about summary refs log tree commit diff
path: root/db2/lock/lock_deadlock.c
blob: 93c438ca36ad77efcd387ba6d8a1ea0cc0e941a4 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997
 *	Sleepycat Software.  All rights reserved.
 */

#include "config.h"

#ifndef lint
static const char copyright[] =
"@(#) Copyright (c) 1997\n\
	Sleepycat Software Inc.  All rights reserved.\n";
static const char sccsid[] = "@(#)lock_deadlock.c	10.26 (Sleepycat) 11/25/97";
#endif

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

#include <errno.h>
#include <string.h>
#include <stdlib.h>
#endif

#include "db_int.h"
#include "shqueue.h"
#include "db_shash.h"
#include "lock.h"
#include "common_ext.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;
	u_int32_t	id;
	DB_LOCK		last_lock;
	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 *, locker_info **));
static u_int32_t
	   *__dd_find __P((u_int32_t *, locker_info *, u_int32_t));

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

int
lock_detect(lt, flags, atype)
	DB_LOCKTAB *lt;
	int flags, atype;
{
	DB_ENV *dbenv;
	locker_info *idmap;
	u_int32_t *bitmap, *deadlock, i, killid, nentries, nlockers;
	int do_pass, ret;

	/* Validate arguments. */
	if ((ret =
	    __db_fchk(lt->dbenv, "lock_detect", flags, DB_LOCK_CONFLICT)) != 0)
		return (ret);

	/* Check if a detector run is necessary. */
	dbenv = lt->dbenv;
	if (LF_ISSET(DB_LOCK_CONFLICT)) {
		/* Make a pass every time a lock waits. */
		LOCK_LOCKREGION(lt);
		do_pass = dbenv->lk_info->region->need_dd != 0;
		UNLOCK_LOCKREGION(lt);

		if (!do_pass)
			return (0);
	}

	/* Build the waits-for bitmap. */
	if ((ret = __dd_build(dbenv, &bitmap, &nlockers, &idmap)) != 0)
		return (ret);

	if (nlockers == 0)
		return (0);
#ifdef DEBUG
	if (dbenv->db_verbose != 0)
		__dd_debug(dbenv, idmap, bitmap, nlockers);
#endif
	/* Find a deadlock. */
	deadlock = __dd_find(bitmap, idmap, nlockers);
	nentries = ALIGN(nlockers, 32) / 32;
	killid = BAD_KILLID;
	if (deadlock != NULL) {
		/* Kill someone. */
		switch (atype) {
		case DB_LOCK_OLDEST:
			/*
			 * Find the first bit set in the current
			 * array and then look for a lower tid in
			 * the array.
			 */
			for (i = 0; i < nlockers; i++)
				if (ISSET_MAP(deadlock, i))
					killid = i;

			if (killid == BAD_KILLID) {
				__db_err(dbenv,
				    "warning: could not find locker to abort");
				break;
			}

			/*
			 * The oldest transaction has the lowest
			 * transaction id.
			 */
			for (i = killid + 1; i < nlockers; i++)
				if (ISSET_MAP(deadlock, i) &&
				    idmap[i].id < idmap[killid].id)
					killid = i;
			break;
		case DB_LOCK_DEFAULT:
		case DB_LOCK_RANDOM:
			/*
			 * We are trying to calculate the id of the
			 * locker whose entry is indicated by deadlock.
			 */
			killid = (deadlock - bitmap) / nentries;
			break;
		case DB_LOCK_YOUNGEST:
			/*
			 * Find the first bit set in the current
			 * array and then look for a lower tid in
			 * the array.
			 */
			for (i = 0; i < nlockers; i++)
				if (ISSET_MAP(deadlock, i))
					killid = i;

			if (killid == BAD_KILLID) {
				__db_err(dbenv,
				    "warning: could not find locker to abort");
				break;
			}
			/*
			 * The youngest transaction has the highest
			 * transaction id.
			 */
			for (i = killid + 1; i < nlockers; i++)
				if (ISSET_MAP(deadlock, i) &&
				    idmap[i].id > idmap[killid].id)
					killid = i;
			break;
		default:
			killid = BAD_KILLID;
			ret = EINVAL;
		}

		/* Kill the locker with lockid idmap[killid]. */
		if (dbenv->db_verbose != 0 && killid != BAD_KILLID)
			__db_err(dbenv, "Aborting locker %lx",
			    (u_long)idmap[killid].id);

		if (killid != BAD_KILLID &&
		    (ret = __dd_abort(dbenv, &idmap[killid])) != 0)
			__db_err(dbenv,
			    "warning: unable to abort locker %lx",
			    (u_long)idmap[killid].id);
	}
	__db_free(bitmap);
	__db_free(idmap);

	return (ret);
}

/*
 * ========================================================================
 * Utilities
 */
static int
__dd_build(dbenv, bmp, nlockers, idmap)
	DB_ENV *dbenv;
	u_int32_t **bmp, *nlockers;
	locker_info **idmap;
{
	struct __db_lock *lp;
	DB_LOCKTAB *lt;
	DB_LOCKOBJ *op, *lo, *lockerp;
	u_int8_t *pptr;
	locker_info *id_array;
	u_int32_t *bitmap, count, *entryp, i, id, nentries, *tmpmap;
	int is_first, ret;

	lt = dbenv->lk_info;

	/*
	 * 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.
	 */
	LOCK_LOCKREGION(lt);
retry:	count = lt->region->nlockers;
	lt->region->need_dd = 0;
	UNLOCK_LOCKREGION(lt);

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

	if (dbenv->db_verbose)
		__db_err(dbenv, "%lu lockers", (u_long)count);

	count += 10;
	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 ((bitmap = (u_int32_t *)__db_calloc((size_t)count,
	    sizeof(u_int32_t) * nentries)) == NULL) {
		__db_err(dbenv, "%s", strerror(ENOMEM));
		return (ENOMEM);
	}

	if ((tmpmap =
	    (u_int32_t *)__db_calloc(sizeof(u_int32_t), nentries)) == NULL) {
		__db_err(dbenv, "%s", strerror(ENOMEM));
		__db_free(bitmap);
		return (ENOMEM);
	}

	if ((id_array = (locker_info *)__db_calloc((size_t)count,
	    sizeof(locker_info))) == NULL) {
		__db_err(dbenv, "%s", strerror(ENOMEM));
		__db_free(bitmap);
		__db_free(tmpmap);
		return (ENOMEM);
	}

	/*
	 * Now go back in and actually fill in the matrix.
	 */
	LOCK_LOCKREGION(lt);
	if (lt->region->nlockers > count) {
		__db_free(bitmap);
		__db_free(tmpmap);
		__db_free(id_array);
		goto retry;
	}

	/*
	 * First we go through and assign each locker a deadlock detector id.
	 * Note that we fill in the idmap in the next loop since that's the
	 * only place where we conveniently have both the deadlock id and the
	 * actual locker.
	 */
	for (id = 0, i = 0; i < lt->region->table_size; i++)
		for (op = SH_TAILQ_FIRST(&lt->hashtab[i], __db_lockobj);
		    op != NULL; op = SH_TAILQ_NEXT(op, links, __db_lockobj))
			if (op->type == DB_LOCK_LOCKER)
				op->dd_id = id++;
	/*
	 * We go through the hash table and find each object.  For each object,
	 * we traverse the waiters list and add an entry in the waitsfor matrix
	 * for each waiter/holder combination.
	 */
	for (i = 0; i < lt->region->table_size; i++) {
		for (op = SH_TAILQ_FIRST(&lt->hashtab[i], __db_lockobj);
		    op != NULL; op = SH_TAILQ_NEXT(op, links, __db_lockobj)) {
			if (op->type != DB_LOCK_OBJTYPE)
				continue;
			CLEAR_MAP(tmpmap, nentries);

			/*
			 * First we go through and create a bit map that
			 * represents all the holders of this object.
			 */
			for (lp = SH_TAILQ_FIRST(&op->holders, __db_lock);
			    lp != NULL;
			    lp = SH_TAILQ_NEXT(lp, links, __db_lock)) {
				if (__lock_getobj(lt, lp->holder,
				    NULL, DB_LOCK_LOCKER, &lockerp) != 0) {
					__db_err(dbenv,
					    "warning unable to find object");
					continue;
				}
				id_array[lockerp->dd_id].id = lp->holder;
				id_array[lockerp->dd_id].valid = 1;

				/*
				 * If the holder has already been aborted, then
				 * we should ignore it for now.
				 */
				if (lp->status == DB_LSTAT_HELD)
					SET_MAP(tmpmap, lockerp->dd_id);
			}

			/*
			 * Next, for each waiter, we set its row in the matrix
			 * equal to the map of holders we set up above.
			 */
			for (is_first = 1,
			    lp = SH_TAILQ_FIRST(&op->waiters, __db_lock);
			    lp != NULL;
			    is_first = 0,
			    lp = SH_TAILQ_NEXT(lp, links, __db_lock)) {
				if ((ret = __lock_getobj(lt, lp->holder,
				    NULL, DB_LOCK_LOCKER, &lockerp)) != 0) {
					__db_err(dbenv,
					    "warning unable to find object");
					continue;
				}
				id_array[lockerp->dd_id].id = lp->holder;
				id_array[lockerp->dd_id].valid = 1;

				/*
				 * If the transaction is pending abortion, then
				 * ignore it on this iteration.
				 */
				if (lp->status != DB_LSTAT_WAITING)
					continue;

				entryp = bitmap + (nentries * lockerp->dd_id);
				OR_MAP(entryp, tmpmap, nentries);
				/*
				 * If this is the first waiter on the queue,
				 * then we remove the waitsfor relationship
				 * with oneself.  However, if it's anywhere
				 * else on the queue, then we have to keep
				 * it and we have an automatic deadlock.
				 */
				if (is_first)
					CLR_MAP(entryp, lockerp->dd_id);
			}
		}
	}

	/* Now for each locker; record its last lock. */
	for (id = 0; id < count; id++) {
		if (!id_array[id].valid)
			continue;
		if ((ret = __lock_getobj(lt,
		    id_array[id].id, NULL, DB_LOCK_LOCKER, &lockerp)) != 0) {
			__db_err(dbenv,
			    "No locks for locker %lu", (u_long)id_array[id].id);
			continue;
		}
		lp = SH_LIST_FIRST(&lockerp->heldby, __db_lock);
		if (lp != NULL) {
			id_array[id].last_lock = LOCK_TO_OFFSET(lt, lp);
			lo = (DB_LOCKOBJ *)((u_int8_t *)lp + lp->obj);
			pptr = SH_DBT_PTR(&lo->lockobj);
			if (lo->lockobj.size >= sizeof(db_pgno_t))
				memcpy(&id_array[id].pgno, pptr,
				    sizeof(db_pgno_t));
			else
				id_array[id].pgno = 0;
		}
	}

	/* Pass complete, reset the deadlock detector bit. */
	lt->region->need_dd = 0;
	UNLOCK_LOCKREGION(lt);

	/*
	 * Now we can release everything except the bitmap matrix that we
	 * created.
	 */
	*nlockers = id;
	*idmap = id_array;
	*bmp = bitmap;
	__db_free(tmpmap);
	return (0);
}

static u_int32_t *
__dd_find(bmp, idmap, nlockers)
	u_int32_t *bmp, nlockers;
	locker_info *idmap;
{
	u_int32_t i, j, nentries, *mymap, *tmpmap;

	/*
	 * For each locker, OR in the bits from the lockers on which that
	 * locker is waiting.
	 */
	nentries = ALIGN(nlockers, 32) / 32;
	for (mymap = bmp, i = 0; i < nlockers; i++, mymap += nentries) {
		if (!idmap[i].valid)
			continue;
		for (j = 0; j < nlockers; j++) {
			if (ISSET_MAP(mymap, j)) {
				/* Find the map for this bit. */
				tmpmap = bmp + (nentries * j);
				OR_MAP(mymap, tmpmap, nentries);
				if (ISSET_MAP(mymap, i))
					return (mymap);
			}
		}
	}
	return (NULL);
}

static int
__dd_abort(dbenv, info)
	DB_ENV *dbenv;
	locker_info *info;
{
	struct __db_lock *lockp;
	DB_LOCKTAB *lt;
	DB_LOCKOBJ *lockerp, *sh_obj;
	int ret;

	lt = dbenv->lk_info;
	LOCK_LOCKREGION(lt);

	/* Find the locker's last lock. */
	if ((ret =
	    __lock_getobj(lt, info->id, NULL, DB_LOCK_LOCKER, &lockerp)) != 0)
		goto out;

	lockp = SH_LIST_FIRST(&lockerp->heldby, __db_lock);
	if (LOCK_TO_OFFSET(lt, lockp) != info->last_lock ||
	    lockp == NULL || lockp->status != DB_LSTAT_WAITING)
		goto out;

	/* Abort lock, take it off list, and wake up this lock. */
	lockp->status = DB_LSTAT_ABORTED;
	lt->region->ndeadlocks++;
	SH_LIST_REMOVE(lockp, locker_links, __db_lock);
	sh_obj = (DB_LOCKOBJ *)((u_int8_t *)lockp + lockp->obj);
	SH_TAILQ_REMOVE(&sh_obj->waiters, lockp, links, __db_lock);
        (void)__db_mutex_unlock(&lockp->mutex, lt->fd);

	ret = 0;

out:	UNLOCK_LOCKREGION(lt);
	return (ret);
}

#ifdef DEBUG
static void
__dd_debug(dbenv, idmap, bitmap, nlockers)
	DB_ENV *dbenv;
	locker_info *idmap;
	u_int32_t *bitmap, nlockers;
{
	u_int32_t i, j, *mymap, nentries;
	char *msgbuf;

	__db_err(dbenv, "Waitsfor array");
	__db_err(dbenv, "waiter\twaiting on");
	/*
	 * Allocate space to print 10 bytes per item waited on.
	 */
	if ((msgbuf = (char *)__db_malloc((nlockers + 1) * 10 + 64)) == NULL) {
		__db_err(dbenv, "%s", strerror(ENOMEM));
		return;
	}

	nentries = ALIGN(nlockers, 32) / 32;
	for (mymap = bitmap, i = 0; i < nlockers; i++, mymap += nentries) {
		if (!idmap[i].valid)
			continue;
		sprintf(msgbuf,					/* Waiter. */
		    "%lx/%lu:\t", (u_long)idmap[i].id, (u_long)idmap[i].pgno);
		for (j = 0; j < nlockers; j++)
			if (ISSET_MAP(mymap, j))
				sprintf(msgbuf, "%s %lx", msgbuf,
				    (u_long)idmap[j].id);
		(void)sprintf(msgbuf,
		    "%s %lu", msgbuf, (u_long)idmap[i].last_lock);
		__db_err(dbenv, msgbuf);
	}

	__db_free(msgbuf);
}
#endif