lock_deadlock.c

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/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2002
 *	Sleepycat Software.  All rights reserved.
 */

#include "db_config.h"

#ifndef lint
static const char revid[] = "$Id: lock_deadlock.c,v 11.54 2002/08/06 05:05:21 bostic Exp $";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <string.h>
#endif

#include "db_int.h"
#include "dbinc/db_shash.h"
#include "dbinc/lock.h"
#include "dbinc/txn.h"
#include "dbinc/rep.h"

#define	ISSET_MAP(M, N)	((M)[(N) / 32] & (1 << (N) % 32))

#define	CLEAR_MAP(M, N) {						\
	u_int32_t __i;							\
	for (__i = 0; __i < (N); __i++)					\
		(M)[__i] = 0;						\
}

#define	SET_MAP(M, B)	((M)[(B) / 32] |= (1 << ((B) % 32)))
#define	CLR_MAP(M, B)	((M)[(B) / 32] &= ~(1 << ((B) % 32)))

#define	OR_MAP(D, S, N)	{						\
	u_int32_t __i;							\
	for (__i = 0; __i < (N); __i++)					\
		D[__i] |= S[__i];					\
}
#define	BAD_KILLID	0xffffffff

typedef struct {
	int		valid;
	int		self_wait;
	u_int32_t	count;
	u_int32_t	id;
	u_int32_t	last_lock;
	u_int32_t	last_locker_id;
	db_pgno_t	pgno;
} locker_info;

static int  __dd_abort __P((DB_ENV *, locker_info *));
static int  __dd_build __P((DB_ENV *,
	    u_int32_t, u_int32_t **, u_int32_t *, u_int32_t *, locker_info **));
static int  __dd_find __P((DB_ENV *,
	    u_int32_t *, locker_info *, u_int32_t, u_int32_t, u_int32_t ***));
static int  __dd_isolder __P((u_int32_t, u_int32_t, u_int32_t, u_int32_t));
static int __dd_verify __P((locker_info *, u_int32_t *, u_int32_t *,
	    u_int32_t *, u_int32_t, u_int32_t, u_int32_t));

#ifdef DIAGNOSTIC
static void __dd_debug
	    __P((DB_ENV *, locker_info *, u_int32_t *, u_int32_t, u_int32_t));
#endif

/*
 * lock_detect --
 *
 * PUBLIC: int __lock_detect __P((DB_ENV *, u_int32_t, u_int32_t, int *));
 */
int
__lock_detect(dbenv, flags, atype, abortp)
	DB_ENV *dbenv;
	u_int32_t flags, atype;
	int *abortp;
{
	DB_LOCKREGION *region;
	DB_LOCKTAB *lt;
	DB_TXNMGR *tmgr;
	locker_info *idmap;
	u_int32_t *bitmap, *copymap, **deadp, **free_me, *tmpmap;
	u_int32_t i, keeper, killid, limit, nalloc, nlockers;
	u_int32_t lock_max, txn_max;
	int ret;

	PANIC_CHECK(dbenv);
	ENV_REQUIRES_CONFIG(dbenv,
	    dbenv->lk_handle, "DB_ENV->lock_detect", DB_INIT_LOCK);

	/* Validate arguments. */
	if ((ret = __db_fchk(dbenv, "DB_ENV->lock_detect", flags, 0)) != 0)
		return (ret);
	switch (atype) {
	case DB_LOCK_DEFAULT:
	case DB_LOCK_EXPIRE:
	case DB_LOCK_MAXLOCKS:
	case DB_LOCK_MINLOCKS:
	case DB_LOCK_MINWRITE:
	case DB_LOCK_OLDEST:
	case DB_LOCK_RANDOM:
	case DB_LOCK_YOUNGEST:
		break;
	default:
		__db_err(dbenv,
	    "DB_ENV->lock_detect: unknown deadlock detection mode specified");
		return (EINVAL);
	}

	/*
	 * If this environment is a replication client, then we must use the
	 * MINWRITE detection discipline.
	 */
	if (__rep_is_client(dbenv))
		atype = DB_LOCK_MINWRITE;

	free_me = NULL;

	lt = dbenv->lk_handle;
	if (abortp != NULL)
		*abortp = 0;

	/* Check if a detector run is necessary. */
	LOCKREGION(dbenv, lt);

	/* Make a pass only if auto-detect would run. */
	region = lt->reginfo.primary;

	if (region->need_dd == 0) {
		UNLOCKREGION(dbenv, lt);
		return (0);
	}

	/* Reset need_dd, so we know we've run the detector. */
	region->need_dd = 0;

	/* Build the waits-for bitmap. */
	ret = __dd_build(dbenv, atype, &bitmap, &nlockers, &nalloc, &idmap);
	lock_max = region->stat.st_cur_maxid;
	UNLOCKREGION(dbenv, lt);

	/*
	 * We need the cur_maxid from the txn region as well.  In order
	 * to avoid tricky synchronization between the lock and txn
	 * regions, we simply unlock the lock region and then lock the
	 * txn region.  This introduces a small window during which the
	 * transaction system could then wrap.  We're willing to return
	 * the wrong answer for "oldest" or "youngest" in those rare
	 * circumstances.
	 */
	tmgr = dbenv->tx_handle;
	if (tmgr != NULL) {
		R_LOCK(dbenv, &tmgr->reginfo);
		txn_max = ((DB_TXNREGION *)tmgr->reginfo.primary)->cur_maxid;
		R_UNLOCK(dbenv, &tmgr->reginfo);
	} else
		txn_max = TXN_MAXIMUM;
	if (ret != 0 || atype == DB_LOCK_EXPIRE)
		return (ret);

	if (nlockers == 0)
		return (0);
#ifdef DIAGNOSTIC
	if (FLD_ISSET(dbenv->verbose, DB_VERB_WAITSFOR))
		__dd_debug(dbenv, idmap, bitmap, nlockers, nalloc);
#endif
	/* Now duplicate the bitmaps so we can verify deadlock participants. */
	if ((ret = __os_calloc(dbenv, (size_t)nlockers,
	    sizeof(u_int32_t) * nalloc, &copymap)) != 0)
		goto err;
	memcpy(copymap, bitmap, nlockers * sizeof(u_int32_t) * nalloc);

	if ((ret = __os_calloc(dbenv, sizeof(u_int32_t), nalloc, &tmpmap)) != 0)
		goto err1;

	/* Find a deadlock. */
	if ((ret =
	    __dd_find(dbenv, bitmap, idmap, nlockers, nalloc, &deadp)) != 0)
		return (ret);

	killid = BAD_KILLID;
	free_me = deadp;
	for (; *deadp != NULL; deadp++) {
		if (abortp != NULL)
			++*abortp;
		killid = (u_int32_t)((*deadp - bitmap) / nalloc);
		limit = killid;
		keeper = BAD_KILLID;

		if (atype == DB_LOCK_DEFAULT || atype == DB_LOCK_RANDOM)
			goto dokill;
		/*
		 * It's conceivable that under XA, the locker could
		 * have gone away.
		 */
		if (killid == BAD_KILLID)
			break;

		/*
		 * Start with the id that we know is deadlocked
		 * and then examine all other set bits and see
		 * if any are a better candidate for abortion
		 * and that they are genuinely part of the
		 * deadlock.  The definition of "best":
		 * OLDEST: smallest id
		 * YOUNGEST: largest id
		 * MAXLOCKS: maximum count
		 * MINLOCKS: minimum count
		 * MINWRITE: minimum count
		 */

		for (i = (killid + 1) % nlockers;
		    i != limit;
		    i = (i + 1) % nlockers) {
			if (!ISSET_MAP(*deadp, i))
				continue;
			switch (atype) {
			case DB_LOCK_OLDEST:
				if (__dd_isolder(idmap[killid].id,
				    idmap[i].id, lock_max, txn_max))
					continue;
				keeper = i;
				break;
			case DB_LOCK_YOUNGEST:
				if (__dd_isolder(idmap[i].id,
				    idmap[killid].id, lock_max, txn_max))
					continue;
				keeper = i;
				break;
			case DB_LOCK_MAXLOCKS:
				if (idmap[i].count < idmap[killid].count)
					continue;
				keeper = i;
				break;
			case DB_LOCK_MINLOCKS:
			case DB_LOCK_MINWRITE:
				if (idmap[i].count > idmap[killid].count)
					continue;
				keeper = i;
				break;
			default:
				killid = BAD_KILLID;
				ret = EINVAL;
				goto dokill;
			}
			if (__dd_verify(idmap, *deadp,
			    tmpmap, copymap, nlockers, nalloc, i))
				killid = i;
		}

dokill:		if (killid == BAD_KILLID)
			continue;

		/*
		 * There are cases in which our general algorithm will
		 * fail.  Returning 1 from verify indicates that the
		 * particular locker is not only involved in a deadlock,
		 * but that killing him will allow others to make forward
		 * progress.  Unfortunately, there are cases where we need
		 * to abort someone, but killing them will not necessarily
		 * ensure forward progress (imagine N readers all trying to
		 * acquire a write lock).  In such a scenario, we'll have
		 * gotten all the way through the loop, we will have found
		 * someone to keep (keeper will be valid), but killid will
		 * still be the initial deadlocker.  In this case, if the
		 * initial killid satisfies __dd_verify, kill it, else abort
		 * keeper and indicate that we need to run deadlock detection
		 * again.
		 */

		if (keeper != BAD_KILLID && killid == limit &&
		    __dd_verify(idmap, *deadp,
		    tmpmap, copymap, nlockers, nalloc, killid) == 0) {
			LOCKREGION(dbenv, lt);
			region->need_dd = 1;
			UNLOCKREGION(dbenv, lt);
			killid = keeper;
		}

		/* Kill the locker with lockid idmap[killid]. */
		if ((ret = __dd_abort(dbenv, &idmap[killid])) != 0) {
			/*
			 * It's possible that the lock was already aborted;
			 * this isn't necessarily a problem, so do not treat
			 * it as an error.
			 */
			if (ret == DB_ALREADY_ABORTED)
				ret = 0;
			else
				__db_err(dbenv,
				    "warning: unable to abort locker %lx",
				    (u_long)idmap[killid].id);
		} else if (FLD_ISSET(dbenv->verbose, DB_VERB_DEADLOCK))
			__db_err(dbenv,
			    "Aborting locker %lx", (u_long)idmap[killid].id);
	}
	__os_free(dbenv, tmpmap);
err1:	__os_free(dbenv, copymap);

err:	if (free_me != NULL)
		__os_free(dbenv, free_me);
	__os_free(dbenv, bitmap);
	__os_free(dbenv, idmap);

	return (ret);
}

/*
 * ========================================================================
 * Utilities
 */

# define DD_INVALID_ID	((u_int32_t) -1)

static int
__dd_build(dbenv, atype, bmp, nlockers, allocp, idmap)
	DB_ENV *dbenv;
	u_int32_t atype, **bmp, *nlockers, *allocp;
	locker_info **idmap;
{
	struct __db_lock *lp;
	DB_LOCKER *lip, *lockerp, *child;
	DB_LOCKOBJ *op, *lo;
	DB_LOCKREGION *region;
	DB_LOCKTAB *lt;
	locker_info *id_array;
	db_timeval_t now;
	u_int32_t *bitmap, count, dd, *entryp, id, ndx, nentries, *tmpmap;
	u_int8_t *pptr;
	int expire_only, is_first, need_timeout, ret;

	lt = dbenv->lk_handle;
	region = lt->reginfo.primary;
	LOCK_SET_TIME_INVALID(&now);
	need_timeout = 0;
	expire_only = atype == DB_LOCK_EXPIRE;

	/*
	 * While we always check for expired timeouts, if we are called
	 * with DB_LOCK_EXPIRE, then we are only checking for timeouts
	 * (i.e., not doing deadlock detection at all).  If we aren't
	 * doing real deadlock detection, then we can skip a significant,
	 * amount of the processing.  In particular we do not build
	 * the conflict array and our caller needs to expect this.
	 */
	if (expire_only) {
		count = 0;
		nentries = 0;
		goto obj_loop;
	}

	/*
	 * We'll check how many lockers there are, add a few more in for
	 * good measure and then allocate all the structures.  Then we'll
	 * verify that we have enough room when we go back in and get the
	 * mutex the second time.
	 */
retry:	count = region->stat.st_nlockers;

	if (count == 0) {
		*nlockers = 0;
		return (0);
	}

	if (FLD_ISSET(dbenv->verbose, DB_VERB_DEADLOCK))
		__db_err(dbenv, "%lu lockers", (u_long)count);

	count += 20;
	nentries = ALIGN(count, 32) / 32;

	/*
	 * Allocate enough space for a count by count bitmap matrix.
	 *
	 * XXX
	 * We can probably save the malloc's between iterations just
	 * reallocing if necessary because count grew by too much.
	 */
	if ((ret = __os_calloc(dbenv, (size_t)count,
	    sizeof(u_int32_t) * nentries, &bitmap)) != 0)
		return (ret);

	if ((ret = __os_calloc(dbenv,
	    sizeof(u_int32_t), nentries, &tmpmap)) != 0) {
		__os_free(dbenv, bitmap);
		return (ret);
	}

	if ((ret = __os_calloc(dbenv,
	    (size_t)count, sizeof(locker_info), &id_array)) != 0) {
		__os_free(dbenv, bitmap);
		__os_free(dbenv, tmpmap);
		return (ret);
	}

	/*
	 * Now go back in and actually fill in the matrix.
	 */
	if (region->stat.st_nlockers > count) {
		__os_free(dbenv, bitmap);
		__os_free(dbenv, tmpmap);
		__os_free(dbenv, id_array);
		goto retry;
	}

	/*
	 * First we go through and assign each locker a deadlock detector id.
	 */
	for (id = 0, lip = SH_TAILQ_FIRST(&region->lockers, __db_locker);
	    lip != NULL;
	    lip = SH_TAILQ_NEXT(lip, ulinks, __db_locker)) {
		if (F_ISSET(lip, DB_LOCKER_INABORT))
			continue;
		if (lip->master_locker == INVALID_ROFF) {
			lip->dd_id = id++;
			id_array[lip->dd_id].id = lip->id;
			if (atype == DB_LOCK_MINLOCKS ||
			    atype == DB_LOCK_MAXLOCKS)
				id_array[lip->dd_id].count = lip->nlocks;
			if (atype == DB_LOCK_MINWRITE)
				id_array[lip->dd_id].count = lip->nwrites;
		} else
			lip->dd_id = DD_INVALID_ID;

	}

	/*
	 * We only need consider objects that have waiters, so we use
	 * the list of objects with waiters (dd_objs) instead of traversing
	 * the entire hash table.  For each object, we traverse the waiters
	 * list and add an entry in the waitsfor matrix for each waiter/holder
	 * combination.
	 */
obj_loop:
	for (op = SH_TAILQ_FIRST(&region->dd_objs, __db_lockobj);
	    op != NULL; op = SH_TAILQ_NEXT(op, dd_links, __db_lockobj)) {
		if (expire_only)
			goto look_waiters;
		CLEAR_MAP(tmpmap, nentries);

		/*
		 * First we go through and create a bit map that
		 * represents all the holders of this object.
		 */