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 $
46 #include <sys/param.h>
49 #include <sys/systm.h>
52 * Locking primitives implementation.
53 * Locks provide shared/exclusive sychronization.
56 #ifdef SIMPLELOCK_DEBUG
57 #define COUNT(p, x) if (p) (p)->p_locks += (x)
62 #define LOCK_WAIT_TIME 100
63 #define LOCK_SAMPLE_WAIT 7
65 #if defined(DIAGNOSTIC)
68 #define LOCK_INLINE __inline
71 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
72 LK_SHARE_NONZERO | LK_WAIT_NONZERO)
74 static int acquire(struct lock *lkp, int extflags, int wanted);
75 static int apause(struct lock *lkp, int flags);
76 static int acquiredrain(struct lock *lkp, int extflags) ;
78 static LOCK_INLINE void
79 sharelock(struct lock *lkp, int incr) {
80 lkp->lk_flags |= LK_SHARE_NONZERO;
81 lkp->lk_sharecount += incr;
84 static LOCK_INLINE void
85 shareunlock(struct lock *lkp, int decr) {
87 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
89 if (lkp->lk_sharecount == decr) {
90 lkp->lk_flags &= ~LK_SHARE_NONZERO;
91 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
94 lkp->lk_sharecount = 0;
96 lkp->lk_sharecount -= decr;
101 * This is the waitloop optimization, and note for this to work
102 * simple_lock and simple_unlock should be subroutines to avoid
103 * optimization troubles.
106 apause(struct lock *lkp, int flags)
112 if ((lkp->lk_flags & flags) == 0)
115 for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) {
116 simple_unlock(&lkp->lk_interlock);
117 for (i = LOCK_SAMPLE_WAIT; i > 0; i--)
118 if ((lkp->lk_flags & flags) == 0)
120 simple_lock(&lkp->lk_interlock);
121 if ((lkp->lk_flags & flags) == 0)
129 acquire(struct lock *lkp, int extflags, int wanted) {
132 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
136 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
137 error = apause(lkp, wanted);
143 while ((lkp->lk_flags & wanted) != 0) {
144 lkp->lk_flags |= LK_WAIT_NONZERO;
146 simple_unlock(&lkp->lk_interlock);
147 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg,
148 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
149 simple_lock(&lkp->lk_interlock);
150 if (lkp->lk_waitcount == 1) {
151 lkp->lk_flags &= ~LK_WAIT_NONZERO;
152 lkp->lk_waitcount = 0;
160 if (extflags & LK_SLEEPFAIL) {
170 * Set, change, or release a lock.
172 * Shared requests increment the shared count. Exclusive requests set the
173 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
174 * accepted shared locks and shared-to-exclusive upgrades to go away.
178 lockmgr(lkp, flags, interlkp, p)
180 debuglockmgr(lkp, flags, interlkp, p, name, file, line)
184 struct simplelock *interlkp;
187 const char *name; /* Name of lock function */
188 const char *file; /* Name of file call is from */
189 int line; /* Line number in file */
202 simple_lock(&lkp->lk_interlock);
203 if (flags & LK_INTERLOCK)
204 simple_unlock(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 != pid) {
221 if (p && (p->p_flag & P_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 != pid || 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_NOPROC;
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 == pid) || (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 = pid;
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 == pid && pid != LK_KERNPROC) {
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 = pid;
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 != pid &&
382 lkp->lk_lockholder != LK_KERNPROC) {
383 panic("lockmgr: pid %d, not %s %d unlocking",
384 pid, "exclusive lock holder",
387 if (lkp->lk_lockholder != LK_KERNPROC) {
390 if (lkp->lk_exclusivecount == 1) {
391 lkp->lk_flags &= ~LK_HAVE_EXCL;
392 lkp->lk_lockholder = LK_NOPROC;
393 lkp->lk_exclusivecount = 0;
395 lkp->lk_exclusivecount--;
397 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
401 if (lkp->lk_flags & LK_WAIT_NONZERO)
407 * Check that we do not already hold the lock, as it can
408 * never drain if we do. Unfortunately, we have no way to
409 * check for holding a shared lock, but at least we can
410 * check for an exclusive one.
412 if (lkp->lk_lockholder == pid)
413 panic("lockmgr: draining against myself");
415 error = acquiredrain(lkp, extflags);
418 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
419 lkp->lk_lockholder = pid;
420 lkp->lk_exclusivecount = 1;
421 #if defined(DEBUG_LOCKS)
422 lkp->lk_filename = file;
423 lkp->lk_lineno = line;
424 lkp->lk_lockername = name;
430 simple_unlock(&lkp->lk_interlock);
431 panic("lockmgr: unknown locktype request %d",
432 flags & LK_TYPE_MASK);
435 if ((lkp->lk_flags & LK_WAITDRAIN) &&
436 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
437 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
438 lkp->lk_flags &= ~LK_WAITDRAIN;
439 wakeup((void *)&lkp->lk_flags);
441 simple_unlock(&lkp->lk_interlock);
446 acquiredrain(struct lock *lkp, int extflags) {
449 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
453 error = apause(lkp, LK_ALL);
457 while (lkp->lk_flags & LK_ALL) {
458 lkp->lk_flags |= LK_WAITDRAIN;
459 simple_unlock(&lkp->lk_interlock);
460 error = tsleep(&lkp->lk_flags, lkp->lk_prio,
462 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
463 simple_lock(&lkp->lk_interlock);
466 if (extflags & LK_SLEEPFAIL) {
474 * Initialize a lock; required before use.
477 lockinit(lkp, prio, wmesg, timo, flags)
485 simple_lock_init(&lkp->lk_interlock);
486 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
487 lkp->lk_sharecount = 0;
488 lkp->lk_waitcount = 0;
489 lkp->lk_exclusivecount = 0;
491 lkp->lk_wmesg = wmesg;
493 lkp->lk_lockholder = LK_NOPROC;
497 * Determine the status of a lock.
506 simple_lock(&lkp->lk_interlock);
507 if (lkp->lk_exclusivecount != 0) {
508 if (p == NULL || lkp->lk_lockholder == p->p_pid)
509 lock_type = LK_EXCLUSIVE;
511 lock_type = LK_EXCLOTHER;
512 } else if (lkp->lk_sharecount != 0)
513 lock_type = LK_SHARED;
514 simple_unlock(&lkp->lk_interlock);
519 * Determine the number of holders of a lock.
527 simple_lock(&lkp->lk_interlock);
528 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
529 simple_unlock(&lkp->lk_interlock);
534 * Print out information about state of a lock. Used by VOP_PRINT
535 * routines to display status about contained locks.
538 lockmgr_printinfo(lkp)
542 if (lkp->lk_sharecount)
543 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
545 else if (lkp->lk_flags & LK_HAVE_EXCL)
546 printf(" lock type %s: EXCL (count %d) by pid %d",
547 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder);
548 if (lkp->lk_waitcount > 0)
549 printf(" with %d pending", lkp->lk_waitcount);
552 #if defined(SIMPLELOCK_DEBUG) && (MAXCPU == 1 || defined(COMPILING_LINT))
553 #include <sys/kernel.h>
554 #include <sys/sysctl.h>
556 static int lockpausetime = 0;
557 SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, "");
559 static int simplelockrecurse;
562 * Simple lock functions so that the debugger can see from whence
563 * they are being called.
566 simple_lock_init(alp)
567 struct simplelock *alp;
574 _simple_lock(alp, id, l)
575 struct simplelock *alp;
580 if (simplelockrecurse)
582 if (alp->lock_data == 1) {
583 if (lockpausetime == -1)
584 panic("%s:%d: simple_lock: lock held", id, l);
585 printf("%s:%d: simple_lock: lock held\n", id, l);
586 if (lockpausetime == 1) {
587 Debugger("simple_lock");
588 /*BACKTRACE(curproc); */
589 } else if (lockpausetime > 1) {
590 printf("%s:%d: simple_lock: lock held...", id, l);
591 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock",
593 printf(" continuing\n");
598 curproc->p_simple_locks++;
602 _simple_lock_try(alp, id, l)
603 struct simplelock *alp;
610 if (simplelockrecurse)
614 curproc->p_simple_locks++;
619 _simple_unlock(alp, id, l)
620 struct simplelock *alp;
625 if (simplelockrecurse)
627 if (alp->lock_data == 0) {
628 if (lockpausetime == -1)
629 panic("%s:%d: simple_unlock: lock not held", id, l);
630 printf("%s:%d: simple_unlock: lock not held\n", id, l);
631 if (lockpausetime == 1) {
632 Debugger("simple_unlock");
633 /* BACKTRACE(curproc); */
634 } else if (lockpausetime > 1) {
635 printf("%s:%d: simple_unlock: lock not held...", id, l);
636 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock",
638 printf(" continuing\n");
643 curproc->p_simple_locks--;
645 #elif defined(SIMPLELOCK_DEBUG)
646 #error "SIMPLELOCK_DEBUG is not compatible with SMP!"
647 #endif /* SIMPLELOCK_DEBUG && MAXCPU == 1 */