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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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 1.3 2003/06/25 03:55:57 dillon Exp $
47 #include <sys/param.h>
50 #include <sys/systm.h>
53 * Locking primitives implementation.
54 * Locks provide shared/exclusive sychronization.
57 #ifdef SIMPLELOCK_DEBUG
58 #define COUNT(td, x) (td)->td_locks += (x)
63 #define LOCK_WAIT_TIME 100
64 #define LOCK_SAMPLE_WAIT 7
66 #if defined(DIAGNOSTIC)
69 #define LOCK_INLINE __inline
72 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
73 LK_SHARE_NONZERO | LK_WAIT_NONZERO)
75 static int acquire(struct lock *lkp, int extflags, int wanted);
76 static int apause(struct lock *lkp, int flags);
77 static int acquiredrain(struct lock *lkp, int extflags) ;
79 static LOCK_INLINE void
80 sharelock(struct lock *lkp, int incr) {
81 lkp->lk_flags |= LK_SHARE_NONZERO;
82 lkp->lk_sharecount += incr;
85 static LOCK_INLINE void
86 shareunlock(struct lock *lkp, int decr) {
88 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
90 if (lkp->lk_sharecount == decr) {
91 lkp->lk_flags &= ~LK_SHARE_NONZERO;
92 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
95 lkp->lk_sharecount = 0;
97 lkp->lk_sharecount -= decr;
102 * This is the waitloop optimization, and note for this to work
103 * simple_lock and simple_unlock should be subroutines to avoid
104 * optimization troubles.
107 apause(struct lock *lkp, int flags)
113 if ((lkp->lk_flags & flags) == 0)
116 for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) {
117 simple_unlock(&lkp->lk_interlock);
118 for (i = LOCK_SAMPLE_WAIT; i > 0; i--)
119 if ((lkp->lk_flags & flags) == 0)
121 simple_lock(&lkp->lk_interlock);
122 if ((lkp->lk_flags & flags) == 0)
130 acquire(struct lock *lkp, int extflags, int wanted) {
133 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
137 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
138 error = apause(lkp, wanted);
144 while ((lkp->lk_flags & wanted) != 0) {
145 lkp->lk_flags |= LK_WAIT_NONZERO;
147 simple_unlock(&lkp->lk_interlock);
148 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg,
149 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
150 simple_lock(&lkp->lk_interlock);
151 if (lkp->lk_waitcount == 1) {
152 lkp->lk_flags &= ~LK_WAIT_NONZERO;
153 lkp->lk_waitcount = 0;
161 if (extflags & LK_SLEEPFAIL) {
171 * Set, change, or release a lock.
173 * Shared requests increment the shared count. Exclusive requests set the
174 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
175 * accepted shared locks and shared-to-exclusive upgrades to go away.
179 lockmgr(struct lock *lkp, u_int flags, struct simplelock *interlkp,
182 debuglockmgr(struct lock *lkp, u_int flags, struct simplelock *interlkp,
183 struct thread *td, const char *name, const char *file, int line)
191 simple_lock(&lkp->lk_interlock);
192 if (flags & LK_INTERLOCK)
193 simple_unlock(interlkp);
195 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
197 switch (flags & LK_TYPE_MASK) {
201 * If we are not the exclusive lock holder, we have to block
202 * while there is an exclusive lock holder or while an
203 * exclusive lock request or upgrade request is in progress.
205 * However, if P_DEADLKTREAT is set, we override exclusive
206 * lock requests or upgrade requests ( but not the exclusive
209 if (lkp->lk_lockholder != td) {
210 if (td->td_flags & TDF_DEADLKTREAT) {
220 LK_HAVE_EXCL | LK_WANT_EXCL |
231 * We hold an exclusive lock, so downgrade it to shared.
232 * An alternative would be to fail with EDEADLK.
236 /* fall into downgrade */
239 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0)
240 panic("lockmgr: not holding exclusive lock");
241 sharelock(lkp, lkp->lk_exclusivecount);
242 lkp->lk_exclusivecount = 0;
243 lkp->lk_flags &= ~LK_HAVE_EXCL;
244 lkp->lk_lockholder = LK_NOTHREAD;
245 if (lkp->lk_waitcount)
251 * If another process is ahead of us to get an upgrade,
252 * then we want to fail rather than have an intervening
255 if (lkp->lk_flags & LK_WANT_UPGRADE) {
261 /* fall into normal upgrade */
265 * Upgrade a shared lock to an exclusive one. If another
266 * shared lock has already requested an upgrade to an
267 * exclusive lock, our shared lock is released and an
268 * exclusive lock is requested (which will be granted
269 * after the upgrade). If we return an error, the file
270 * will always be unlocked.
272 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0))
273 panic("lockmgr: upgrade exclusive lock");
277 * If we are just polling, check to see if we will block.
279 if ((extflags & LK_NOWAIT) &&
280 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
281 lkp->lk_sharecount > 1)) {
285 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
287 * We are first shared lock to request an upgrade, so
288 * request upgrade and wait for the shared count to
289 * drop to zero, then take exclusive lock.
291 lkp->lk_flags |= LK_WANT_UPGRADE;
292 error = acquire(lkp, extflags, LK_SHARE_NONZERO);
293 lkp->lk_flags &= ~LK_WANT_UPGRADE;
297 lkp->lk_flags |= LK_HAVE_EXCL;
298 lkp->lk_lockholder = td;
299 if (lkp->lk_exclusivecount != 0)
300 panic("lockmgr: non-zero exclusive count");
301 lkp->lk_exclusivecount = 1;
302 #if defined(DEBUG_LOCKS)
303 lkp->lk_filename = file;
304 lkp->lk_lineno = line;
305 lkp->lk_lockername = name;
311 * Someone else has requested upgrade. Release our shared
312 * lock, awaken upgrade requestor if we are the last shared
313 * lock, then request an exclusive lock.
315 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
318 /* fall into exclusive request */
321 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
325 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
326 panic("lockmgr: locking against myself");
327 if ((extflags & LK_CANRECURSE) != 0) {
328 lkp->lk_exclusivecount++;
334 * If we are just polling, check to see if we will sleep.
336 if ((extflags & LK_NOWAIT) &&
337 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
342 * Try to acquire the want_exclusive flag.
344 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
347 lkp->lk_flags |= LK_WANT_EXCL;
349 * Wait for shared locks and upgrades to finish.
351 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
352 lkp->lk_flags &= ~LK_WANT_EXCL;
355 lkp->lk_flags |= LK_HAVE_EXCL;
356 lkp->lk_lockholder = td;
357 if (lkp->lk_exclusivecount != 0)
358 panic("lockmgr: non-zero exclusive count");
359 lkp->lk_exclusivecount = 1;
360 #if defined(DEBUG_LOCKS)
361 lkp->lk_filename = file;
362 lkp->lk_lineno = line;
363 lkp->lk_lockername = name;
369 if (lkp->lk_exclusivecount != 0) {
370 if (lkp->lk_lockholder != td &&
371 lkp->lk_lockholder != LK_KERNTHREAD) {
372 panic("lockmgr: pid %d, not %s thr %p unlocking",
373 (td->td_proc ? td->td_proc->p_pid : -99),
374 "exclusive lock holder",
377 if (lkp->lk_lockholder != LK_KERNTHREAD) {
380 if (lkp->lk_exclusivecount == 1) {
381 lkp->lk_flags &= ~LK_HAVE_EXCL;
382 lkp->lk_lockholder = LK_NOTHREAD;
383 lkp->lk_exclusivecount = 0;
385 lkp->lk_exclusivecount--;
387 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
391 if (lkp->lk_flags & LK_WAIT_NONZERO)
397 * Check that we do not already hold the lock, as it can
398 * never drain if we do. Unfortunately, we have no way to
399 * check for holding a shared lock, but at least we can
400 * check for an exclusive one.
402 if (lkp->lk_lockholder == td)
403 panic("lockmgr: draining against myself");
405 error = acquiredrain(lkp, extflags);
408 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
409 lkp->lk_lockholder = td;
410 lkp->lk_exclusivecount = 1;
411 #if defined(DEBUG_LOCKS)
412 lkp->lk_filename = file;
413 lkp->lk_lineno = line;
414 lkp->lk_lockername = name;
420 simple_unlock(&lkp->lk_interlock);
421 panic("lockmgr: unknown locktype request %d",
422 flags & LK_TYPE_MASK);
425 if ((lkp->lk_flags & LK_WAITDRAIN) &&
426 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
427 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
428 lkp->lk_flags &= ~LK_WAITDRAIN;
429 wakeup((void *)&lkp->lk_flags);
431 simple_unlock(&lkp->lk_interlock);
436 acquiredrain(struct lock *lkp, int extflags) {
439 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
443 error = apause(lkp, LK_ALL);
447 while (lkp->lk_flags & LK_ALL) {
448 lkp->lk_flags |= LK_WAITDRAIN;
449 simple_unlock(&lkp->lk_interlock);
450 error = tsleep(&lkp->lk_flags, lkp->lk_prio,
452 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
453 simple_lock(&lkp->lk_interlock);
456 if (extflags & LK_SLEEPFAIL) {
464 * Initialize a lock; required before use.
467 lockinit(lkp, prio, wmesg, timo, flags)
475 simple_lock_init(&lkp->lk_interlock);
476 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
477 lkp->lk_sharecount = 0;
478 lkp->lk_waitcount = 0;
479 lkp->lk_exclusivecount = 0;
481 lkp->lk_wmesg = wmesg;
483 lkp->lk_lockholder = LK_NOTHREAD;
487 * Determine the status of a lock.
490 lockstatus(struct lock *lkp, struct thread *td)
494 simple_lock(&lkp->lk_interlock);
495 if (lkp->lk_exclusivecount != 0) {
496 if (td == NULL || lkp->lk_lockholder == td)
497 lock_type = LK_EXCLUSIVE;
499 lock_type = LK_EXCLOTHER;
500 } else if (lkp->lk_sharecount != 0)
501 lock_type = LK_SHARED;
502 simple_unlock(&lkp->lk_interlock);
507 * Determine the number of holders of a lock.
515 simple_lock(&lkp->lk_interlock);
516 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
517 simple_unlock(&lkp->lk_interlock);
522 * Print out information about state of a lock. Used by VOP_PRINT
523 * routines to display status about contained locks.
526 lockmgr_printinfo(lkp)
529 struct thread *td = lkp->lk_lockholder;
532 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
537 if (lkp->lk_sharecount)
538 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
540 else if (lkp->lk_flags & LK_HAVE_EXCL)
541 printf(" lock type %s: EXCL (count %d) by td %p pid %d",
542 lkp->lk_wmesg, lkp->lk_exclusivecount, td,
544 if (lkp->lk_waitcount > 0)
545 printf(" with %d pending", lkp->lk_waitcount);
548 #if defined(SIMPLELOCK_DEBUG) && (MAXCPU == 1 || defined(COMPILING_LINT))
549 #include <sys/kernel.h>
550 #include <sys/sysctl.h>
552 static int lockpausetime = 0;
553 SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, "");
555 static int simplelockrecurse;
558 * Simple lock functions so that the debugger can see from whence
559 * they are being called.
562 simple_lock_init(alp)
563 struct simplelock *alp;
570 _simple_lock(alp, id, l)
571 struct simplelock *alp;
576 if (simplelockrecurse)
578 if (alp->lock_data == 1) {
579 if (lockpausetime == -1)
580 panic("%s:%d: simple_lock: lock held", id, l);
581 printf("%s:%d: simple_lock: lock held\n", id, l);
582 if (lockpausetime == 1) {
583 Debugger("simple_lock");
584 /*BACKTRACE(curproc); */
585 } else if (lockpausetime > 1) {
586 printf("%s:%d: simple_lock: lock held...", id, l);
587 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock",
589 printf(" continuing\n");
594 curproc->p_simple_locks++;
598 _simple_lock_try(alp, id, l)
599 struct simplelock *alp;
606 if (simplelockrecurse)
610 curproc->p_simple_locks++;
615 _simple_unlock(alp, id, l)
616 struct simplelock *alp;
621 if (simplelockrecurse)
623 if (alp->lock_data == 0) {
624 if (lockpausetime == -1)
625 panic("%s:%d: simple_unlock: lock not held", id, l);
626 printf("%s:%d: simple_unlock: lock not held\n", id, l);
627 if (lockpausetime == 1) {
628 Debugger("simple_unlock");
629 /* BACKTRACE(curproc); */
630 } else if (lockpausetime > 1) {
631 printf("%s:%d: simple_unlock: lock not held...", id, l);
632 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock",
634 printf(" continuing\n");
639 curproc->p_simple_locks--;
641 #elif defined(SIMPLELOCK_DEBUG)
642 #error "SIMPLELOCK_DEBUG is not compatible with SMP!"
643 #endif /* SIMPLELOCK_DEBUG && MAXCPU == 1 */