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lock_deadlock.c

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *    Sleepycat Software.  All rights reserved.
 */

#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)lock_deadlock.c     10.37 (Sleepycat) 10/4/98";
#endif /* not lint */

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

#include <errno.h>
#include <string.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 DIAGNOSTIC
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;
      u_int32_t flags, atype;
{
      DB_ENV *dbenv;
      locker_info *idmap;
      u_int32_t *bitmap, *deadlock, i, killid, nentries, nlockers;
      int do_pass, ret;

      LOCK_PANIC_CHECK(lt);

      /* 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 DIAGNOSTIC
      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);
      }
      __os_free(bitmap, 0);
      __os_free(idmap, 0);

      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 ((ret = __os_calloc((size_t)count,
          sizeof(u_int32_t) * nentries, &bitmap)) != 0)
            return (ret);

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

      if ((ret =
          __os_calloc((size_t)count, sizeof(locker_info), &id_array)) != 0) {
            __os_free(bitmap, count * sizeof(u_int32_t) * nentries);
            __os_free(tmpmap, sizeof(u_int32_t) * nentries);
            return (ret);
      }

      /*
       * Now go back in and actually fill in the matrix.
       */
      LOCK_LOCKREGION(lt);
      if (lt->region->nlockers > count) {
            __os_free(bitmap, count * sizeof(u_int32_t) * nentries);
            __os_free(tmpmap, sizeof(u_int32_t) * nentries);
            __os_free(id_array, count * sizeof(locker_info));
            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 (__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 (__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;
      __os_free(tmpmap, sizeof(u_int32_t) * nentries);
      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);

      /*
       * It's possible that this locker was already aborted.
       * If that's the case, make sure that we remove its
       * locker from the hash table.
       */
      if (lockp == NULL) {
            HASHREMOVE_EL(lt->hashtab, __db_lockobj,
                links, lockerp, lt->region->table_size, __lock_lhash);
            SH_TAILQ_INSERT_HEAD(&lt->region->free_objs,
                lockerp, links, __db_lockobj);
            lt->region->nlockers--;
            goto out;
      } else if (LOCK_TO_OFFSET(lt, lockp) != info->last_lock ||
          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->reginfo.fd);

      ret = 0;

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

#ifdef DIAGNOSTIC
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;
      int ret;
      char *msgbuf;

      __db_err(dbenv, "Waitsfor array");
      __db_err(dbenv, "waiter\twaiting on");

      /* Allocate space to print 10 bytes per item waited on. */
#undef      MSGBUF_LEN
#define     MSGBUF_LEN ((nlockers + 1) * 10 + 64)
      if ((ret = __os_malloc(MSGBUF_LEN, NULL, &msgbuf)) != 0)
            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);
      }

      __os_free(msgbuf, MSGBUF_LEN);
}
#endif

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