path: root/sys/dev/raidframe/rf_stripelocks.c

/*	$OpenBSD: rf_stripelocks.c,v 1.6 2007/11/26 09:28:33 martynas Exp $	*/
/*	$NetBSD: rf_stripelocks.c,v 1.5 2000/01/08 23:45:05 oster Exp $	*/

/*
 * Copyright (c) 1995 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Authors: Mark Holland, Jim Zelenka
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */

/*
 * stripelocks.c -- Code to lock stripes for read and write access.
 *
 * The code distinguishes between read locks and write locks. There can be
 * as many readers to given stripe as desired. When a write request comes
 * in, no further readers are allowed to enter, and all subsequent requests
 * are queued in FIFO order. When the number of readers goes to zero, the
 * writer is given the lock. When a writer releases the lock, the list of
 * queued requests is scanned, and all readers up to the next writer are
 * given the lock.
 *
 * The lock table size must be one less than a power of two, but HASH_STRIPEID
 * is the only function that requires this.
 *
 * The code now supports "range locks". When you ask to lock a stripe, you
 * specify a range of addresses in that stripe that you want to lock. When
 * you acquire the lock, you've locked only this range of addresses, and
 * other threads can concurrently read/write any non-overlapping portions
 * of the stripe. The "addresses" that you lock are abstract in that you
 * can pass in anything you like. The expectation is that you'll pass in
 * the range of physical disk offsets of the parity bits you're planning
 * to update. The idea behind this, of course, is to allow sub-stripe
 * locking. The implementation is perhaps not the best imaginable; in the
 * worst case a lock release is O(n^2) in the total number of outstanding
 * requests to a given stripe. Note that if you're striping with a
 * stripe unit size equal to an entire disk (i.e. not striping), there will
 * be only one stripe and you may spend some significant number of cycles
 * searching through stripe lock descriptors.
 */

#include "rf_types.h"
#include "rf_raid.h"
#include "rf_stripelocks.h"
#include "rf_alloclist.h"
#include "rf_general.h"
#include "rf_freelist.h"
#include "rf_debugprint.h"
#include "rf_driver.h"
#include "rf_shutdown.h"

#define	Dprintf1(s,a)							\
	rf_debug_printf(s, (void *)((unsigned long)a),			\
	    NULL, NULL, NULL, NULL, NULL, NULL, NULL)
#define	Dprintf2(s,a,b)							\
	rf_debug_printf(s, (void *)((unsigned long)a),			\
	    (void *)((unsigned long)b), NULL, NULL, NULL, NULL, NULL, NULL)
#define	Dprintf3(s,a,b,c)						\
	rf_debug_printf(s, (void *)((unsigned long)a),			\
	    (void *)((unsigned long)b), (void *)((unsigned long)c),	\
	    NULL, NULL, NULL, NULL, NULL)
#define	Dprintf4(s,a,b,c,d)						\
	rf_debug_printf(s, (void *)((unsigned long)a),			\
	    (void *)((unsigned long)b), (void *)((unsigned long)c),	\
	    (void *)((unsigned long)d), NULL, NULL, NULL, NULL)
#define	Dprintf5(s,a,b,c,d,e)						\
	rf_debug_printf(s, (void *)((unsigned long)a),			\
	    (void *)((unsigned long)b), (void *)((unsigned long)c),	\
	    (void *)((unsigned long)d), (void *)((unsigned long)e),	\
	    NULL, NULL, NULL)
#define	Dprintf6(s,a,b,c,d,e,f)						\
	rf_debug_printf(s, (void *)((unsigned long)a),			\
	    (void *)((unsigned long)b), (void *)((unsigned long)c),	\
	    (void *)((unsigned long)d), (void *)((unsigned long)e),	\
	    (void *)((unsigned long)f), NULL, NULL)
#define	Dprintf7(s,a,b,c,d,e,f,g)					\
	rf_debug_printf(s, (void *)((unsigned long)a),			\
	    (void *)((unsigned long)b), (void *)((unsigned long)c),	\
	    (void *)((unsigned long)d), (void *)((unsigned long)e),	\
	    (void *)((unsigned long)f), (void *)((unsigned long)g), NULL)
#define	Dprintf8(s,a,b,c,d,e,f,g,h)					\
	rf_debug_printf(s, (void *)((unsigned long)a),			\
	    (void *)((unsigned long)b), (void *)((unsigned long)c),	\
	    (void *)((unsigned long)d), (void *)((unsigned long)e),	\
	    (void *)((unsigned long)f), (void *)((unsigned long)g),	\
	    (void *)((unsigned long)h))

#define	FLUSH

#define	HASH_STRIPEID(_sid_)	((_sid_) & (rf_lockTableSize-1))

void rf_AddToWaitersQueue(RF_LockTableEntry_t *, RF_StripeLockDesc_t *,
	RF_LockReqDesc_t *);
RF_StripeLockDesc_t *rf_AllocStripeLockDesc(RF_StripeNum_t);
void rf_FreeStripeLockDesc(RF_StripeLockDesc_t *);
void rf_PrintLockedStripes(RF_LockTableEntry_t *);

/*
 * Determines if two ranges overlap. Always yields false if either start
 * value is negative.
 */
#define	SINGLE_RANGE_OVERLAP(_strt1,_stop1,_strt2,_stop2)		\
	((_strt1 >= 0) && (_strt2 >= 0) &&				\
	 (RF_MAX(_strt1, _strt2) <= RF_MIN(_stop1, _stop2)))

/*
 * Determines if any of the ranges specified in the two lock descriptors
 * overlap each other.
 */
#define	RANGE_OVERLAP(_cand,_pred)					\
	(SINGLE_RANGE_OVERLAP((_cand)->start,  (_cand)->stop,		\
			      (_pred)->start,  (_pred)->stop) ||	\
	 SINGLE_RANGE_OVERLAP((_cand)->start2, (_cand)->stop2,		\
			      (_pred)->start,  (_pred)->stop) ||	\
	 SINGLE_RANGE_OVERLAP((_cand)->start,  (_cand)->stop,		\
			      (_pred)->start2, (_pred)->stop2) ||	\
	 SINGLE_RANGE_OVERLAP((_cand)->start2, (_cand)->stop2,		\
			      (_pred)->start2, (_pred)->stop2))

/*
 * Determines if a candidate lock request conflicts with a predecessor
 * lock req. Note that the arguments are not interchangeable.
 * The rules are:
 *  A candidate read conflicts with a predecessor write if any ranges overlap.
 *  A candidate write conflicts with a predecessor read if any ranges overlap.
 *  A candidate write conflicts with a predecessor write if any ranges overlap.
 */
#define	STRIPELOCK_CONFLICT(_cand,_pred)				\
	(RANGE_OVERLAP((_cand), (_pred)) &&				\
	 (((((_cand)->type == RF_IO_TYPE_READ) &&			\
	    ((_pred)->type == RF_IO_TYPE_WRITE)) ||			\
	   (((_cand)->type == RF_IO_TYPE_WRITE) &&			\
	    ((_pred)->type == RF_IO_TYPE_READ)) ||			\
	   (((_cand)->type == RF_IO_TYPE_WRITE) &&			\
	    ((_pred)->type == RF_IO_TYPE_WRITE)))))

static RF_FreeList_t *rf_stripelock_freelist;
#define	RF_MAX_FREE_STRIPELOCK		128
#define	RF_STRIPELOCK_INC		  8
#define	RF_STRIPELOCK_INITIAL		 32

void rf_ShutdownStripeLockFreeList(void *);
void rf_RaidShutdownStripeLocks(void *);

void
rf_ShutdownStripeLockFreeList(void *ignored)
{
	RF_FREELIST_DESTROY(rf_stripelock_freelist, next,
	    (RF_StripeLockDesc_t *));
}

int
rf_ConfigureStripeLockFreeList(RF_ShutdownList_t **listp)
{
	unsigned mask;
	int rc;

	RF_FREELIST_CREATE(rf_stripelock_freelist, RF_MAX_FREE_STRIPELOCK,
	    RF_STRIPELOCK_INITIAL, sizeof(RF_StripeLockDesc_t));
	rc = rf_ShutdownCreate(listp, rf_ShutdownStripeLockFreeList, NULL);
	if (rc) {
		RF_ERRORMSG3("Unable to add to shutdown list file %s"
		    " line %d rc=%d.\n", __FILE__, __LINE__, rc);
		rf_ShutdownStripeLockFreeList(NULL);
		return (rc);
	}
	RF_FREELIST_PRIME(rf_stripelock_freelist, RF_STRIPELOCK_INITIAL, next,
	    (RF_StripeLockDesc_t *));
	for (mask = 0x1; mask; mask <<= 1)
		if (rf_lockTableSize == mask)
			break;
	if (!mask) {
		printf("[WARNING:  lock table size must be a power of two."
		    " Setting to %d.]\n", RF_DEFAULT_LOCK_TABLE_SIZE);
		rf_lockTableSize = RF_DEFAULT_LOCK_TABLE_SIZE;
	}
	return (0);
}

RF_LockTableEntry_t *
rf_MakeLockTable(void)
{
	RF_LockTableEntry_t *lockTable;
	int i, rc;

	RF_Calloc(lockTable, ((int) rf_lockTableSize),
	    sizeof(RF_LockTableEntry_t), (RF_LockTableEntry_t *));
	if (lockTable == NULL)
		return (NULL);
	for (i = 0; i < rf_lockTableSize; i++) {
		rc = rf_mutex_init(&lockTable[i].mutex);
		if (rc) {
			RF_ERRORMSG3("Unable to init mutex file %s line %d"
			    " rc=%d.\n", __FILE__, __LINE__, rc);
			/* XXX Clean up other mutexes. */
			return (NULL);
		}
	}
	return (lockTable);
}

void
rf_ShutdownStripeLocks(RF_LockTableEntry_t *lockTable)
{
	int i;

	if (rf_stripeLockDebug) {
		rf_PrintLockedStripes(lockTable);
	}
	for (i = 0; i < rf_lockTableSize; i++) {
		rf_mutex_destroy(&lockTable[i].mutex);
	}
	RF_Free(lockTable, rf_lockTableSize * sizeof(RF_LockTableEntry_t));
}

void
rf_RaidShutdownStripeLocks(void *arg)
{
	RF_Raid_t *raidPtr = (RF_Raid_t *) arg;
	rf_ShutdownStripeLocks(raidPtr->lockTable);
}

int
rf_ConfigureStripeLocks(RF_ShutdownList_t **listp, RF_Raid_t *raidPtr,
    RF_Config_t *cfgPtr)
{
	int rc;

	raidPtr->lockTable = rf_MakeLockTable();
	if (raidPtr->lockTable == NULL)
		return (ENOMEM);
	rc = rf_ShutdownCreate(listp, rf_RaidShutdownStripeLocks, raidPtr);
	if (rc) {
		RF_ERRORMSG3("Unable to add to shutdown list file %s line %d"
		    " rc=%d.\n", __FILE__, __LINE__, rc);
		rf_ShutdownStripeLocks(raidPtr->lockTable);
		return (rc);
	}
	return (0);
}

/*
 * Returns 0 if you've got the lock, and non-zero if you have to wait.
 * If and only if you have to wait, we'll cause cbFunc to get invoked
 * with cbArg when you are granted the lock. We store a tag in *releaseTag
 * that you need to give back to us when you release the lock.
 */
int
rf_AcquireStripeLock(RF_LockTableEntry_t *lockTable, RF_StripeNum_t stripeID,
    RF_LockReqDesc_t *lockReqDesc)
{
	RF_StripeLockDesc_t *lockDesc;
	RF_LockReqDesc_t *p;
	int tid = 0, hashval = HASH_STRIPEID(stripeID);
	int retcode = 0;

	RF_ASSERT(RF_IO_IS_R_OR_W(lockReqDesc->type));

	if (rf_stripeLockDebug) {
		if (stripeID == -1)
			Dprintf1("[%d] Lock acquisition suppressed"
			    " (stripeID == -1).\n", tid);
		else {
			Dprintf8("[%d] Trying to acquire stripe lock table"
			    " 0x%lx SID %ld type %c range %ld-%ld, range2"
			    " %ld-%ld hashval %d.\n", tid,
			    (unsigned long) lockTable, stripeID,
			    lockReqDesc->type, lockReqDesc->start,
			    lockReqDesc->stop, lockReqDesc->start2,
			    lockReqDesc->stop2);
			Dprintf3("[%d] lock %ld hashval %d.\n", tid, stripeID,
			    hashval);
			FLUSH;
		}
	}
	if (stripeID == -1)
		return (0);
	lockReqDesc->next = NULL;	/* Just to be sure. */

	RF_LOCK_MUTEX(lockTable[hashval].mutex);
	for (lockDesc = lockTable[hashval].descList; lockDesc;
	     lockDesc = lockDesc->next) {
		if (lockDesc->stripeID == stripeID)
			break;
	}

	if (!lockDesc) {
		/* No entry in table => no one reading or writing. */
		lockDesc = rf_AllocStripeLockDesc(stripeID);
		lockDesc->next = lockTable[hashval].descList;
		lockTable[hashval].descList = lockDesc;
		if (lockReqDesc->type == RF_IO_TYPE_WRITE)
			lockDesc->nWriters++;
		lockDesc->granted = lockReqDesc;
		if (rf_stripeLockDebug) {
			Dprintf7("[%d] no one waiting: lock %ld %c %ld-%ld"
			    " %ld-%ld granted.\n", tid, stripeID,
			    lockReqDesc->type,
			    lockReqDesc->start, lockReqDesc->stop,
			    lockReqDesc->start2, lockReqDesc->stop2);
			FLUSH;
		}
	} else {

		if (lockReqDesc->type == RF_IO_TYPE_WRITE)
			lockDesc->nWriters++;

		if (lockDesc->nWriters == 0) {
			/*
			 * No need to search any lists if there are no writers
			 * anywhere.
			 */
			lockReqDesc->next = lockDesc->granted;
			lockDesc->granted = lockReqDesc;
			if (rf_stripeLockDebug) {
				Dprintf7("[%d] no writers: lock %ld %c %ld-%ld"
				    " %ld-%ld granted.\n", tid,
				    stripeID, lockReqDesc->type,
				    lockReqDesc->start, lockReqDesc->stop,
				    lockReqDesc->start2, lockReqDesc->stop2);
				FLUSH;
			}
		} else {
			/*
			 * Search the granted & waiting lists for a conflict.
			 * Stop searching as soon as we find one.
			 */
			retcode = 0;
			for (p = lockDesc->granted; p; p = p->next)
				if (STRIPELOCK_CONFLICT(lockReqDesc, p)) {
					retcode = 1;
					break;
				}
			if (!retcode)
				for (p = lockDesc->waitersH; p; p = p->next)
					if (STRIPELOCK_CONFLICT(lockReqDesc, p))
					{
						retcode = 2;
						break;
					}
			if (!retcode) {
				/* No conflicts found => grant lock */
				lockReqDesc->next = lockDesc->granted;
				lockDesc->granted = lockReqDesc;
				if (rf_stripeLockDebug) {
					Dprintf7("[%d] no conflicts: lock %ld"
					    " %c %ld-%ld %ld-%ld granted.\n",
					    tid, stripeID, lockReqDesc->type,
					    lockReqDesc->start,
					    lockReqDesc->stop,
					    lockReqDesc->start2,
					    lockReqDesc->stop2);
					FLUSH;
				}
			} else {
				if (rf_stripeLockDebug) {
					Dprintf6("[%d] conflict: lock %ld %c"
					    " %ld-%ld hashval=%d not"
					    " granted.\n", tid, stripeID,
					    lockReqDesc->type,
					    lockReqDesc->start,
					    lockReqDesc->stop,
					    hashval);
					Dprintf3("[%d] lock %ld retcode=%d.\n",
					    tid, stripeID, retcode);
					FLUSH;
				}
				/* Conflict => the current access must wait. */
				rf_AddToWaitersQueue(lockTable, lockDesc,
				    lockReqDesc);
			}
		}
	}

	RF_UNLOCK_MUTEX(lockTable[hashval].mutex);
	return (retcode);
}

void
rf_ReleaseStripeLock(RF_LockTableEntry_t *lockTable, RF_StripeNum_t stripeID,
    RF_LockReqDesc_t *lockReqDesc)
{
	RF_StripeLockDesc_t *lockDesc, *ld_t;
	RF_LockReqDesc_t *lr, *lr_t, *callbacklist, *t;
	RF_IoType_t type = lockReqDesc->type;
	int tid = 0, hashval = HASH_STRIPEID(stripeID);
	int release_it, consider_it;
	RF_LockReqDesc_t *candidate, *candidate_t, *predecessor;

	RF_ASSERT(RF_IO_IS_R_OR_W(type));

	if (rf_stripeLockDebug) {
		if (stripeID == -1)
			Dprintf1("[%d] Lock release suppressed"
			    " (stripeID == -1).\n", tid);
		else {
			Dprintf8("[%d] Releasing stripe lock on stripe ID %ld,"
			    " type %c range %ld-%ld %ld-%ld table 0x%lx.\n",
			    tid, stripeID, lockReqDesc->type,
			    lockReqDesc->start, lockReqDesc->stop,
			    lockReqDesc->start2, lockReqDesc->stop2,
			    lockTable);
			FLUSH;
		}
	}
	if (stripeID == -1)
		return;

	RF_LOCK_MUTEX(lockTable[hashval].mutex);

	/* Find the stripe lock descriptor. */
	for (ld_t = NULL, lockDesc = lockTable[hashval].descList;
	     lockDesc; ld_t = lockDesc, lockDesc = lockDesc->next) {
		if (lockDesc->stripeID == stripeID)
			break;
	}
	RF_ASSERT(lockDesc);	/*
				 * Major error to release a lock that doesn't
				 * exist.
				 */

	/* Find the stripe lock request descriptor & delete it from the list. */
	for (lr_t = NULL, lr = lockDesc->granted; lr; lr_t = lr, lr = lr->next)
		if (lr == lockReqDesc)
			break;

	RF_ASSERT(lr && (lr == lockReqDesc));	/*
						 * Major error to release a
						 * lock that hasn't been
						 * granted.
						 */
	if (lr_t)
		lr_t->next = lr->next;
	else {
		RF_ASSERT(lr == lockDesc->granted);
		lockDesc->granted = lr->next;
	}
	lr->next = NULL;

	if (lockReqDesc->type == RF_IO_TYPE_WRITE)
		lockDesc->nWriters--;

	/*
	 * Search through the waiters list to see if anyone needs to be woken
	 * up. For each such descriptor in the wait list, we check it against
	 * everything granted and against everything _in front_ of it in the
	 * waiters queue. If it conflicts with none of these, we release it.
	 *
	 * DON'T TOUCH THE TEMPLINK POINTER OF ANYTHING IN THE GRANTED LIST
	 * HERE.
	 * This will roach the case where the callback tries to acquire a new
	 * lock in the same stripe. There are some asserts to try and detect
	 * this.
	 *
	 * We apply 2 performance optimizations:
	 * (1) If releasing this lock results in no more writers to this
	 *     stripe, we just release everybody waiting, since we place no
	 *     restrictions on the number of concurrent reads.
	 * (2) We consider as candidates for wakeup only those waiters that
	 *     have a range overlap with either the descriptor being woken up
	 *     or with something in the callbacklist (i.e. something we've
	 *     just now woken up).
	 * This allows us to avoid the long evaluation for some descriptors.
	 */

	callbacklist = NULL;
	if (lockDesc->nWriters == 0) {	/* Performance tweak (1). */
		while (lockDesc->waitersH) {

			lr = lockDesc->waitersH;	/*
							 * Delete from waiters
							 * list.
							 */
			lockDesc->waitersH = lr->next;

			RF_ASSERT(lr->type == RF_IO_TYPE_READ);

			lr->next = lockDesc->granted;	/*
							 * Add to granted list.
							 */
			lockDesc->granted = lr;

			RF_ASSERT(!lr->templink);
			lr->templink = callbacklist;	/*
							 * Put on callback list
							 * so that we'll invoke
							 * callback below.
							 */
			callbacklist = lr;
			if (rf_stripeLockDebug) {
				Dprintf8("[%d] No writers: granting lock"
				    " stripe ID %ld, type %c range %ld-%l"
				    "d %ld-%ld table 0x%lx.\n", tid, stripeID,
				    lr->type, lr->start, lr->stop,
				    lr->start2, lr->stop2,
				    (unsigned long) lockTable);
				FLUSH;
			}
		}
		lockDesc->waitersT = NULL;	/*
						 * We've purged the whole
						 * waiters list.
						 */

	} else
		for (candidate_t = NULL, candidate = lockDesc->waitersH;
		     candidate;) {

			/* Performance tweak (2). */
			consider_it = 0;
			if (RANGE_OVERLAP(lockReqDesc, candidate))
				consider_it = 1;
			else
				for (t = callbacklist; t; t = t->templink)
					if (RANGE_OVERLAP(t, candidate)) {
						consider_it = 1;
						break;
					}
			if (!consider_it) {
				if (rf_stripeLockDebug) {
					Dprintf8("[%d] No overlap: rejecting"
					    " candidate stripeID %ld, type %c"
					    " range %ld-%ld %ld-%ld table"
					    " 0x%lx.\n", tid, stripeID,
					    candidate->type,
					    candidate->start, candidate->stop,
					    candidate->start2, candidate->stop2,
					    (unsigned long) lockTable);
					FLUSH;
				}
				candidate_t = candidate;
				candidate = candidate->next;
				continue;
			}
			/*
			 * We have a candidate for release. Check to make
			 * sure it is not blocked by any granted locks.
			 */
			release_it = 1;
			for (predecessor = lockDesc->granted; predecessor;
			     predecessor = predecessor->next) {
				if (STRIPELOCK_CONFLICT(candidate, predecessor))
				{
					if (rf_stripeLockDebug) {
						Dprintf8("[%d] Conflicts with"
						    " granted lock: rejecting"
						    " candidate stripeID %ld,"
						    " type %c range %ld-%ld"
						    " %ld-%ld table 0x%lx.\n",
						    tid, stripeID,
						    candidate->type,
						    candidate->start,
						    candidate->stop,
						    candidate->start2,
						    candidate->stop2,
						    (unsigned long) lockTable);
						FLUSH;
					}
					release_it = 0;
					break;
				}
			}

			/*
			 * Now check to see if the candidate is blocked by any
			 * waiters that occur before it in the wait queue.
			 */
			if (release_it)
				for (predecessor = lockDesc->waitersH;
				     predecessor != candidate;
				     predecessor = predecessor->next) {
					if (STRIPELOCK_CONFLICT(candidate,
					    predecessor)) {
						if (rf_stripeLockDebug) {
							Dprintf8("[%d]"
							    " Conflicts with"
							    " waiting lock:"
							    " rejecting"
							    " candidate"
							    " stripeID %ld,"
							    " type %c"
							    " range %ld-%ld"
							    " %ld-%ld"
							    " table 0x%lx.\n",
							    tid, stripeID,
							    candidate->type,
							    candidate->start,
							    candidate->stop,
							    candidate->start2,
							    candidate->stop2,
							    (unsigned long)
							     lockTable);
							FLUSH;
						}
						release_it = 0;
						break;
					}
				}

			/* Release it if indicated. */
			if (release_it) {
				if (rf_stripeLockDebug) {
					Dprintf8("[%d] Granting lock to"
					    " candidate stripeID %ld, type %c"
					    " range %ld-%ld %ld-%ld table"
					    " 0x%lx.\n", tid, stripeID,
					    candidate->type,
					    candidate->start, candidate->stop,
					    candidate->start2, candidate->stop2,
					    (unsigned long) lockTable);
					FLUSH;
				}
				if (candidate_t) {
					candidate_t->next = candidate->next;
					if (lockDesc->waitersT == candidate)
						/*
						 * Cannot be waitersH
						 * since candidate_t is
						 * not NULL.
						 */
						lockDesc->waitersT =
						    candidate_t;
				} else {
					RF_ASSERT(candidate ==
					    lockDesc->waitersH);
					lockDesc->waitersH =
					    lockDesc->waitersH->next;
					if (!lockDesc->waitersH)
						lockDesc->waitersT = NULL;
				}
				/* Move it to the granted list. */
				candidate->next = lockDesc->granted;
				lockDesc->granted = candidate;

				RF_ASSERT(!candidate->templink);
				/*
				 * Put it on the list of things to be called
				 * after we release the mutex.
				 */
				candidate->templink = callbacklist;
				callbacklist = candidate;

				if (!candidate_t)
					candidate = lockDesc->waitersH;
				else
					/*
					 * Continue with the rest of the list.
					 */
					candidate = candidate_t->next;
			} else {
				candidate_t = candidate;
				/* Continue with the rest of the list. */
				candidate = candidate->next;
			}
		}

	/* Delete the descriptor if no one is waiting or active. */
	if (!lockDesc->granted && !lockDesc->waitersH) {
		RF_ASSERT(lockDesc->nWriters == 0);
		if (rf_stripeLockDebug) {
			Dprintf3("[%d] Last lock released (table 0x%lx):"
			    " deleting desc for stripeID %ld.\n", tid,
			    (unsigned long) lockTable, stripeID);
			FLUSH;
		}
		if (ld_t)
			ld_t->next = lockDesc->next;
		else {
			RF_ASSERT(lockDesc == lockTable[hashval].descList);
			lockTable[hashval].descList = lockDesc->next;
		}
		rf_FreeStripeLockDesc(lockDesc);
		lockDesc = NULL;	/* Only for the ASSERT below. */
	}
	RF_UNLOCK_MUTEX(lockTable[hashval].mutex);

	/*
	 * Now that we've unlocked the mutex, invoke the callback on all the
	 * descriptors in the list.
	 */
	RF_ASSERT(!((callbacklist) && (!lockDesc)));	/*
							 * If we deleted the
							 * descriptor, we should
							 * have no callbacks to
							 * do.
							 */
	for (candidate = callbacklist; candidate;) {
		t = candidate;
		candidate = candidate->templink;
		t->templink = NULL;
		(t->cbFunc) (t->cbArg);
	}
}

/* Must have the indicated lock table mutex upon entry. */
void
rf_AddToWaitersQueue(RF_LockTableEntry_t *lockTable,
    RF_StripeLockDesc_t *lockDesc, RF_LockReqDesc_t *lockReqDesc)
{
	int tid;

	if (rf_stripeLockDebug) {
		Dprintf3("[%d] Waiting on lock for stripe %ld table 0x%lx.\n",
		    tid, lockDesc->stripeID, (unsigned long) lockTable);
		FLUSH;
	}
	if (!lockDesc->waitersH) {
		lockDesc->waitersH = lockDesc->waitersT = lockReqDesc;
	} else {
		lockDesc->waitersT->next = lockReqDesc;
		lockDesc->waitersT = lockReqDesc;
	}
}

RF_StripeLockDesc_t *
rf_AllocStripeLockDesc(RF_StripeNum_t stripeID)
{
	RF_StripeLockDesc_t *p;

	RF_FREELIST_GET(rf_stripelock_freelist, p, next,
	    (RF_StripeLockDesc_t *));
	if (p) {
		p->stripeID = stripeID;
	}
	return (p);
}

void
rf_FreeStripeLockDesc(RF_StripeLockDesc_t *p)
{
	RF_FREELIST_FREE(rf_stripelock_freelist, p, next);
}

void
rf_PrintLockedStripes(RF_LockTableEntry_t *lockTable)
{
	int i, j, foundone = 0, did;
	RF_StripeLockDesc_t *p;
	RF_LockReqDesc_t *q;

	RF_LOCK_MUTEX(rf_printf_mutex);
	printf("Locked stripes:\n");
	for (i = 0; i < rf_lockTableSize; i++)
		if (lockTable[i].descList) {
			foundone = 1;
			for (p = lockTable[i].descList; p; p = p->next) {
				printf("Stripe ID 0x%lx (%d) nWriters %d\n",
				    (long) p->stripeID, (int) p->stripeID,
				    p->nWriters);

				if (!(p->granted))
					printf("Granted: (none)\n");
				else
					printf("Granted:\n");
				for (did = 1, j = 0, q = p->granted; q;
				     j++, q = q->next) {
					printf("  %c(%ld-%ld", q->type,
					    (long) q->start, (long) q->stop);
					if (q->start2 != -1)
						printf(",%ld-%ld) ",
						    (long) q->start2,
						    (long) q->stop2);
					else
						printf(") ");
					if (j && !(j % 4)) {
						printf("\n");
						did = 1;
					} else
						did = 0;
				}
				if (!did)
					printf("\n");

				if (!(p->waitersH))
					printf("Waiting: (none)\n");
				else
					printf("Waiting:\n");
				for (did = 1, j = 0, q = p->waitersH; q;
				     j++, q = q->next) {
					printf("%c(%ld-%ld", q->type,
					    (long) q->start, (long) q->stop);
					if (q->start2 != -1)
						printf(",%ld-%ld) ",
						    (long) q->start2,
						    (long) q->stop2);
					else
						printf(") ");
					if (j && !(j % 4)) {
						printf("\n         ");
						did = 1;
					} else
						did = 0;
				}
				if (!did)
					printf("\n");
			}
		}
	if (!foundone)
		printf("(none)\n");
	else
		printf("\n");
	RF_UNLOCK_MUTEX(rf_printf_mutex);
}