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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16 * notice, this list of conditions and the following disclaimer.
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19 * documentation and/or other materials provided with the distribution.
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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 1.14 2005/06/06 15:02:27 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/thread2.h>
56 * 0: no warnings, 1: warnings, 2: panic
58 static int lockmgr_from_int = 1;
59 SYSCTL_INT(_debug, OID_AUTO, lockmgr_from_int, CTLFLAG_RW, &lockmgr_from_int, 0, "");
62 * Locking primitives implementation.
63 * Locks provide shared/exclusive sychronization.
66 #ifdef SIMPLELOCK_DEBUG
67 #define COUNT(td, x) (td)->td_locks += (x)
72 #define LOCK_WAIT_TIME 100
73 #define LOCK_SAMPLE_WAIT 7
75 #if defined(DIAGNOSTIC)
78 #define LOCK_INLINE __inline
81 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
82 LK_SHARE_NONZERO | LK_WAIT_NONZERO)
84 static int acquire(struct lock *lkp, int extflags, int wanted);
85 static int acquiredrain(struct lock *lkp, int extflags) ;
87 static LOCK_INLINE void
88 sharelock(struct lock *lkp, int incr) {
89 lkp->lk_flags |= LK_SHARE_NONZERO;
90 lkp->lk_sharecount += incr;
93 static LOCK_INLINE void
94 shareunlock(struct lock *lkp, int decr) {
96 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
98 if (lkp->lk_sharecount == decr) {
99 lkp->lk_flags &= ~LK_SHARE_NONZERO;
100 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
103 lkp->lk_sharecount = 0;
105 lkp->lk_sharecount -= decr;
110 acquire(struct lock *lkp, int extflags, int wanted)
114 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
118 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
119 if ((lkp->lk_flags & wanted) == 0)
124 while ((lkp->lk_flags & wanted) != 0) {
125 lkp->lk_flags |= LK_WAIT_NONZERO;
127 /* note: serialization lock is held through tsleep */
128 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg,
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;
140 if (extflags & LK_SLEEPFAIL) {
150 * Set, change, or release a lock.
152 * Shared requests increment the shared count. Exclusive requests set the
153 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
154 * accepted shared locks and shared-to-exclusive upgrades to go away.
158 lockmgr(struct lock *lkp, u_int flags, lwkt_tokref_t interlkp,
161 debuglockmgr(struct lock *lkp, u_int flags, lwkt_tokref_t interlkp,
162 struct thread *td, const char *name, const char *file, int line)
172 if (lockmgr_from_int && mycpu->gd_intr_nesting_level &&
173 (flags & LK_NOWAIT) == 0 &&
174 (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) {
176 if (lockmgr_from_int == 2) {
179 "lockmgr %s from %p: called from interrupt",
180 lkp->lk_wmesg, ((int **)&lkp)[-1]);
184 "lockmgr %s from %p: called from interrupt\n",
185 lkp->lk_wmesg, ((int **)&lkp)[-1]);
188 if (lockmgr_from_int == 2) {
191 "lockmgr %s from %s:%d: called from interrupt",
192 lkp->lk_wmesg, file, line);
196 "lockmgr %s from %s:%d: called from interrupt\n",
197 lkp->lk_wmesg, file, line);
202 lwkt_gettoken(&ilock, &lkp->lk_interlock);
203 if (flags & LK_INTERLOCK)
204 lwkt_reltoken(interlkp);
206 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
208 switch (flags & LK_TYPE_MASK) {
212 * If we are not the exclusive lock holder, we have to block
213 * while there is an exclusive lock holder or while an
214 * exclusive lock request or upgrade request is in progress.
216 * However, if P_DEADLKTREAT is set, we override exclusive
217 * lock requests or upgrade requests ( but not the exclusive
220 if (lkp->lk_lockholder != td) {
221 if (td->td_flags & TDF_DEADLKTREAT) {
231 LK_HAVE_EXCL | LK_WANT_EXCL |
242 * We hold an exclusive lock, so downgrade it to shared.
243 * An alternative would be to fail with EDEADLK.
247 /* fall into downgrade */
250 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0)
251 panic("lockmgr: not holding exclusive lock");
252 sharelock(lkp, lkp->lk_exclusivecount);
253 lkp->lk_exclusivecount = 0;
254 lkp->lk_flags &= ~LK_HAVE_EXCL;
255 lkp->lk_lockholder = LK_NOTHREAD;
256 if (lkp->lk_waitcount)
262 * If another process is ahead of us to get an upgrade,
263 * then we want to fail rather than have an intervening
266 if (lkp->lk_flags & LK_WANT_UPGRADE) {
272 /* fall into normal upgrade */
276 * Upgrade a shared lock to an exclusive one. If another
277 * shared lock has already requested an upgrade to an
278 * exclusive lock, our shared lock is released and an
279 * exclusive lock is requested (which will be granted
280 * after the upgrade). If we return an error, the file
281 * will always be unlocked.
283 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0))
284 panic("lockmgr: upgrade exclusive lock");
288 * If we are just polling, check to see if we will block.
290 if ((extflags & LK_NOWAIT) &&
291 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
292 lkp->lk_sharecount > 1)) {
296 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
298 * We are first shared lock to request an upgrade, so
299 * request upgrade and wait for the shared count to
300 * drop to zero, then take exclusive lock.
302 lkp->lk_flags |= LK_WANT_UPGRADE;
303 error = acquire(lkp, extflags, LK_SHARE_NONZERO);
304 lkp->lk_flags &= ~LK_WANT_UPGRADE;
308 lkp->lk_flags |= LK_HAVE_EXCL;
309 lkp->lk_lockholder = td;
310 if (lkp->lk_exclusivecount != 0)
311 panic("lockmgr: non-zero exclusive count");
312 lkp->lk_exclusivecount = 1;
313 #if defined(DEBUG_LOCKS)
314 lkp->lk_filename = file;
315 lkp->lk_lineno = line;
316 lkp->lk_lockername = name;
322 * Someone else has requested upgrade. Release our shared
323 * lock, awaken upgrade requestor if we are the last shared
324 * lock, then request an exclusive lock.
326 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
329 /* fall into exclusive request */
332 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
336 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
337 panic("lockmgr: locking against myself");
338 if ((extflags & LK_CANRECURSE) != 0) {
339 lkp->lk_exclusivecount++;
345 * If we are just polling, check to see if we will sleep.
347 if ((extflags & LK_NOWAIT) &&
348 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
353 * Try to acquire the want_exclusive flag.
355 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
358 lkp->lk_flags |= LK_WANT_EXCL;
360 * Wait for shared locks and upgrades to finish.
362 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
363 lkp->lk_flags &= ~LK_WANT_EXCL;
366 lkp->lk_flags |= LK_HAVE_EXCL;
367 lkp->lk_lockholder = td;
368 if (lkp->lk_exclusivecount != 0)
369 panic("lockmgr: non-zero exclusive count");
370 lkp->lk_exclusivecount = 1;
371 #if defined(DEBUG_LOCKS)
372 lkp->lk_filename = file;
373 lkp->lk_lineno = line;
374 lkp->lk_lockername = name;
380 if (lkp->lk_exclusivecount != 0) {
381 if (lkp->lk_lockholder != td &&
382 lkp->lk_lockholder != LK_KERNTHREAD) {
383 panic("lockmgr: pid %d, not %s thr %p unlocking",
384 (td->td_proc ? td->td_proc->p_pid : -99),
385 "exclusive lock holder",
388 if (lkp->lk_lockholder != LK_KERNTHREAD) {
391 if (lkp->lk_exclusivecount == 1) {
392 lkp->lk_flags &= ~LK_HAVE_EXCL;
393 lkp->lk_lockholder = LK_NOTHREAD;
394 lkp->lk_exclusivecount = 0;
396 lkp->lk_exclusivecount--;
398 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
402 if (lkp->lk_flags & LK_WAIT_NONZERO)
408 * Check that we do not already hold the lock, as it can
409 * never drain if we do. Unfortunately, we have no way to
410 * check for holding a shared lock, but at least we can
411 * check for an exclusive one.
413 if (lkp->lk_lockholder == td)
414 panic("lockmgr: draining against myself");
416 error = acquiredrain(lkp, extflags);
419 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
420 lkp->lk_lockholder = td;
421 lkp->lk_exclusivecount = 1;
422 #if defined(DEBUG_LOCKS)
423 lkp->lk_filename = file;
424 lkp->lk_lineno = line;
425 lkp->lk_lockername = name;
431 lwkt_reltoken(&ilock);
432 panic("lockmgr: unknown locktype request %d",
433 flags & LK_TYPE_MASK);
436 if ((lkp->lk_flags & LK_WAITDRAIN) &&
437 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
438 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
439 lkp->lk_flags &= ~LK_WAITDRAIN;
440 wakeup((void *)&lkp->lk_flags);
442 lwkt_reltoken(&ilock);
447 acquiredrain(struct lock *lkp, int extflags)
451 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
455 if ((lkp->lk_flags & LK_ALL) == 0)
458 while (lkp->lk_flags & LK_ALL) {
459 lkp->lk_flags |= LK_WAITDRAIN;
460 /* interlock serialization held through tsleep */
461 error = tsleep(&lkp->lk_flags, lkp->lk_prio,
463 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
466 if (extflags & LK_SLEEPFAIL) {
474 * Initialize a lock; required before use.
477 lockinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags)
479 lwkt_token_init(&lkp->lk_interlock);
480 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
481 lkp->lk_sharecount = 0;
482 lkp->lk_waitcount = 0;
483 lkp->lk_exclusivecount = 0;
485 lkp->lk_wmesg = wmesg;
487 lkp->lk_lockholder = LK_NOTHREAD;
491 * Reinitialize a lock that is being reused for a different purpose, but
492 * which may have pending (blocked) threads sitting on it. The caller
493 * must already hold the interlock.
496 lockreinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags)
498 lkp->lk_flags = (lkp->lk_flags & ~(LK_EXTFLG_MASK|LK_DRAINING)) |
499 (flags & LK_EXTFLG_MASK);
501 lkp->lk_wmesg = wmesg;
506 * Determine the status of a lock.
509 lockstatus(struct lock *lkp, struct thread *td)
514 lwkt_gettoken(&ilock, &lkp->lk_interlock);
515 if (lkp->lk_exclusivecount != 0) {
516 if (td == NULL || lkp->lk_lockholder == td)
517 lock_type = LK_EXCLUSIVE;
519 lock_type = LK_EXCLOTHER;
520 } else if (lkp->lk_sharecount != 0) {
521 lock_type = LK_SHARED;
523 lwkt_reltoken(&ilock);
528 * Determine the number of holders of a lock.
530 * The non-blocking version can usually be used for assertions.
533 lockcount(struct lock *lkp)
538 lwkt_gettoken(&ilock, &lkp->lk_interlock);
539 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
540 lwkt_reltoken(&ilock);
545 lockcountnb(struct lock *lkp)
547 return (lkp->lk_exclusivecount + lkp->lk_sharecount);
551 * Print out information about state of a lock. Used by VOP_PRINT
552 * routines to display status about contained locks.
555 lockmgr_printinfo(struct lock *lkp)
557 struct thread *td = lkp->lk_lockholder;
560 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
565 if (lkp->lk_sharecount)
566 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
568 else if (lkp->lk_flags & LK_HAVE_EXCL)
569 printf(" lock type %s: EXCL (count %d) by td %p pid %d",
570 lkp->lk_wmesg, lkp->lk_exclusivecount, td,
572 if (lkp->lk_waitcount > 0)
573 printf(" with %d pending", lkp->lk_waitcount);