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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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.
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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) {
84 lkp->lk_flags |= LK_SHARE_NONZERO;
85 lkp->lk_sharecount += incr;
88 static LOCK_INLINE int
89 shareunlock(struct lock *lkp, int decr)
93 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
95 if (lkp->lk_sharecount == decr) {
96 lkp->lk_flags &= ~LK_SHARE_NONZERO;
97 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
100 lkp->lk_sharecount = 0;
102 lkp->lk_sharecount -= decr;
108 * lock acquisition helper routine. Called with the lock's spinlock held.
111 acquire(struct lock *lkp, int extflags, int wanted)
115 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
119 while ((lkp->lk_flags & wanted) != 0) {
120 lkp->lk_flags |= LK_WAIT_NONZERO;
124 * Atomic spinlock release/sleep/reacquire.
126 error = ssleep(lkp, &lkp->lk_spinlock,
127 ((extflags & LK_PCATCH) ? PCATCH : 0),
129 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
130 if (lkp->lk_waitcount == 1) {
131 lkp->lk_flags &= ~LK_WAIT_NONZERO;
132 lkp->lk_waitcount = 0;
138 if (extflags & LK_SLEEPFAIL)
145 * Set, change, or release a lock.
147 * Shared requests increment the shared count. Exclusive requests set the
148 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
149 * accepted shared locks and shared-to-exclusive upgrades to go away.
151 * A spinlock is held for most of the procedure. We must not do anything
152 * fancy while holding the spinlock.
156 lockmgr(struct lock *lkp, u_int flags)
158 debuglockmgr(struct lock *lkp, u_int flags,
159 const char *name, const char *file, int line)
173 if (mycpu->gd_intr_nesting_level &&
174 (flags & LK_NOWAIT) == 0 &&
175 (flags & LK_TYPE_MASK) != LK_RELEASE &&
176 panic_cpu_gd != mycpu
180 panic("lockmgr %s from %p: called from interrupt, ipi, "
181 "or hard code section",
182 lkp->lk_wmesg, ((int **)&lkp)[-1]);
184 panic("lockmgr %s from %s:%d: called from interrupt, ipi, "
185 "or hard code section",
186 lkp->lk_wmesg, file, line);
191 if (mycpu->gd_spinlocks_wr &&
192 ((flags & LK_NOWAIT) == 0)
194 panic("lockmgr %s from %s:%d: called with %d spinlocks held",
195 lkp->lk_wmesg, file, line, mycpu->gd_spinlocks_wr);
200 * So sue me, I'm too tired.
202 if (spin_trylock(&lkp->lk_spinlock) == FALSE) {
203 if (flags & LK_NOSPINWAIT)
205 spin_lock(&lkp->lk_spinlock);
208 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
211 switch (flags & LK_TYPE_MASK) {
214 * If we are not the exclusive lock holder, we have to block
215 * while there is an exclusive lock holder or while an
216 * exclusive lock request or upgrade request is in progress.
218 * However, if TDF_DEADLKTREAT is set, we override exclusive
219 * lock requests or upgrade requests ( but not the exclusive
222 if (lkp->lk_lockholder != td) {
223 if (td->td_flags & TDF_DEADLKTREAT) {
233 LK_HAVE_EXCL | LK_WANT_EXCL |
244 * We hold an exclusive lock, so downgrade it to shared.
245 * An alternative would be to fail with EDEADLK.
249 /* fall into downgrade */
252 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) {
253 spin_unlock(&lkp->lk_spinlock);
254 panic("lockmgr: not holding exclusive lock");
258 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
259 if (td->td_lockmgr_stack[i] == lkp &&
260 td->td_lockmgr_stack_id[i] > 0
262 td->td_lockmgr_stack_id[i]--;
268 sharelock(lkp, lkp->lk_exclusivecount);
269 lkp->lk_exclusivecount = 0;
270 lkp->lk_flags &= ~LK_HAVE_EXCL;
271 lkp->lk_lockholder = LK_NOTHREAD;
272 if (lkp->lk_waitcount)
278 * If another process is ahead of us to get an upgrade,
279 * then we want to fail rather than have an intervening
282 if (lkp->lk_flags & LK_WANT_UPGRADE) {
283 dowakeup = shareunlock(lkp, 1);
288 /* fall into normal upgrade */
292 * Upgrade a shared lock to an exclusive one. If another
293 * shared lock has already requested an upgrade to an
294 * exclusive lock, our shared lock is released and an
295 * exclusive lock is requested (which will be granted
296 * after the upgrade). If we return an error, the file
297 * will always be unlocked.
299 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) {
300 spin_unlock(&lkp->lk_spinlock);
301 panic("lockmgr: upgrade exclusive lock");
303 dowakeup += shareunlock(lkp, 1);
306 * If we are just polling, check to see if we will block.
308 if ((extflags & LK_NOWAIT) &&
309 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
310 lkp->lk_sharecount > 1)) {
314 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
316 * We are first shared lock to request an upgrade, so
317 * request upgrade and wait for the shared count to
318 * drop to zero, then take exclusive lock.
320 * Although I don't think this can occur for
321 * robustness we also wait for any exclusive locks
322 * to be released. LK_WANT_UPGRADE is supposed to
323 * prevent new exclusive locks but might not in the
326 lkp->lk_flags |= LK_WANT_UPGRADE;
327 error = acquire(lkp, extflags,
328 LK_HAVE_EXCL | LK_SHARE_NONZERO);
329 lkp->lk_flags &= ~LK_WANT_UPGRADE;
333 lkp->lk_flags |= LK_HAVE_EXCL;
334 lkp->lk_lockholder = td;
335 if (lkp->lk_exclusivecount != 0) {
336 spin_unlock(&lkp->lk_spinlock);
337 panic("lockmgr(1): non-zero exclusive count");
339 lkp->lk_exclusivecount = 1;
340 #if defined(DEBUG_LOCKS)
341 lkp->lk_filename = file;
342 lkp->lk_lineno = line;
343 lkp->lk_lockername = name;
345 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
347 * Recursive lockmgr path
349 if (td->td_lockmgr_stack[i] == lkp &&
350 td->td_lockmgr_stack_id[i] != 0
352 td->td_lockmgr_stack_id[i]++;
357 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
359 * Use new lockmgr tracking slot
361 if (td->td_lockmgr_stack_id[i] == 0) {
362 td->td_lockmgr_stack_id[i]++;
363 td->td_lockmgr_stack[i] = lkp;
374 * Someone else has requested upgrade. Release our shared
375 * lock, awaken upgrade requestor if we are the last shared
376 * lock, then request an exclusive lock.
378 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
382 /* fall into exclusive request */
385 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
389 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) {
390 spin_unlock(&lkp->lk_spinlock);
391 panic("lockmgr: locking against myself");
393 if ((extflags & LK_CANRECURSE) != 0) {
394 lkp->lk_exclusivecount++;
400 * If we are just polling, check to see if we will sleep.
402 if ((extflags & LK_NOWAIT) &&
403 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL |
404 LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
409 * Wait for exclusive lock holders to release and try to
410 * acquire the want_exclusive flag.
412 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
415 lkp->lk_flags |= LK_WANT_EXCL;
418 * Wait for shared locks and upgrades to finish. We can lose
419 * the race against a successful shared lock upgrade in which
420 * case LK_HAVE_EXCL will get set regardless of our
421 * acquisition of LK_WANT_EXCL, so we have to acquire
422 * LK_HAVE_EXCL here as well.
424 error = acquire(lkp, extflags, LK_HAVE_EXCL |
427 lkp->lk_flags &= ~LK_WANT_EXCL;
430 lkp->lk_flags |= LK_HAVE_EXCL;
431 lkp->lk_lockholder = td;
432 if (lkp->lk_exclusivecount != 0) {
433 spin_unlock(&lkp->lk_spinlock);
434 panic("lockmgr(2): non-zero exclusive count");
436 lkp->lk_exclusivecount = 1;
437 #if defined(DEBUG_LOCKS)
438 lkp->lk_filename = file;
439 lkp->lk_lineno = line;
440 lkp->lk_lockername = name;
442 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
444 * Recursive lockmgr path
446 if (td->td_lockmgr_stack[i] == lkp &&
447 td->td_lockmgr_stack_id[i] != 0
449 td->td_lockmgr_stack_id[i]++;
454 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
456 * Use new lockmgr tracking slot
458 if (td->td_lockmgr_stack_id[i] == 0) {
459 td->td_lockmgr_stack_id[i]++;
460 td->td_lockmgr_stack[i] = lkp;
471 if (lkp->lk_exclusivecount != 0) {
472 if (lkp->lk_lockholder != td &&
473 lkp->lk_lockholder != LK_KERNTHREAD) {
474 spin_unlock(&lkp->lk_spinlock);
475 panic("lockmgr: pid %d, not %s thr %p/%p unlocking",
476 (td->td_proc ? td->td_proc->p_pid : -1),
477 "exclusive lock holder",
478 td, lkp->lk_lockholder);
480 if (lkp->lk_lockholder != LK_KERNTHREAD) {
483 if (lkp->lk_exclusivecount == 1) {
484 lkp->lk_flags &= ~LK_HAVE_EXCL;
485 lkp->lk_lockholder = LK_NOTHREAD;
486 lkp->lk_exclusivecount = 0;
488 lkp->lk_exclusivecount--;
491 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
492 if (td->td_lockmgr_stack[i] == lkp &&
493 td->td_lockmgr_stack_id[i] > 0
495 td->td_lockmgr_stack_id[i]--;
500 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
501 dowakeup += shareunlock(lkp, 1);
504 if (lkp->lk_flags & LK_WAIT_NONZERO)
509 spin_unlock(&lkp->lk_spinlock);
510 panic("lockmgr: unknown locktype request %d",
511 flags & LK_TYPE_MASK);
514 spin_unlock(&lkp->lk_spinlock);
521 lockmgr_kernproc(struct lock *lp)
523 struct thread *td __debugvar = curthread;
525 if (lp->lk_lockholder != LK_KERNTHREAD) {
526 KASSERT(lp->lk_lockholder == td,
527 ("lockmgr_kernproc: lock not owned by curthread %p", td));
529 lp->lk_lockholder = LK_KERNTHREAD;
535 * Set the lock to be exclusively held. The caller is holding the lock's
536 * spinlock and the spinlock remains held on return. A panic will occur
537 * if the lock cannot be set to exclusive.
540 lockmgr_setexclusive_interlocked(struct lock *lkp)
542 thread_t td = curthread;
544 KKASSERT((lkp->lk_flags & (LK_HAVE_EXCL|LK_SHARE_NONZERO)) == 0);
545 KKASSERT(lkp->lk_exclusivecount == 0);
546 lkp->lk_flags |= LK_HAVE_EXCL;
547 lkp->lk_lockholder = td;
548 lkp->lk_exclusivecount = 1;
553 * Clear the caller's exclusive lock. The caller is holding the lock's
554 * spinlock. THIS FUNCTION WILL UNLOCK THE SPINLOCK.
556 * A panic will occur if the caller does not hold the lock.
559 lockmgr_clrexclusive_interlocked(struct lock *lkp)
561 thread_t td __debugvar = curthread;
564 KKASSERT((lkp->lk_flags & LK_HAVE_EXCL) && lkp->lk_exclusivecount == 1
565 && lkp->lk_lockholder == td);
566 lkp->lk_lockholder = LK_NOTHREAD;
567 lkp->lk_flags &= ~LK_HAVE_EXCL;
568 lkp->lk_exclusivecount = 0;
569 if (lkp->lk_flags & LK_WAIT_NONZERO)
572 spin_unlock(&lkp->lk_spinlock);
580 * Initialize a lock; required before use.
583 lockinit(struct lock *lkp, char *wmesg, int timo, int flags)
585 spin_init(&lkp->lk_spinlock);
586 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
587 lkp->lk_sharecount = 0;
588 lkp->lk_waitcount = 0;
589 lkp->lk_exclusivecount = 0;
590 lkp->lk_wmesg = wmesg;
592 lkp->lk_lockholder = LK_NOTHREAD;
596 * Reinitialize a lock that is being reused for a different purpose, but
597 * which may have pending (blocked) threads sitting on it. The caller
598 * must already hold the interlock.
601 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags)
603 spin_lock(&lkp->lk_spinlock);
604 lkp->lk_flags = (lkp->lk_flags & ~LK_EXTFLG_MASK) |
605 (flags & LK_EXTFLG_MASK);
606 lkp->lk_wmesg = wmesg;
608 spin_unlock(&lkp->lk_spinlock);
612 * Requires that the caller is the exclusive owner of this lock.
615 lockuninit(struct lock *l)
618 * At this point we should have removed all the references to this lock
619 * so there can't be anyone waiting on it.
621 KKASSERT(l->lk_waitcount == 0);
623 spin_uninit(&l->lk_spinlock);
627 * Determine the status of a lock.
630 lockstatus(struct lock *lkp, struct thread *td)
634 spin_lock(&lkp->lk_spinlock);
635 if (lkp->lk_exclusivecount != 0) {
636 if (td == NULL || lkp->lk_lockholder == td)
637 lock_type = LK_EXCLUSIVE;
639 lock_type = LK_EXCLOTHER;
640 } else if (lkp->lk_sharecount != 0) {
641 lock_type = LK_SHARED;
643 spin_unlock(&lkp->lk_spinlock);
648 * Return non-zero if the caller owns the lock shared or exclusive.
649 * We can only guess re: shared locks.
652 lockowned(struct lock *lkp)
654 thread_t td = curthread;
656 if (lkp->lk_exclusivecount)
657 return(lkp->lk_lockholder == td);
658 return(lkp->lk_sharecount != 0);
662 * Determine the number of holders of a lock.
664 * The non-blocking version can usually be used for assertions.
667 lockcount(struct lock *lkp)
671 spin_lock(&lkp->lk_spinlock);
672 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
673 spin_unlock(&lkp->lk_spinlock);
678 lockcountnb(struct lock *lkp)
680 return (lkp->lk_exclusivecount + lkp->lk_sharecount);
684 * Print out information about state of a lock. Used by VOP_PRINT
685 * routines to display status about contained locks.
688 lockmgr_printinfo(struct lock *lkp)
690 struct thread *td = lkp->lk_lockholder;
693 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
698 if (lkp->lk_sharecount)
699 kprintf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
701 else if (lkp->lk_flags & LK_HAVE_EXCL)
702 kprintf(" lock type %s: EXCL (count %d) by td %p pid %d",
703 lkp->lk_wmesg, lkp->lk_exclusivecount, td,
705 if (lkp->lk_waitcount > 0)
706 kprintf(" with %d pending", lkp->lk_waitcount);