db/lock/lock_deadlock.c

	lock_deadlock.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*-
 * 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