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.
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. 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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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 1.17 2006/04/23 02:41:12 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);
88 static LOCK_INLINE void
89 sharelock(struct lock *lkp, int incr) {
90 lkp->lk_flags |= LK_SHARE_NONZERO;
91 lkp->lk_sharecount += incr;
94 static LOCK_INLINE void
95 shareunlock(struct lock *lkp, int decr) {
97 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
99 if (lkp->lk_sharecount == decr) {
100 lkp->lk_flags &= ~LK_SHARE_NONZERO;
101 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
104 lkp->lk_sharecount = 0;
106 lkp->lk_sharecount -= decr;
111 * lock acquisition helper routine. Called with the lock's spinlock held.
114 acquire(struct lock *lkp, int extflags, int wanted)
118 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
122 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
123 if ((lkp->lk_flags & wanted) == 0)
127 while ((lkp->lk_flags & wanted) != 0) {
128 lkp->lk_flags |= LK_WAIT_NONZERO;
132 * Use the _quick version so the critical section is left
133 * intact, protecting the tsleep interlock. See
134 * tsleep_interlock() for a description of what is
137 tsleep_interlock(lkp);
138 spin_unlock_quick(&lkp->lk_spinlock);
140 ((extflags & LK_PCATCH) ? PCATCH : 0),
142 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
143 spin_lock_quick(&lkp->lk_spinlock);
144 if (lkp->lk_waitcount == 1) {
145 lkp->lk_flags &= ~LK_WAIT_NONZERO;
146 lkp->lk_waitcount = 0;
152 if (extflags & LK_SLEEPFAIL)
159 * Set, change, or release a lock.
161 * Shared requests increment the shared count. Exclusive requests set the
162 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
163 * accepted shared locks and shared-to-exclusive upgrades to go away.
165 * A spinlock is held for most of the procedure. We must not do anything
166 * fancy while holding the spinlock.
170 lockmgr(struct lock *lkp, u_int flags, struct spinlock *interlkp,
173 debuglockmgr(struct lock *lkp, u_int flags, struct spinlock *interlkp,
174 struct thread *td, const char *name, const char *file, int line)
183 if (lockmgr_from_int && mycpu->gd_intr_nesting_level &&
184 (flags & LK_NOWAIT) == 0 &&
185 (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) {
187 if (lockmgr_from_int == 2) {
189 if (flags & LK_INTERLOCK)
190 spin_unlock(interlkp);
192 "lockmgr %s from %p: called from interrupt",
193 lkp->lk_wmesg, ((int **)&lkp)[-1]);
197 "lockmgr %s from %p: called from interrupt\n",
198 lkp->lk_wmesg, ((int **)&lkp)[-1]);
201 if (lockmgr_from_int == 2) {
203 if (flags & LK_INTERLOCK)
204 spin_unlock(interlkp);
206 "lockmgr %s from %s:%d: called from interrupt",
207 lkp->lk_wmesg, file, line);
211 "lockmgr %s from %s:%d: called from interrupt\n",
212 lkp->lk_wmesg, file, line);
217 spin_lock(&lkp->lk_spinlock);
218 if (flags & LK_INTERLOCK)
219 spin_unlock(interlkp);
221 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
223 switch (flags & LK_TYPE_MASK) {
226 * If we are not the exclusive lock holder, we have to block
227 * while there is an exclusive lock holder or while an
228 * exclusive lock request or upgrade request is in progress.
230 * However, if P_DEADLKTREAT is set, we override exclusive
231 * lock requests or upgrade requests ( but not the exclusive
234 if (lkp->lk_lockholder != td) {
235 if (td->td_flags & TDF_DEADLKTREAT) {
245 LK_HAVE_EXCL | LK_WANT_EXCL |
256 * We hold an exclusive lock, so downgrade it to shared.
257 * An alternative would be to fail with EDEADLK.
261 /* fall into downgrade */
264 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) {
265 spin_unlock(&lkp->lk_spinlock);
266 panic("lockmgr: not holding exclusive lock");
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) {
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");
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 lkp->lk_flags |= LK_WANT_UPGRADE;
321 error = acquire(lkp, extflags, LK_SHARE_NONZERO);
322 lkp->lk_flags &= ~LK_WANT_UPGRADE;
326 lkp->lk_flags |= LK_HAVE_EXCL;
327 lkp->lk_lockholder = td;
328 if (lkp->lk_exclusivecount != 0) {
329 spin_unlock(&lkp->lk_spinlock);
330 panic("lockmgr: non-zero exclusive count");
332 lkp->lk_exclusivecount = 1;
333 #if defined(DEBUG_LOCKS)
334 lkp->lk_filename = file;
335 lkp->lk_lineno = line;
336 lkp->lk_lockername = name;
342 * Someone else has requested upgrade. Release our shared
343 * lock, awaken upgrade requestor if we are the last shared
344 * lock, then request an exclusive lock.
346 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
349 /* fall into exclusive request */
352 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
356 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) {
357 spin_unlock(&lkp->lk_spinlock);
358 panic("lockmgr: locking against myself");
360 if ((extflags & LK_CANRECURSE) != 0) {
361 lkp->lk_exclusivecount++;
367 * If we are just polling, check to see if we will sleep.
369 if ((extflags & LK_NOWAIT) &&
370 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
375 * Try to acquire the want_exclusive flag.
377 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
380 lkp->lk_flags |= LK_WANT_EXCL;
382 * Wait for shared locks and upgrades to finish.
384 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
385 lkp->lk_flags &= ~LK_WANT_EXCL;
388 lkp->lk_flags |= LK_HAVE_EXCL;
389 lkp->lk_lockholder = td;
390 if (lkp->lk_exclusivecount != 0) {
391 spin_unlock(&lkp->lk_spinlock);
392 panic("lockmgr: non-zero exclusive count");
394 lkp->lk_exclusivecount = 1;
395 #if defined(DEBUG_LOCKS)
396 lkp->lk_filename = file;
397 lkp->lk_lineno = line;
398 lkp->lk_lockername = name;
404 if (lkp->lk_exclusivecount != 0) {
405 if (lkp->lk_lockholder != td &&
406 lkp->lk_lockholder != LK_KERNTHREAD) {
407 spin_unlock(&lkp->lk_spinlock);
408 panic("lockmgr: pid %d, not %s thr %p unlocking",
409 (td->td_proc ? td->td_proc->p_pid : -99),
410 "exclusive lock holder",
413 if (lkp->lk_lockholder != LK_KERNTHREAD) {
416 if (lkp->lk_exclusivecount == 1) {
417 lkp->lk_flags &= ~LK_HAVE_EXCL;
418 lkp->lk_lockholder = LK_NOTHREAD;
419 lkp->lk_exclusivecount = 0;
421 lkp->lk_exclusivecount--;
423 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
427 if (lkp->lk_flags & LK_WAIT_NONZERO)
432 spin_unlock(&lkp->lk_spinlock);
433 panic("lockmgr: unknown locktype request %d",
434 flags & LK_TYPE_MASK);
437 spin_unlock(&lkp->lk_spinlock);
442 * Initialize a lock; required before use.
445 lockinit(struct lock *lkp, char *wmesg, int timo, int flags)
447 spin_init(&lkp->lk_spinlock);
448 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
449 lkp->lk_sharecount = 0;
450 lkp->lk_waitcount = 0;
451 lkp->lk_exclusivecount = 0;
452 lkp->lk_wmesg = wmesg;
454 lkp->lk_lockholder = LK_NOTHREAD;
458 * Reinitialize a lock that is being reused for a different purpose, but
459 * which may have pending (blocked) threads sitting on it. The caller
460 * must already hold the interlock.
463 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags)
465 lkp->lk_flags = (lkp->lk_flags & ~LK_EXTFLG_MASK) |
466 (flags & LK_EXTFLG_MASK);
467 lkp->lk_wmesg = wmesg;
472 * Determine the status of a lock.
475 lockstatus(struct lock *lkp, struct thread *td)
479 spin_lock(&lkp->lk_spinlock);
480 if (lkp->lk_exclusivecount != 0) {
481 if (td == NULL || lkp->lk_lockholder == td)
482 lock_type = LK_EXCLUSIVE;
484 lock_type = LK_EXCLOTHER;
485 } else if (lkp->lk_sharecount != 0) {
486 lock_type = LK_SHARED;
488 spin_unlock(&lkp->lk_spinlock);
493 * Determine the number of holders of a lock.
495 * The non-blocking version can usually be used for assertions.
498 lockcount(struct lock *lkp)
502 spin_lock(&lkp->lk_spinlock);
503 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
504 spin_unlock(&lkp->lk_spinlock);
509 lockcountnb(struct lock *lkp)
511 return (lkp->lk_exclusivecount + lkp->lk_sharecount);
515 * Print out information about state of a lock. Used by VOP_PRINT
516 * routines to display status about contained locks.
519 lockmgr_printinfo(struct lock *lkp)
521 struct thread *td = lkp->lk_lockholder;
524 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
529 if (lkp->lk_sharecount)
530 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
532 else if (lkp->lk_flags & LK_HAVE_EXCL)
533 printf(" lock type %s: EXCL (count %d) by td %p pid %d",
534 lkp->lk_wmesg, lkp->lk_exclusivecount, td,
536 if (lkp->lk_waitcount > 0)
537 printf(" with %d pending", lkp->lk_waitcount);