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.
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13 * modification, are permitted provided that the following conditions
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22 * This product includes software developed by the University of
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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 1.5 2003/07/21 07:57:47 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 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 acquire(struct lock *lkp, int extflags, int wanted)
105 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
109 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
110 if ((lkp->lk_flags & wanted) == 0)
115 while ((lkp->lk_flags & wanted) != 0) {
116 lkp->lk_flags |= LK_WAIT_NONZERO;
118 lwkt_reltoken(&lkp->lk_interlock);
119 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg,
120 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
121 lwkt_gettoken(&lkp->lk_interlock);
122 if (lkp->lk_waitcount == 1) {
123 lkp->lk_flags &= ~LK_WAIT_NONZERO;
124 lkp->lk_waitcount = 0;
132 if (extflags & LK_SLEEPFAIL) {
142 * Set, change, or release a lock.
144 * Shared requests increment the shared count. Exclusive requests set the
145 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
146 * accepted shared locks and shared-to-exclusive upgrades to go away.
150 lockmgr(struct lock *lkp, u_int flags, struct lwkt_token *interlkp,
153 debuglockmgr(struct lock *lkp, u_int flags, struct lwkt_token *interlkp,
154 struct thread *td, const char *name, const char *file, int line)
162 lwkt_gettoken(&lkp->lk_interlock);
163 if (flags & LK_INTERLOCK)
164 lwkt_reltoken(interlkp);
166 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
168 switch (flags & LK_TYPE_MASK) {
172 * If we are not the exclusive lock holder, we have to block
173 * while there is an exclusive lock holder or while an
174 * exclusive lock request or upgrade request is in progress.
176 * However, if P_DEADLKTREAT is set, we override exclusive
177 * lock requests or upgrade requests ( but not the exclusive
180 if (lkp->lk_lockholder != td) {
181 if (td->td_flags & TDF_DEADLKTREAT) {
191 LK_HAVE_EXCL | LK_WANT_EXCL |
202 * We hold an exclusive lock, so downgrade it to shared.
203 * An alternative would be to fail with EDEADLK.
207 /* fall into downgrade */
210 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0)
211 panic("lockmgr: not holding exclusive lock");
212 sharelock(lkp, lkp->lk_exclusivecount);
213 lkp->lk_exclusivecount = 0;
214 lkp->lk_flags &= ~LK_HAVE_EXCL;
215 lkp->lk_lockholder = LK_NOTHREAD;
216 if (lkp->lk_waitcount)
222 * If another process is ahead of us to get an upgrade,
223 * then we want to fail rather than have an intervening
226 if (lkp->lk_flags & LK_WANT_UPGRADE) {
232 /* fall into normal upgrade */
236 * Upgrade a shared lock to an exclusive one. If another
237 * shared lock has already requested an upgrade to an
238 * exclusive lock, our shared lock is released and an
239 * exclusive lock is requested (which will be granted
240 * after the upgrade). If we return an error, the file
241 * will always be unlocked.
243 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0))
244 panic("lockmgr: upgrade exclusive lock");
248 * If we are just polling, check to see if we will block.
250 if ((extflags & LK_NOWAIT) &&
251 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
252 lkp->lk_sharecount > 1)) {
256 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
258 * We are first shared lock to request an upgrade, so
259 * request upgrade and wait for the shared count to
260 * drop to zero, then take exclusive lock.
262 lkp->lk_flags |= LK_WANT_UPGRADE;
263 error = acquire(lkp, extflags, LK_SHARE_NONZERO);
264 lkp->lk_flags &= ~LK_WANT_UPGRADE;
268 lkp->lk_flags |= LK_HAVE_EXCL;
269 lkp->lk_lockholder = td;
270 if (lkp->lk_exclusivecount != 0)
271 panic("lockmgr: non-zero exclusive count");
272 lkp->lk_exclusivecount = 1;
273 #if defined(DEBUG_LOCKS)
274 lkp->lk_filename = file;
275 lkp->lk_lineno = line;
276 lkp->lk_lockername = name;
282 * Someone else has requested upgrade. Release our shared
283 * lock, awaken upgrade requestor if we are the last shared
284 * lock, then request an exclusive lock.
286 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
289 /* fall into exclusive request */
292 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
296 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
297 panic("lockmgr: locking against myself");
298 if ((extflags & LK_CANRECURSE) != 0) {
299 lkp->lk_exclusivecount++;
305 * If we are just polling, check to see if we will sleep.
307 if ((extflags & LK_NOWAIT) &&
308 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
313 * Try to acquire the want_exclusive flag.
315 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
318 lkp->lk_flags |= LK_WANT_EXCL;
320 * Wait for shared locks and upgrades to finish.
322 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
323 lkp->lk_flags &= ~LK_WANT_EXCL;
326 lkp->lk_flags |= LK_HAVE_EXCL;
327 lkp->lk_lockholder = td;
328 if (lkp->lk_exclusivecount != 0)
329 panic("lockmgr: non-zero exclusive count");
330 lkp->lk_exclusivecount = 1;
331 #if defined(DEBUG_LOCKS)
332 lkp->lk_filename = file;
333 lkp->lk_lineno = line;
334 lkp->lk_lockername = name;
340 if (lkp->lk_exclusivecount != 0) {
341 if (lkp->lk_lockholder != td &&
342 lkp->lk_lockholder != LK_KERNTHREAD) {
343 panic("lockmgr: pid %d, not %s thr %p unlocking",
344 (td->td_proc ? td->td_proc->p_pid : -99),
345 "exclusive lock holder",
348 if (lkp->lk_lockholder != LK_KERNTHREAD) {
351 if (lkp->lk_exclusivecount == 1) {
352 lkp->lk_flags &= ~LK_HAVE_EXCL;
353 lkp->lk_lockholder = LK_NOTHREAD;
354 lkp->lk_exclusivecount = 0;
356 lkp->lk_exclusivecount--;
358 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
362 if (lkp->lk_flags & LK_WAIT_NONZERO)
368 * Check that we do not already hold the lock, as it can
369 * never drain if we do. Unfortunately, we have no way to
370 * check for holding a shared lock, but at least we can
371 * check for an exclusive one.
373 if (lkp->lk_lockholder == td)
374 panic("lockmgr: draining against myself");
376 error = acquiredrain(lkp, extflags);
379 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
380 lkp->lk_lockholder = td;
381 lkp->lk_exclusivecount = 1;
382 #if defined(DEBUG_LOCKS)
383 lkp->lk_filename = file;
384 lkp->lk_lineno = line;
385 lkp->lk_lockername = name;
391 lwkt_reltoken(&lkp->lk_interlock);
392 panic("lockmgr: unknown locktype request %d",
393 flags & LK_TYPE_MASK);
396 if ((lkp->lk_flags & LK_WAITDRAIN) &&
397 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
398 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
399 lkp->lk_flags &= ~LK_WAITDRAIN;
400 wakeup((void *)&lkp->lk_flags);
402 lwkt_reltoken(&lkp->lk_interlock);
407 acquiredrain(struct lock *lkp, int extflags)
411 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
415 if ((lkp->lk_flags & LK_ALL) == 0)
418 while (lkp->lk_flags & LK_ALL) {
419 lkp->lk_flags |= LK_WAITDRAIN;
420 lwkt_reltoken(&lkp->lk_interlock);
421 error = tsleep(&lkp->lk_flags, lkp->lk_prio,
423 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
424 lwkt_gettoken(&lkp->lk_interlock);
427 if (extflags & LK_SLEEPFAIL) {
435 * Initialize a lock; required before use.
438 lockinit(lkp, prio, wmesg, timo, flags)
445 lwkt_inittoken(&lkp->lk_interlock);
446 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
447 lkp->lk_sharecount = 0;
448 lkp->lk_waitcount = 0;
449 lkp->lk_exclusivecount = 0;
451 lkp->lk_wmesg = wmesg;
453 lkp->lk_lockholder = LK_NOTHREAD;
457 * Determine the status of a lock.
460 lockstatus(struct lock *lkp, struct thread *td)
464 lwkt_gettoken(&lkp->lk_interlock);
465 if (lkp->lk_exclusivecount != 0) {
466 if (td == NULL || lkp->lk_lockholder == td)
467 lock_type = LK_EXCLUSIVE;
469 lock_type = LK_EXCLOTHER;
470 } else if (lkp->lk_sharecount != 0) {
471 lock_type = LK_SHARED;
473 lwkt_reltoken(&lkp->lk_interlock);
478 * Determine the number of holders of a lock.
486 lwkt_gettoken(&lkp->lk_interlock);
487 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
488 lwkt_reltoken(&lkp->lk_interlock);
493 * Print out information about state of a lock. Used by VOP_PRINT
494 * routines to display status about contained locks.
497 lockmgr_printinfo(lkp)
500 struct thread *td = lkp->lk_lockholder;
503 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
508 if (lkp->lk_sharecount)
509 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
511 else if (lkp->lk_flags & LK_HAVE_EXCL)
512 printf(" lock type %s: EXCL (count %d) by td %p pid %d",
513 lkp->lk_wmesg, lkp->lk_exclusivecount, td,
515 if (lkp->lk_waitcount > 0)
516 printf(" with %d pending", lkp->lk_waitcount);