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
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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.
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34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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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 1.27 2008/01/09 10:59:12 corecode 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 * Locking primitives implementation.
59 * Locks provide shared/exclusive sychronization.
63 #define COUNT(td, x) (td)->td_locks += (x)
68 #define LOCK_WAIT_TIME 100
69 #define LOCK_SAMPLE_WAIT 7
71 #if defined(DIAGNOSTIC)
74 #define LOCK_INLINE __inline
77 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
78 LK_SHARE_NONZERO | LK_WAIT_NONZERO)
80 static int acquire(struct lock *lkp, int extflags, int wanted);
82 static LOCK_INLINE void
83 sharelock(struct lock *lkp, int incr)
85 lkp->lk_flags |= LK_SHARE_NONZERO;
86 lkp->lk_sharecount += incr;
89 static LOCK_INLINE int
90 shareunlock(struct lock *lkp, int decr)
94 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
96 if (lkp->lk_sharecount == decr) {
97 lkp->lk_flags &= ~LK_SHARE_NONZERO;
98 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
101 lkp->lk_sharecount = 0;
103 lkp->lk_sharecount -= decr;
109 * lock acquisition helper routine. Called with the lock's spinlock held.
112 acquire(struct lock *lkp, int extflags, int wanted)
116 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
120 while ((lkp->lk_flags & wanted) != 0) {
121 lkp->lk_flags |= LK_WAIT_NONZERO;
125 * Atomic spinlock release/sleep/reacquire.
127 error = ssleep(lkp, &lkp->lk_spinlock,
128 ((extflags & LK_PCATCH) ? PCATCH : 0),
130 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
131 if (lkp->lk_waitcount == 1) {
132 lkp->lk_flags &= ~LK_WAIT_NONZERO;
133 lkp->lk_waitcount = 0;
139 if (extflags & LK_SLEEPFAIL)
146 * Set, change, or release a lock.
148 * Shared requests increment the shared count. Exclusive requests set the
149 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
150 * accepted shared locks and shared-to-exclusive upgrades to go away.
152 * A spinlock is held for most of the procedure. We must not do anything
153 * fancy while holding the spinlock.
157 lockmgr(struct lock *lkp, u_int flags)
159 debuglockmgr(struct lock *lkp, u_int flags,
160 const char *name, const char *file, int line)
174 if (mycpu->gd_intr_nesting_level &&
175 (flags & LK_NOWAIT) == 0 &&
176 (flags & LK_TYPE_MASK) != LK_RELEASE &&
177 panic_cpu_gd != mycpu
181 panic("lockmgr %s from %p: called from interrupt, ipi, "
182 "or hard code section",
183 lkp->lk_wmesg, ((int **)&lkp)[-1]);
185 panic("lockmgr %s from %s:%d: called from interrupt, ipi, "
186 "or hard code section",
187 lkp->lk_wmesg, file, line);
192 if (mycpu->gd_spinlocks && ((flags & LK_NOWAIT) == 0)) {
193 panic("lockmgr %s from %s:%d: called with %d spinlocks held",
194 lkp->lk_wmesg, file, line, mycpu->gd_spinlocks);
198 spin_lock(&lkp->lk_spinlock);
200 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
203 switch (flags & LK_TYPE_MASK) {
206 * If we are not the exclusive lock holder, we have to block
207 * while there is an exclusive lock holder or while an
208 * exclusive lock request or upgrade request is in progress.
210 * However, if TDF_DEADLKTREAT is set, we override exclusive
211 * lock requests or upgrade requests ( but not the exclusive
214 if (lkp->lk_lockholder != td) {
215 if (td->td_flags & TDF_DEADLKTREAT) {
225 LK_HAVE_EXCL | LK_WANT_EXCL |
237 * If we already hold an exclusive lock we bump the
238 * exclusive count instead of downgrading to a shared
241 * WARNING! The old FreeBSD behavior was to downgrade,
242 * but this creates a problem when recursions
243 * return to the caller and the caller expects
244 * its original exclusive lock to remain exclusively
247 if (extflags & LK_CANRECURSE) {
248 lkp->lk_exclusivecount++;
252 if (extflags & LK_NOWAIT) {
256 spin_unlock(&lkp->lk_spinlock);
257 panic("lockmgr: locking against myself");
260 * old code queued a shared lock request fell into
265 /* fall into downgrade */
269 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) {
270 spin_unlock(&lkp->lk_spinlock);
271 panic("lockmgr: not holding exclusive lock");
275 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
276 if (td->td_lockmgr_stack[i] == lkp &&
277 td->td_lockmgr_stack_id[i] > 0
279 td->td_lockmgr_stack_id[i]--;
285 sharelock(lkp, lkp->lk_exclusivecount);
286 lkp->lk_exclusivecount = 0;
287 lkp->lk_flags &= ~LK_HAVE_EXCL;
288 lkp->lk_lockholder = LK_NOTHREAD;
289 if (lkp->lk_waitcount)
295 * If another process is ahead of us to get an upgrade,
296 * then we want to fail rather than have an intervening
299 if (lkp->lk_flags & LK_WANT_UPGRADE) {
300 dowakeup = shareunlock(lkp, 1);
305 /* fall into normal upgrade */
309 * Upgrade a shared lock to an exclusive one. If another
310 * shared lock has already requested an upgrade to an
311 * exclusive lock, our shared lock is released and an
312 * exclusive lock is requested (which will be granted
313 * after the upgrade). If we return an error, the file
314 * will always be unlocked.
316 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) {
317 spin_unlock(&lkp->lk_spinlock);
318 panic("lockmgr: upgrade exclusive lock");
320 dowakeup += shareunlock(lkp, 1);
323 * If we are just polling, check to see if we will block.
325 if ((extflags & LK_NOWAIT) &&
326 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
327 lkp->lk_sharecount > 1)) {
331 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
333 * We are first shared lock to request an upgrade, so
334 * request upgrade and wait for the shared count to
335 * drop to zero, then take exclusive lock.
337 * Although I don't think this can occur for
338 * robustness we also wait for any exclusive locks
339 * to be released. LK_WANT_UPGRADE is supposed to
340 * prevent new exclusive locks but might not in the
343 lkp->lk_flags |= LK_WANT_UPGRADE;
344 error = acquire(lkp, extflags,
345 LK_HAVE_EXCL | LK_SHARE_NONZERO);
346 lkp->lk_flags &= ~LK_WANT_UPGRADE;
350 lkp->lk_flags |= LK_HAVE_EXCL;
351 lkp->lk_lockholder = td;
352 if (lkp->lk_exclusivecount != 0) {
353 spin_unlock(&lkp->lk_spinlock);
354 panic("lockmgr(1): non-zero exclusive count");
356 lkp->lk_exclusivecount = 1;
357 #if defined(DEBUG_LOCKS)
358 lkp->lk_filename = file;
359 lkp->lk_lineno = line;
360 lkp->lk_lockername = name;
362 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
364 * Recursive lockmgr path
366 if (td->td_lockmgr_stack[i] == lkp &&
367 td->td_lockmgr_stack_id[i] != 0
369 td->td_lockmgr_stack_id[i]++;
374 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
376 * Use new lockmgr tracking slot
378 if (td->td_lockmgr_stack_id[i] == 0) {
379 td->td_lockmgr_stack_id[i]++;
380 td->td_lockmgr_stack[i] = lkp;
391 * Someone else has requested upgrade. Release our shared
392 * lock, awaken upgrade requestor if we are the last shared
393 * lock, then request an exclusive lock.
395 if ((lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
399 /* fall into exclusive request */
402 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
406 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) {
407 spin_unlock(&lkp->lk_spinlock);
408 panic("lockmgr: locking against myself");
410 if ((extflags & LK_CANRECURSE) != 0) {
411 lkp->lk_exclusivecount++;
417 * If we are just polling, check to see if we will sleep.
419 if ((extflags & LK_NOWAIT) &&
420 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL |
421 LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
426 * Wait for exclusive lock holders to release and try to
427 * acquire the want_exclusive flag.
429 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
432 lkp->lk_flags |= LK_WANT_EXCL;
435 * Wait for shared locks and upgrades to finish. We can lose
436 * the race against a successful shared lock upgrade in which
437 * case LK_HAVE_EXCL will get set regardless of our
438 * acquisition of LK_WANT_EXCL, so we have to acquire
439 * LK_HAVE_EXCL here as well.
441 error = acquire(lkp, extflags, LK_HAVE_EXCL |
444 lkp->lk_flags &= ~LK_WANT_EXCL;
447 lkp->lk_flags |= LK_HAVE_EXCL;
448 lkp->lk_lockholder = td;
449 if (lkp->lk_exclusivecount != 0) {
450 spin_unlock(&lkp->lk_spinlock);
451 panic("lockmgr(2): non-zero exclusive count");
453 lkp->lk_exclusivecount = 1;
454 #if defined(DEBUG_LOCKS)
455 lkp->lk_filename = file;
456 lkp->lk_lineno = line;
457 lkp->lk_lockername = name;
459 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
461 * Recursive lockmgr path
463 if (td->td_lockmgr_stack[i] == lkp &&
464 td->td_lockmgr_stack_id[i] != 0
466 td->td_lockmgr_stack_id[i]++;
471 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
473 * Use new lockmgr tracking slot
475 if (td->td_lockmgr_stack_id[i] == 0) {
476 td->td_lockmgr_stack_id[i]++;
477 td->td_lockmgr_stack[i] = lkp;
488 if (lkp->lk_exclusivecount != 0) {
489 if (lkp->lk_lockholder != td &&
490 lkp->lk_lockholder != LK_KERNTHREAD) {
491 spin_unlock(&lkp->lk_spinlock);
492 panic("lockmgr: pid %d, not %s thr %p/%p unlocking",
493 (td->td_proc ? td->td_proc->p_pid : -1),
494 "exclusive lock holder",
495 td, lkp->lk_lockholder);
497 if (lkp->lk_lockholder != LK_KERNTHREAD) {
500 if (lkp->lk_exclusivecount == 1) {
501 lkp->lk_flags &= ~LK_HAVE_EXCL;
502 lkp->lk_lockholder = LK_NOTHREAD;
503 lkp->lk_exclusivecount = 0;
505 lkp->lk_exclusivecount--;
508 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
509 if (td->td_lockmgr_stack[i] == lkp &&
510 td->td_lockmgr_stack_id[i] > 0
512 td->td_lockmgr_stack_id[i]--;
513 lkp->lk_filename = file;
514 lkp->lk_lineno = line;
519 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
520 dowakeup += shareunlock(lkp, 1);
523 panic("lockmgr: LK_RELEASE: no lock held");
525 if (lkp->lk_flags & LK_WAIT_NONZERO)
530 spin_unlock(&lkp->lk_spinlock);
531 panic("lockmgr: unknown locktype request %d",
532 flags & LK_TYPE_MASK);
535 spin_unlock(&lkp->lk_spinlock);
542 lockmgr_kernproc(struct lock *lp)
544 struct thread *td __debugvar = curthread;
546 if (lp->lk_lockholder != LK_KERNTHREAD) {
547 KASSERT(lp->lk_lockholder == td,
548 ("lockmgr_kernproc: lock not owned by curthread %p", td));
550 lp->lk_lockholder = LK_KERNTHREAD;
556 * Set the lock to be exclusively held. The caller is holding the lock's
557 * spinlock and the spinlock remains held on return. A panic will occur
558 * if the lock cannot be set to exclusive.
560 * XXX not only unused but these functions also break EXCLUPGRADE's
564 lockmgr_setexclusive_interlocked(struct lock *lkp)
566 thread_t td = curthread;
568 KKASSERT((lkp->lk_flags & (LK_HAVE_EXCL|LK_SHARE_NONZERO)) == 0);
569 KKASSERT(lkp->lk_exclusivecount == 0);
570 lkp->lk_flags |= LK_HAVE_EXCL;
571 lkp->lk_lockholder = td;
572 lkp->lk_exclusivecount = 1;
577 * Clear the caller's exclusive lock. The caller is holding the lock's
578 * spinlock. THIS FUNCTION WILL UNLOCK THE SPINLOCK.
580 * A panic will occur if the caller does not hold the lock.
583 lockmgr_clrexclusive_interlocked(struct lock *lkp)
585 thread_t td __debugvar = curthread;
588 KKASSERT((lkp->lk_flags & LK_HAVE_EXCL) && lkp->lk_exclusivecount == 1
589 && lkp->lk_lockholder == td);
590 lkp->lk_lockholder = LK_NOTHREAD;
591 lkp->lk_flags &= ~LK_HAVE_EXCL;
592 lkp->lk_exclusivecount = 0;
593 if (lkp->lk_flags & LK_WAIT_NONZERO)
596 spin_unlock(&lkp->lk_spinlock);
604 * Initialize a lock; required before use.
607 lockinit(struct lock *lkp, const char *wmesg, int timo, int flags)
609 spin_init(&lkp->lk_spinlock);
610 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
611 lkp->lk_sharecount = 0;
612 lkp->lk_waitcount = 0;
613 lkp->lk_exclusivecount = 0;
614 lkp->lk_wmesg = wmesg;
616 lkp->lk_lockholder = LK_NOTHREAD;
620 * Reinitialize a lock that is being reused for a different purpose, but
621 * which may have pending (blocked) threads sitting on it. The caller
622 * must already hold the interlock.
625 lockreinit(struct lock *lkp, const char *wmesg, int timo, int flags)
627 spin_lock(&lkp->lk_spinlock);
628 lkp->lk_flags = (lkp->lk_flags & ~LK_EXTFLG_MASK) |
629 (flags & LK_EXTFLG_MASK);
630 lkp->lk_wmesg = wmesg;
632 spin_unlock(&lkp->lk_spinlock);
636 * Requires that the caller is the exclusive owner of this lock.
639 lockuninit(struct lock *l)
642 * At this point we should have removed all the references to this lock
643 * so there can't be anyone waiting on it.
645 KKASSERT(l->lk_waitcount == 0);
647 spin_uninit(&l->lk_spinlock);
651 * Determine the status of a lock.
654 lockstatus(struct lock *lkp, struct thread *td)
658 spin_lock(&lkp->lk_spinlock);
659 if (lkp->lk_exclusivecount != 0) {
660 if (td == NULL || lkp->lk_lockholder == td)
661 lock_type = LK_EXCLUSIVE;
663 lock_type = LK_EXCLOTHER;
664 } else if (lkp->lk_sharecount != 0) {
665 lock_type = LK_SHARED;
667 spin_unlock(&lkp->lk_spinlock);
672 * Return non-zero if the caller owns the lock shared or exclusive.
673 * We can only guess re: shared locks.
676 lockowned(struct lock *lkp)
678 thread_t td = curthread;
680 if (lkp->lk_exclusivecount)
681 return(lkp->lk_lockholder == td);
682 return(lkp->lk_sharecount != 0);
686 * Determine the number of holders of a lock.
688 * The non-blocking version can usually be used for assertions.
691 lockcount(struct lock *lkp)
695 spin_lock(&lkp->lk_spinlock);
696 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
697 spin_unlock(&lkp->lk_spinlock);
702 lockcountnb(struct lock *lkp)
704 return (lkp->lk_exclusivecount + lkp->lk_sharecount);
708 * Print out information about state of a lock. Used by VOP_PRINT
709 * routines to display status about contained locks.
712 lockmgr_printinfo(struct lock *lkp)
714 struct thread *td = lkp->lk_lockholder;
717 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
722 if (lkp->lk_sharecount)
723 kprintf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
725 else if (lkp->lk_flags & LK_HAVE_EXCL)
726 kprintf(" lock type %s: EXCL (count %d) by td %p pid %d",
727 lkp->lk_wmesg, lkp->lk_exclusivecount, td,
729 if (lkp->lk_waitcount > 0)
730 kprintf(" with %d pending", lkp->lk_waitcount);
734 lock_sysinit(struct lock_args *arg)
736 lockinit(arg->la_lock, arg->la_desc, 0, arg->la_flags);