock to request an upgrade, so
316 * request upgrade and wait for the shared count to
317 * drop to zero, then take exclusive lock.
319 lkp->lk_flags |= LK_WANT_UPGRADE;
320 error = acquire(lkp, extflags, LK_SHARE_NONZERO);
321 lkp->lk_flags &= ~LK_WANT_UPGRADE;
325 lkp->lk_flags |= LK_HAVE_EXCL;
326 lkp->lk_lockholder = td;
327 if (lkp->lk_exclusivecount != 0) {
328 spin_unlock(&lkp->lk_spinlock);
329 panic("lockmgr: non-zero exclusive count");
331 lkp->lk_exclusivecount = 1;
332 #if defined(DEBUG_LOCKS)
333 lkp->lk_filename = file;
334 lkp->lk_lineno = line;
335 lkp->lk_lockername = name;
341 * Someone else has requested upgrade. Release our shared
342 * lock, awaken upgrade requestor if we are the last shared
343 * lock, then request an exclusive lock.
345 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
348 /* fall into exclusive request */
351 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
355 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) {
356 spin_unlock(&lkp->lk_spinlock);
357 panic("lockmgr: locking against myself");
359 if ((extflags & LK_CANRECURSE) != 0) {
360 lkp->lk_exclusivecount++;
366 * If we are just polling, check to see if we will sleep.
368 if ((extflags & LK_NOWAIT) &&
369 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
374 * Try to acquire the want_exclusive flag.
376 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
379 lkp->lk_flags |= LK_WANT_EXCL;
381 * Wait for shared locks and upgrades to finish.
383 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
384 lkp->lk_flags &= ~LK_WANT_EXCL;
387 lkp->lk_flags |= LK_HAVE_EXCL;
388 lkp->lk_lockholder = td;
389 if (lkp->lk_exclusivecount != 0) {
390 spin_unlock(&lkp->lk_spinlock);
391 panic("lockmgr: non-zero exclusive count");
393 lkp->lk_exclusivecount = 1;
394 #if defined(DEBUG_LOCKS)
395 lkp->lk_filename = file;
396 lkp->lk_lineno = line;
397 lkp->lk_lockername = name;
403 if (lkp->lk_exclusivecount != 0) {
404 if (lkp->lk_lockholder != td &&
405 lkp->lk_lockholder != LK_KERNTHREAD) {
406 spin_unlock(&lkp->lk_spinlock);
407 panic("lockmgr: pid %d, not %s thr %p unlocking",
408 (td->td_proc ? td->td_proc->p_pid : -99),
409 "exclusive lock holder",
412 if (lkp->lk_lockholder != LK_KERNTHREAD) {
415 if (lkp->lk_exclusivecount == 1) {
416 lkp->lk_flags &= ~LK_HAVE_EXCL;
417 lkp->lk_lockholder = LK_NOTHREAD;
418 lkp->lk_exclusivecount = 0;
420 lkp->lk_exclusivecount--;
422 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
426 if (lkp->lk_flags & LK_WAIT_NONZERO)
432 * Check that we do not already hold the lock, as it can
433 * never drain if we do. Unfortunately, we have no way to
434 * check for holding a shared lock, but at least we can
435 * check for an exclusive one.
437 if (lkp->lk_lockholder == td) {
438 spin_unlock(&lkp->lk_spinlock);
439 panic("lockmgr: draining against myself");
442 error = acquiredrain(lkp, extflags);
445 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
446 lkp->lk_lockholder = td;
447 lkp->lk_exclusivecount = 1;
448 #if defined(DEBUG_LOCKS)
449 lkp->lk_filename = file;
450 lkp->lk_lineno = line;
451 lkp->lk_lockername = name;
457 spin_unlock(&lkp->lk_spinlock);
458 panic("lockmgr: unknown locktype request %d",
459 flags & LK_TYPE_MASK);
462 if ((lkp->lk_flags & LK_WAITDRAIN) &&
463 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
464 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
465 lkp->lk_flags &= ~LK_WAITDRAIN;
466 wakeup((void *)&lkp->lk_flags);
468 spin_unlock(&lkp->lk_spinlock);
473 * lock acquisition helper routine. Called with the lock's spinlock held.
476 acquiredrain(struct lock *lkp, int extflags)
480 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
484 if ((lkp->lk_flags & LK_ALL) == 0)
487 while (lkp->lk_flags & LK_ALL) {
488 lkp->lk_flags |= LK_WAITDRAIN;
490 * Use the _quick version so the critical section is left
491 * intact, protecting the tsleep interlock. See
492 * tsleep_interlock() for a description of what is
495 tsleep_interlock(&lkp->lk_flags);
496 spin_unlock_quick(&lkp->lk_spinlock);
497 error = tsleep(&lkp->lk_flags, lkp->lk_prio,
499 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
500 spin_lock_quick(&lkp->lk_spinlock);
503 if (extflags & LK_SLEEPFAIL) {
511 * Initialize a lock; required before use.
514 lockinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags)
516 spin_init(&lkp->lk_spinlock);
517 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
518 lkp->lk_sharecount = 0;
519 lkp->lk_waitcount = 0;
520 lkp->lk_exclusivecount = 0;
522 lkp->lk_wmesg = wmesg;
524 lkp->lk_lockholder = LK_NOTHREAD;
528 * Reinitialize a lock that is being reused for a different purpose, but
529 * which may have pending (blocked) threads sitting on it. The caller
530 * must already hold the interlock.
533 lockreinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags)
535 lkp->lk_flags = (lkp->lk_flags & ~(LK_EXTFLG_MASK|LK_DRAINING)) |
536 (flags & LK_EXTFLG_MASK);
538 lkp->lk_wmesg = wmesg;
543 * Determine the status of a lock.
546 lockstatus(struct lock *lkp, struct thread *td)
550 spin_lock(&lkp->lk_spinlock);
551 if (lkp->lk_exclusivecount != 0) {
552 if (td == NULL || lkp->lk_lockholder == td)
553 lock_type = LK_EXCLUSIVE;
555 lock_type = LK_EXCLOTHER;
556 } else if (lkp->lk_sharecount != 0) {
557 lock_type = LK_SHARED;
559 spin_unlock(&lkp->lk_spinlock);
564 * Determine the number of holders of a lock.
566 * The non-blocking version can usually be used for assertions.
569 lockcount(struct lock *lkp)
573 spin_lock(&lkp->lk_spinlock);
574 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
575 spin_unlock(&lkp->lk_spinlock);
580 lockcountnb(struct lock *lkp)
582 return (lkp->lk_exclusivecount + lkp->lk_sharecount);
586 * Print out information about state of a lock. Used by VOP_PRINT
587 * routines to display status about contained locks.
590 lockmgr_printinfo(struct lock *lkp)
592 struct thread *td = lkp->lk_lockholder;
595 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
600 if (lkp->lk_sharecount)
601 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
603 else if (lkp->lk_flags & LK_HAVE_EXCL)
604 printf(" lock type %s: EXCL (count %d) by td %p pid %d",
605 lkp->lk_wmesg, lkp->lk_exclusivecount, td,
607 if (lkp->lk_waitcount > 0)
608 printf(" with %d pending", lkp->lk_waitcount);